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TRANSCAT Pipette Calibration Project 05417

1 INTRODUCTION:..........................................................................................2

2 RECOGNIZE AND QUANTIFY NEED...........................................................2

2.1 Project Mission Statement:..............................................................................2

2.2 Company Background.......................................................................................2

2.3 Calibration: An element of Metrology...........................................................2

2.4 Product Description...........................................................................................2

2.5 Scope Limitations...............................................................................................2

2.6 Stakeholders:.......................................................................................................2

2.7 Key Business Goals:..........................................................................................2

2.8 Top Level Critical Financial Parameters.......................................................2

2.9 Financial Analysis..............................................................................................2

2.10 Primary Market....................................................................................................2

2.11 Secondary Market...............................................................................................2

2.12 Order Qualifiers...................................................................................................2

2.13 Order Winners......................................................................................................2

2.14 Formal Statement of Work................................................................................2

3 CONCEPT DEVELOPMENT.........................................................................2

3.1 Concept Development Process......................................................................2

3.2 Brainstorming Session......................................................................................2

3.3 Conceptual Level Drawing...............................................................................2

3.4 Mechanical Concepts........................................................................................23.4.1 Plunger Depression..........................................................................................2

3.4.1.1 Stepper Motor..............................................................................................23.4.1.2 Pneumatic Systems......................................................................................2

3.4.2 Stand................................................................................................................23.4.2.1 Stand with vertical movement.....................................................................2

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3.4.2.2 Stand with radial movement........................................................................23.4.2.3 The Basic Stand...........................................................................................2

3.4.3 Vial Holder......................................................................................................23.4.3.1 The Simple Block........................................................................................23.4.3.2 The CMM Set up.........................................................................................2

3.5 Electrical Concept..............................................................................................23.5.1 Micro-controller...............................................................................................2

3.5.1.1 8051 Micro-controller..................................................................................23.5.1.2 DIOS Micro-controller................................................................................23.5.1.3 PIC Micro-controller...................................................................................23.5.1.4 BASIC Stamp Micro-controller...................................................................2

3.5.2 Vertical Movement Sensors.............................................................................23.5.2.1 Hall Effect Sensor........................................................................................23.5.2.2 Reed Switch.................................................................................................23.5.2.3 Magneto Resistive Devices..........................................................................2

3.5.3 Radial Movement Sensors...............................................................................23.5.3.1 Infra Red Proximity Detector (IRPD)..........................................................23.5.3.2 Potentiometer...............................................................................................23.5.3.3 Optical Interrupter.......................................................................................2

4 FEASIBILITY ASSESSMENT........................................................................2

4.1 The Stand..............................................................................................................24.1.1 Stand Concepts:...............................................................................................24.1.2 Attributes:........................................................................................................24.1.3 Level of Attainment Analysis..........................................................................24.1.4 Critical/Important Attribute List......................................................................24.1.5 Second Level of Attainment Analysis.............................................................24.1.6 Performance Feasibility...................................................................................24.1.7 Economic Feasibility.......................................................................................24.1.8 Technical Feasibility........................................................................................24.1.9 Schedule Feasibility.........................................................................................24.1.10 Final Decision..................................................................................................2

4.2 Plunger Depression............................................................................................24.2.1 Plunger Depression Attributes:........................................................................24.2.2 Concepts:.........................................................................................................24.2.3 Level of Attainment Analysis..........................................................................24.2.4 Performance Feasibility...................................................................................24.2.5 Economic Feasibility.......................................................................................24.2.6 Technical Feasibility........................................................................................24.2.7 Schedule Feasibility.........................................................................................24.2.8 Final Decision..................................................................................................2

4.3 The Micro-controller...........................................................................................2

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4.3.1 Micro-controller Concepts:..............................................................................24.3.2 Attributes:........................................................................................................24.3.3 Level of Attainment Analysis..........................................................................24.3.4 Performance Feasibility...................................................................................24.3.5 Economic Feasibility.......................................................................................24.3.6 Technical Feasibility........................................................................................24.3.7 Schedule Feasibility.........................................................................................24.3.8 Final Decision..................................................................................................2

4.4 Sensors for Vertical Tracking..........................................................................24.4.1 Concepts for Vertical Tracking:......................................................................24.4.2 Vertical Tracking Attributes:...........................................................................24.4.3 Level of Attainment Analysis..........................................................................24.4.4 Performance Feasibility...................................................................................24.4.5 Economic Feasibility.......................................................................................24.4.6 Technical and Schedule Feasibility.................................................................24.4.7 Final Decision..................................................................................................2

4.5 Radial Movement Sensors................................................................................24.5.1 Concepts for radial tracking:...........................................................................24.5.2 Attributes:........................................................................................................24.5.3 Level of Attainment Analysis..........................................................................24.5.4 Performance Feasibility...................................................................................2

5 SPECIFICATIONS, ANALYSIS AND SYNTHESIS.....................................26

5.1 Mechanical Analysis & Synthesis..................................................................25.1.1 Problem Statement...........................................................................................25.1.2 Known Information.........................................................................................25.1.3 Desired Information.........................................................................................25.1.4 Assumptions....................................................................................................25.1.5 Data and Analysis............................................................................................25.1.6 Quality Review................................................................................................2

5.2 Electrical Analysis..............................................................................................25.2.1 Design Specifications:.....................................................................................25.2.2 Micro-controller Specifications:......................................................................25.2.3 Sensor Specifications:......................................................................................25.2.4 Power Supply Specifications:..........................................................................25.2.5 Micro-controller...............................................................................................2

5.2.5.1 Selection of Micro-controller......................................................................25.2.5.2 Integration with Electrical System...............................................................25.2.5.3 Inputs:..........................................................................................................25.2.5.4 Outputs:........................................................................................................25.2.5.5 Serial:...........................................................................................................2

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6 BILL OF MATERIALS...................................................................................2

APPENDIX A: SYSTEM SCHEMATIC.................................................................2

APPENDIX B: ELECTRICAL SYSTEM................................................................2

APPENDIX C: FLOW CHART OF SYSTEM........................................................2

APPENDIX D: BEER-LAMBERT’S LAW...........................................................61

Appendix E: Hall Effect........................................................................................61

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1 Introduction:

Pipettes are widely used for delivering liquids in chemistry and life

sciences laboratories, where their accuracy and precision are critical to achieving

good results. In recent years, much attention has been focused on how best to

calibrate these devices in centralized metrology laboratories, but little attention

has been given to assuring good quality of liquid delivery in the place of use.

Transcat has noted this and is currently looking into ways to calibrate these

devices so as to expand the range of services.

Current calibration procedures require a technician with many hours of

training to manually operate a pipette and measure how much fluid is transported

compared to how much is metered on the pipette. Tools that are used for this

form of calibration are the Artel PCS ® colorimetric calibrator and the Artel

Pipette Tracker® software. These tools take the guesswork out of measuring the

fluid delivered and also perform the statistical equations needed to find the

accuracy and precision of the micropipette. To be specific the technician inserts

the fluid from the pipette into a vial that is inside of the PCS®, which then uses

Beer-Lambert’s Law to find the volume that is inside the vial. We will explain this

law later in the paper. The PCS® then uses serial communication to send the

results to the Pipette Tracker® software which then perform statistical equations.

Unfortunately the human interface tends to create quite a bit of variability

in the calibration process. That is why Transcat desired to create a system which

will automate the system as much as possible so as to reduce the variability and

increase the reliability of calibration process. Our current design will accomplish

this primarily by use of pneumatics.

The semi automatic pipette calibrator will require the technician to start by

inputting the unique code for the pipette in computer interface. The technician will

then be prompted to move the device over the vial containing the fluid, which is

the starting position. The device will then submerge the pipette tip into the fluid

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and, once told to by the technician; will aspirate the liquid into the pipette tip. The

pipette will then be raised and the technician will be prompted to move the device

over the calibrator. Again, the device will insert the pipette tip into a vial. Then the

technician will prompt the device to first dispense the fluid and then clear out the

tip. The pipette will be raised again and the process will be repeated. This cycle

will go on for 15 times, with three runs each at five equidistant volumes within the

range of the pipette.

2 Recognize and Quantify Need2.1 Project Mission Statement:

The goal of student engineering design team was to investigate viable

processes and approaches to semi automate the pipette calibration process for

as many pipette as possible. The final design consist of several pneumatic

cylinders, a manually turning stand, several sensors to find the precise

positioning of pipette, a computer interface for the technician, as well as the Artel

PCS® and the Pipette Tracker® software.

2.2 Company BackgroundTranscat is one of North America's leading providers of calibration services and

instrumentations. Since its' incorporation in 1964, Transmation (now Transcat)

concentrated on developing, servicing and distributing electronic instrumentation

used in the monitoring, calibration, and supervision. The primary markets for

Transcat's services are process, life sciences, manufacturing, communications,

automotive, and aerospace industries.

Transcat, Inc.'s former manufacturing organization located in Rochester, New

York, was comprised of the Transmation Instrument Division, established in

1964, and Altek Industries, which was purchased by Transmation, Inc. in 1996.

The two groups combined in 1999 to form the Products Group in 1980, the

Transcat (short for "Transmation Catalog") Division was established as a catalog

sales operation to offer customers a single source for calibration and test

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instrumentation. This operation has grown into a full-fledged industrial distribution

network for not only Transmation and Altek products, but also those of more than

200 other manufacturers.

As catalog sales increased at a dramatic pace, it became evident that this type of

equipment would require periodic recalibration and general maintenance in order

to perform at peak level. Thus, in 1988, Transcat opened the first of many

calibration laboratories to service customer equipment. The purchase of E.I.L. in

1997 and MeterMaster in 1999 (both distributors & calibration service

organizations with laboratories located throughout the United States and

Canada) established Transcat as the leading calibration service provider in the

U.S. Finally, the newest business unit of Transcat established in 1999,

MetersandInstruments.com, provides customers with an "Internet" channel for

the purchase of calibration equipment and tools. In late 2001, as part of their

strategy to divest non-core businesses, Transcat sold both the Products Group

Division and the MAC (Measurement and Control) Division. This allowed them to

focus on providing innovative, quality products and calibration services to their

customers. Upon completion of the sale, the company name was changed from

Transmation, Inc. to Transcat, Inc. Today, Transcat, Inc. employs 230 talented

individuals throughout the U.S., Canada, and China.

2.3 Calibration: An element of Metrology

Metrology is a branch of science that was created in France and consists

of the quantification of weights and measurement. Metrology is used in everyday

life to make sure that the instruments and the systems that we use can

accurately and reliably perform its designated task. Due to many cases of fraud

in market place there were laws that were created to regulate these

measurements. Today scientists instead of lawyers handle the regulation of

measurement, and they are formed at an international basis so as to create a

common base for all researchers to work on. With this cooperation, the level of

precision of measurements has risen considerably, improving not only the

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methods of research but also improving the quality of the products created by

this research.

Of particular interest to quality control (QC) is the element of metrology

called calibration. Calibration is the process of comparing measurements, made

by an instrument with a standard. The instrument, which is of unconfirmed

accuracy, is referred as the unit under test (UUT) and the instrument of known

accuracy is known as a measurement standard. Calibration is performed to

establish the accuracy of the UUT for measurements. Instruments that do not

meet the standards are adjusted and then tested again until they meet the

standards.

2.4 Product Description

The primary goal of students on the Transcat design team was to design, build,

test, and debug a working prototype device that incorporates a majority of the

design and will work under the specifications listed below:

Test Stand: A mechanical setup that will hold the pipette in place as the

calibration is performed. The test stand will move in two directions,

vertically and either rotationally or horizontally.

Plunger Depression Device: A mechanical device that will insure the

proper amount of force will be applied for the depression of the plunger for

both the dispensing and tip blow out phases of pipette evacuation.

Automated Digital Controls for some of the above features and for the

data interface to the PCS® and Pipette Tracker® software.

User Interface for the technician. This interface will allow the technician to

properly use the semi-automated system. This could be either a physical

or graphical interface.

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2.5 Scope Limitations

The prototype was fully designed by the end of the fall quarter and a

working device will be completed by the end of the spring quarter. At the end of

the fall quarter the senior design team presented the preliminary design, detail

sketches, and cost for the components needed to build the prototype. During the

spring quarter, the design team will participate in on-site testing, data collection,

and evaluation of prototype device.

As with any design, though, there are limitations to the scope. This simply

means the design will only be able to perform a specific set of tasks. The tasks

that we are designing for will meet the customer requirements as discussed

between the team and the customer.

The design team will be responsible for a device that:

Automates the human element of the calibration process

o Depressing the plunger

o Raising and lowering the pipette

Maintains a .25% accuracy in liquid dispensed during the calibration

process

Performs three measurements at each of five equidistant points within the

volumetric range of the pipette.

Keeps the pipette vertical within +/- 1 degree

Prevent light from contaminating the photosensitive fluids

Reduce human vibrations by use of semi-automation.

Allows human control over the processes being performed by use of the

Graphical User Interface.

Has a complete user’s manual for future reference.

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The design team will not be responsible for:

Taking apart the micropipettes to perform manual replacement of parts

Calibrating the Artel PCS® colorimetric pipette calibrator.

Initiating changes to the Artel Pipette Tracker® software.

Training individual users on the setup after the product has been

integrated into the everyday process of calibration.

2.6 Stakeholders:

The primary stakeholder for the research and development of the semi

automated system is Transcat, since the device will be integrated with the PCS®

and Pipette Tracker® software. The students are the secondary stakeholders in

this project because it will satisfy the engineering curriculum requirements for the

students in the design team and it will serve as a learning experience for them.

Eventually, the entire calibration industry could be a stakeholder, especially

seeing as not much work has been done in the field of automating colorimetric

calibration.

2.7 Key Business Goals:

In the field of calibration slight differences in precision can make the

difference between success and failure. After all, everyday more and more

companies are providing calibration services making the competition very tight.

Because of this is necessary for the variation to be as small as possible. Seeing

as the laboratories are at controlled environments, one can rule out variation due

to surrounding and concentrate instead on the variations caused by the

technicians. The main way to get rid of this is, of course, by removing as much

interaction as possible by use of automation. This prototype aspires to do as

much of this as possible, giving Transcat the competitive edge needed to

succeed in this field of calibration.

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2.8 Top Level Critical Financial Parameters

The top level critical financial parameters related to the project are

associated with the following components that are needed to build the prototype.

The pneumatic cylinders

The controls for the pneumatic cylinders

The micro-controller for the system

2.9 Financial Analysis

The team has been given a definite budget of $500 by Transcat.

Therefore, it is important that the team create a low cost system to fit this budget.

The most costly component will likely be the pneumatic cylinders that will actuate

the system. The total cost of the system will depend on the following

components:

The cylinder

Microprocessor

The sensors

The pneumatic controls

Bearings for rotation

The pipette holding fixture

Raw materials needed to create the base

Magnets to be put on the cylinder piston head

Miscellaneous electrical and mechanical components

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2.10 Primary Market

The primary market will be Transcat because the system is customized to

be used in their lab.

2.11 Secondary Market

The secondary market will be any other company that is interested in providing

colorimetric calibration services for micropipettes. In order for this system to be

part of the secondary market, modification will have to be made to the design to

enable it to be mass-produced.

2.12 Order Qualifiers

The primary market requires is that this prototype performs calibration runs with a

variation at or under 0.25% of volume dispensed. The setup will have to be able

to fit in the laboratory.

2.13 Order Winners Universal acceptance of pipettes

Reduce test time

Simpler calibration procedure

Simpler setup

Meeting all the project requirements

2.14 Formal Statement of Work

The RIT engineering designing team shall work closely with Transcat

technical staff to understand customer’s needs and incorporate these

requirements into the final product. The team will research through the

appropriate means to identify the various methods to which they will be able to

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automate the colorimetric calibration process. The design team will take part

constructive and on going discussion to understand the need for the balance

between the desires of the engineers, the needs of the customer, and product

feasibility. The team will also create appropriate design and specification options

that will be reviewed by Transcat. The design team is primarily concerned with

building a working prototype that incorporates all the project requirements that

were agreed upon with Transcat. In addition, the team will perform testing, data

collection, and evaluation of the prototype period. The design team will prepare a

professional written report including complete technical specification,

construction information, and experimental results, along with other information

that will be presented to the corporate managers.

Transcat will provide the engineering design team with a technical point of

contact that will provide guidance, along with feedback and field engineering

information pertaining to the operation requirements and use of the system. In

addition, they will provide access to relevant support information, including

documentation and case studies, which will be needed to complete the project,

along with access to their local calibration laboratory for insight operation and

testing evaluation. Financial support for all components needed in the build will

also be provided. All measurement instruments and components associated with

project are subject to Transcat review and approval.

Agreed by:

Jeff Youngs ____________________ Date:_______(Design Team Leader)

Jon Schneider___________________Date:_______(ME Design Team Member)

Ashish Rathour__________________Date:_______( EE Design Team Member)

Glenn Carroll____________________Date:_______(EE Design Team Member)

Tai To_________________________Date:________(EE Design Team Member)

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Mayank Rathour_________________Date:________(EE Design Team Member)

Howard Zion____________________Date:________(Customer Representative)

Rainer Stellrecht_________________Date:________(Customer Representative)

George Slack___________________Date:________(Faculty Coordinator)

Mark Hopkins___________________Date:________(Faculty Mentor)

Wayne Walter___________________Date:________(Faculty Mentor)

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3 Concept Development3.1 Concept Development Process

The concept development process has the main objective of developing

several design objectives that will each meet the design specifications and to

improve these ideas through interaction among team members. The design team

use brainstorming technique to produce variety of concepts that would be used in

further discussion. Team members also sketch conceptual drawings to provide a

clear picture of some of the proposed concepts. Finally, the team use the design

specifications to develop the ideas into a useful form.

3.2 Brainstorming Session

In the brainstorming session each of the team members pitched in to

create a large quantity of concept that could be used in creation of prototype. The

design team listed concepts on different design components of the project. A list

of these concepts was made and each of the team members was given two

votes for each component so that they could identify which concept that they

thought best met the design of specifications. The voting also helped in

consolidation of concepts. Table 1 shows the ideas generated during the

mechanical portion of the brainstorming session and how popular each concept

was.

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Design Component Concept Votes Rank

Plunger depression 1 Stepper motor 7 1

2 Pneumatic system 5 2

3 Hydraulic system 0 3

4 Spring Loading 0 3

5 Ratcheting mechanism 0 3

Stand 1 No stand 1 3

2 Basic stand 3 2

3

Stand with vertical

movement 4 1

4

Stand with radial

movement 4 1

5 Clamps 0 4

Vial Holder 1 Block 12 1

2 CMM setup (Grid) 0 2

Table 1 Mechanical Brainstorming Session

Afterwards the team voted on the electrical concepts of the prototype. The concept and

their popularity are listed in Table 2.

Design Component Concept Votes Rank

Microprocessor 1 8051 2 2

2 Pic Micro 7 1

3 Basic Stamp 1 3

4 DIOS 2 2

Vertical Movement

Sensors 1 Hall Effect Sensor 11 1

2 Reed Switch 0 3

3 Magneto Resistive Device 1 2

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Radial Movement

Sensors 1 Infra Red ( IRPD) 1 2

2 Sonar 0 3

3 Potentiometer 1 2

4 Optical Interrupter 10 1

5 Hair Trigger Switch 0 3

Table 2 Electrical Brainstorming Session

3.3 Conceptual Level Drawing

The team members that have the most popular designs then created

conceptual level drawings of these designs. These drawings were used to help

the team obtain an idea of how the concept would work. These conceptual

drawings can be found in appendix A.

3.4 Mechanical Concepts

Each of the design components has the list of concepts related to them.

The design team discussed top two or three concepts for each design

component.

3.4.1 Plunger Depression

In order to transport the fluids, the operator needs to depress the plunger

and release it in the fluid to draw it into the pipette tip, and then dispense the fluid

and blow out the tip. As one can imagine this was one of the most important

parts of the project. Therefore, much emphasis was put into in depth

explanations of the top two concepts.

3.4.1.1 Stepper Motor

This concept had two possible implementations. Each of them used the

precise movement of the stepper motor to its advantage. The first idea was to

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attach a gear to the shaft of the stepper motor and use the gear to drive a pinion

gear. This pinion would actuate vertically in order to either depress or release the

plunger of the pipette. The simplicity of this design was rather attractive to the

team. The other idea was to attach a lead screw to the shaft of the stepper

motor. A nut would be attached to the lead screw. In order to prevent the nut

from merely turning along with the screw, the nut had to be properly restrained.

There were several ideas as how to do this, but the winning idea had the nut

constrained by two arms that would run on two tracks that are part of the setup.

Several team members noted that this setup would be rather difficult to repair

should any problems arise. This was noted and brought up later in the feasibility

assessment.

3.4.1.2 Pneumatic Systems

This concept was originally unpopular due to the misconception that the system

would be very expensive. This was due to the fact that most of the pneumatic

systems that the team had viewed included an expensive system of machine

made servos. After this misunderstanding was cleared, the team was more eager

to work with this concept. At the time, the team felt that a simple pneumatic

cylinder with a spring return system would suffice. As per the control of the

pneumatic cylinder, the team felt that there were only two points of interest; that

of the first phase of depression and the blowout phase. Each of these phases

had their own unique range of pressures allowed and these pressures could

easily be converted to forces by taking into account the surface area of the piston

head. Therefore, one could control the system by using two distinct pressures,

each near the separation point between the two phases. All one would need to

go from one phase to the other would be a simple switching mechanism for the

two distinct pressures.

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3.4.2 Stand

Seeing as this part of the design would be holding the actual pipette in

place, this is easily one of the most important parts of the design. At the time the

team was divided on whether or not to actually have this stand move. The top

three concepts are listed below:

3.4.2.1 Stand with vertical movement

This concept was one of the hardest to conceptualize. The reason for this

was the fact that it would have to act against the forces of gravity and moving in

accurate manner. One of the first ideas that came up was to use a stepper motor

with a gear attach to its shaft and to have this gear interact with a pinion gear.

This time, however, the stepper would be the moving part instead of the pinion.

After consideration, we found that this would not be usable due to two reasons:

the resolution of movement would be too inaccurate and even if the gear teeth

were small enough to accommodate for accuracy, the teeth would then not be

able to support the relatively heavy load. It was at this time that we considered

the use of a pneumatic cylinder for the linear actuation. The piston would be

double acting, in which there would be two air supplies, one in the inlet orifice

and the other in the exhaust orifice. These two supplies would act against each

other so as to let the piston inside the cylinder move in a gradual manner instead

of slamming it into its fully opened and fully closed positions.

3.4.2.2 Stand with radial movement

Though the title of this concept refers only to radial movement, there was

talk of horizontal movement along with radial movement as we discussed this

concept.

When it comes to horizontal movement, we had quite a few ideas. One of

the first ideas was to use a manually operated trolley system. In this idea, a

simple “trolley”, which was actually a piece of metal with four wheels attached to

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it, would have its wheels inside of an extruded piece of plastic. One could then

move the trolley back and forth with a fairly smooth movement. One of the main

problems, however, was the fact that there would be no speed control, thereby

allowing for the possibility of the trolley coming to an extremely abrupt stop. We

found, after a few rounds of experimentation, that abrupt stops such as these

tend to cause extreme errors in calibration, mainly due to the fluid becoming

stuck in the tip. After we done with this idea, we advanced to the possibility of

moving the calibration fluid and calibrator instead of moving the pipette. To be

specific, we thought it would be a good idea to attach a table to the top of a

pneumatic cylinder. This cylinder would also be double acting so as to reduce the

possibility of jerky movements in the process. However, as will be seen in the

feasibility assessment, this option was rather expensive, especially for a small

budget such as ours.

When it came to radial movement we had a fair share of ideas as well.

One of the first ideas was to automate this by use of a rotating turntable. In

theory, this idea would work rather well. We would merely need to use a DC

Motor to turn the whole set up and use a system of bearings to make the

movements as smooth as possible. However, as with the other table idea, we

found that this was a rather expensive method and that it would be fairly hard to

control. The team’s other idea was that of manually moving the stand by use of a

simple handle. Again, we would have to use a system of bearings in order to

make the movements smooth, but with this setup, it would be rather easy to

create a system of stops to properly restrain the movement. The simplicity of the

set up made particularly attractive.

3.4.2.3 The Basic Stand

This setup merely called for the use of a rod that was fixed to the ground.

We thought of this concept when we were putting together an experimental setup

for preliminary data collection. In the experimental setup, we had a ring stand

that we attached specially made clamps to. Seeing as the results that were

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obtained from this experimental setup weren’t very inaccurate, this made the

possibility of using such a simple set up in our final design seem very plausible.

However, we also had to think about how inconvenient such a set up would be

for the technician that would have to use it.

3.4.3 Vial Holder

Though it may seem a very simple component to the system, the restraint

of the vial plays a very critical role in the calibration process. After all, one needs

to have a common place for the vial to be located at if one wants to efficiently use

their time when calibrating. Also, a restraint would help to prevent the vial from

spilling in case an accident should happen.

3.4.3.1 The Simple Block

As the title suggests, this setup is quite simple. One merely has to get a

block of certain material, possibly wood, and drill a hole into it, so that the vial will

fit into the block. This will be enough to satisfy the two criteria that the team set

for this design component.

3.4.3.2 The CMM Set up

This set up is based on the system used by Coordinate Measurement

Machinery (CMM). In this set up, there is a grid on the table and each of the

coordinates has a screw hole in it. The purpose of these holes is to allow various

attachments to be placed on the table in a secure fashion. This is very useful for

securing parts that are unusual shapes, but we are merely working with a

commonly shaped vial. Thus, the design would be too advanced for our needs.

Still, the grid is rather useful for a coordinate system for the movement of the

pipette. However, the two positions that the pipette would be moving to will be

fixed, negating the need for a coordinate system.

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3.5 Electrical Concept3.5.1 Micro-controller

In order to maintain control of the system, we found it necessary to include a

micro-controller. This component would keep track of all the actions and,

depending on state of the system, would tell the system to perform certain

actions. This is the heart of the electrical system.

3.5.1.1 8051 Micro-controller

The 8051 is an 8-bit microprocessor originally designed in the 1980's by

Intel that has gained great popularity since its introduction. Its standard form

includes several standard on-chip peripherals, including timers, counters, and

UART's, plus 4k bytes of on-chip program memory and 128 bytes (note: bytes,

not Kbytes) of data memory, making single-chip implementations possible. Its

hundreds of derivatives, manufactured by several different companies (like

Philips) include even more on-chip peripherals, such as analog-digital converters,

pulse-width modulators, I2C bus interfaces, etc. Costing only a few dollars per

IC, the 8051 is estimated to be used in a large percentage of all embedded

system products.

3.5.1.2 DIOS Micro-controller

The DIOS Micro-controller made by Kronos Robotics is an 8 bit micro

controller that comes in both 28 and 40 pin packages. The 40-pin package has

33 I/O pins, 8 A/D ports, and a 40 MHz internal clock. It includes 32 Kbytes of

program space (16 Kbytes for user programs), 256 bytes of internal memory, and

a programming port that, along with the RS232 interface included on the carrier

board can be used to communicate with the PC. The DIOS uses a form of the

BASIC language and can interface with a simple Visual Basic GUI on a PC. The

compiler software is available for free from Kronos Robotics.

3.5.1.3 PIC Micro-controller

22


The PIC Micro-controller is yet another 8-bit micro-controller. PICs are

available in a wide range of packages and amount of pins. They are also

available in a wide range of internal clock speeds and a considerably large range

of memory size. There is a wide range of compilers available for them, however

the better ones are not free. An evaluation board is not necessary for its

operation, however a programming board or socket is required to program the

PIC. These range in price from the affordable $50, designed for on PIC in

particular, to the extreme $1000 programmers that can program any PIC you

throw at it

3.5.1.4 BASIC Stamp Micro-controllerBASIC Stamp is a micro-controller made by Parallax. They are available in

24 and 40 pin packages. Like the DIOS, they run on a form of the BASIC

language, making them easy to program. They have a serial port for

programming and interfacing with a PC.

3.5.2 Vertical Movement Sensors

This form of sensor would keep track of the vertical movement of the

stand. After much research, we found that some of the easiest and most widely

accepted sensors had to do with magnetism. This formed our concept

development, as one can see from table 2.

3.5.2.1 Hall Effect Sensor

This proximity sensor is very cheap and very compact. These sensors are

basically mounted to the side of the stand and keep track of any magnetic fields

around them. The theory behind the Hall effect is talked about in more detail in

Appendix E. These sensors are especially useful in pneumatic setups, because

most suppliers readily supply air cylinder with magnets on piston heads. This

way, one can see where the piston head is by keeping track of the magnetic field

around it.

23


3.5.2.2 Reed Switch

This sensor is not a sensor at all. It is, as the name implies, merely a

switch. Its resolution is rather poor, with it closing the circuit it is on when a

magnetic field is up to 0.2 inches away and opening the circuit when the

magnetic field is at least 0.3 inches away. While these measurements may seem

small, they could easily ruin our system if they presented themselves.

3.5.2.3 Magneto Resistive Devices

These devices are quite similar to Hall Effect sensors. The main difference

between these two sensors is that the MRD sensors measure the change in a

magnetic field instead of the presence of one. This is accomplished by a variable

resistor in the device that changes value as the strength of the magnetic field

changes. This would be very useful if we were to keep track of how far away a

piston head is, if that piston head has a magnet on it.

3.5.3 Radial Movement Sensors

At this point of our project, we had decided to use radial movement

instead of horizontal movement. The fact that the path of motion is curved

instead of straight may for a fairly difficult concept development. However, this

difficulty inspired us to think of some fairly inventive sensor setups, as one can

see below.

3.5.3.1 Infra Red Proximity Detector (IRPD)

The IRPD is a proximity sensor, that is to say that it merely detects if

object is there or not. The IRPD acts both as a transmitter and receiver of an

infra red light beam. The beam reflects back to the sensor and is only noticed by

the receiver if the distance of reflection is small enough so that the infra red light

does not diffract too much. This is a fairly cheap and easy to mount sensor, but it

is very limited to its uses in a real world scenario.

24


3.5.3.2 Potentiometer

The potentiometer is a variable resistor that gains resistance as the knob

is turned further away from its starting point. This is achieved by setting one end

of a circuit at the starting point and the other end of the circuit on a piece of metal

that is attached to the knob of the potentiometer. The piece of metal travels on a

resistive film, and as it goes further away from the starting point, there is more

and more resistive film in the circuit, increasing the resistance. One can keep

track of just how far the knob has rotated by either keeping track of voltage in the

circuit or finding the RC Time constant for a circuit containing the potentiometer

and a common capacitor. Either way, one has to experimentally find some

constant values for certain known angles of rotation. One can then linearly

interpolate values based on these known constants. We can use this to our

advantage by attaching a potentiometer to the stand and seeing how much the

knob turns as the shaft it is attached to moves.

3.5.3.3 Optical Interrupter

This sensor is very similar to the IRPD in concept. The difference, though,

is that the transmitter and receiver of the infrared light are two different parts. The

Optical Interrupter keeps track of any objects in its limited vicinity by seeing if any

infra red light reaches the receiver. If not, something is in the path of the infrared

light. Usually people use incremental encoder discs in conjunction with the

optical interrupter. To be specific, the incremental encoder discs have a series of

translucent lines that are etched into an opaque surface. Whenever the opaque

portion of the disc is inside of the proximity of the optical interrupter, there is no

infra red light that gets to the receiver. When the translucent portion of the disc is

between the two parts of the optical encoder, some infra red light gets to the

receiver. One can easily use this to his or her advantage by making the

translucent portions into thin lines that stand for certain discrete positions that the

25


stand can be at. For our setup, we would permanently attach the incremental

encoder disc to the stand. The optical interrupter would be mounted so as to

allow the encoder disc to be equidistantly between the transmitter and receiver.

As the shaft rotates, the disc rotates and lines in the disc rotate as well.

26


4 Feasibility Assessment

As a result of brainstorming and initial research, multiple concepts were

created for each of the design components. All of these concepts were

submitted for a feasibility assessment. The objective of the feasibility assessment

was to understand what was involved with each concept and decide which

concept had the highest probability of success. Each concept was evaluated on

the feasibility of its’ technical, economic, scheduling and performance aspects.

Each concept was assigned a rating between -, 0 and + for each of the attributes.

A score of 0 was a representation of a concept grading the same as the baseline.

A score of - represents a design that is slightly worse that the baseline design

and + represents a design that is an improvement over the baseline design. A

concept that received a - meant that it had very low feasibility. These parameters

were used to judge the concepts. Afterwards, we described the feasibility of the

designs in more detail. The discussion took on four aspects:

1. Performance Feasibility

2. Economic Feasibility

3. Technical Feasibility

4. Schedule Feasibility

The following sections present the feasibility for each of the design component

concepts.

4.1 The Stand

The first design component that we performed feasibility assessment on

was the most important component in the design. Because of this, we put the

most effort into this feasibility assessment, as can be seen by the number of

attributes used in the Pugh Analysis.

27


4.1.1 Stand Concepts:

Baseline Concept: Stationary Stand

A: Pneumatic Cylinder/Handle

B: Hanging Box /Trolley

C: Rotating Table

D: Pneumatic table movement/Pneumatic Stand

4.1.2 Attributes:1. Horizontal Movement

2. Vertical Movement

3. Radial Movement

4. Smoothness of operation

5. Stability

6. Repeatability

7. User-friendly

8. Ability to support weight

9. Cost-efficient

10.Ease of setup

11.Ease of control

12.Ease of build

28


4.1.3 Level of Attainment Analysis

Attribute A B C D

1 0 + 0 +

2 + 0 0 +

3 + 0 + 0

4 + 0 + +

5 - - - -

6 + + + +

7 + + + +

8 0 - 0 0

9 - - - -

10 0 - 0 0

11 + 0 + +

12 - - - -

Table 3 Pugh Analysis of The Test Stands: Baseline = Stationary Stand

As one can see from the Pugh analysis in Table 3, there was a tie in

feasibility between concepts A & D: the two pneumatic stands. To take care of

this, we decided to go through another round of Pugh Analysis. This time, we

decided to reduce the amount of concepts to only A & D and reduce the

attributes to the most important ones. This more specific Pugh analysis can be

seen in Table 4. We agreed that the following attributes were most important:

4.1.4 Critical/Important Attribute List1. Horizontal Movement

2. Vertical Movement

3. Radial Movement

29


4. Smoothness of operation

5. Stability

6. Cost-efficient

7. Ability to support weight

8. Cost-efficient

4.1.5 Second Level of Attainment Analysis

A D

1 0 +

2 + +

3 + 0

4 + +

5 - -

6 - -

7 0 0

8 + +

Table 4 Second Pugh Analysis of The Test Stands: Baseline = Stationary Stand

Again, there was no clear winner, so we decided to go further into the

analysis. We considered all the aspects of assessment as were discussed

beforehand. Seeing as we had already ruled out two of the concepts, we decided

to only analyze the two pneumatic stands.

4.1.6 Performance FeasibilityBoth of these designs require the use of pneumatic cylinders. The first

concept requires only two cylinders, while the second requires three. Seeing as

we decided to use a valve bank, this was not a true problem. The main problem

was that of the pressure required.

30


After talking with an industrial representative, we found that all of the

pneumatic components would be able to run properly on 60-80 psi, a level that is

usually found in laboratories. While we were there, though, the representative

brought up a problem that we had not thought of yet.

The problem was that putting a table on a pneumatic cylinder introduces

quite a bit of vibration when the cylinder gets to its two end points. This is due to

the fact that the cylinder operates, on a base level, with two mechanical stop

points. When these stop points are hit, the system comes to an abrupt stop and,

as a result, has quite a bit of vibration. We would be able to combat this by

making the cylinder double acting, in which both the exhaust and inlet ports

would have air pressure sent through them. In this setup, as one slowly reduces

the pressure on one side, one can either slowly speed up or slow down the

system. Still, there would be some vibration. Still, the other setup is mainly

hands-on and can also have quite a bit of vibration, depending on how hard the

technician swings it. However, one can handle this kind of vibration, seeing as

this only affects the performance of a single pipette. The vibration from the table,

however, would affect the calibrator, which would effect all future calibrations.

Thus, in this assessment, we decided that the concept of the manually moved

stand would be the best.

4.1.7 Economic FeasibilityAs was said before, both setups center on the pneumatic cylinders

Therefore, each of the designs have the same base cost for the vertically and

radial moving cylinder that holds the pipette and the other cylinder. The main

difference will be in the cost of the pneumatically controlled table.

When we talked to the pneumatic representative, we found that a common

table setup, including pressure control, tracks and sensors, would cost in a range

from $200-$300. This would consume most of our budget, leaving little room for

expenses that may come up later in the design. The manually controlled setup,

however, would have a main cost of bearings so that the setup can rotate

properly without wearing out the shaft of the pneumatic cylinder. The cost for this

31


is much less than that of the table setup. Thus, the manually controlled setup has

the definitive advantage in this feasibility, as well.

4.1.8 Technical FeasibilityIn this form of feasibility, we assessed how well we could apply our

knowledge to creating a working component. For the automated setup, we would

have to know how to machine a serviceable track from extruded metal so as to

reduce costs. This is a very rudimentary process, so we could easily perform this

task. Also, we would have to create a form of locomotion for the table, most likely

through wheels that would run on the track. We were fairly unclear as to how to

do this, so our knowledge in this aspect was lacking. Finally, we would have to

find a way to smoothly actuate both cylinders. We had done some research on

this and, with the help of our Mechanical Engineering Advisor, Professor Wellin,

and the pneumatic representative; we felt that we had a solid base of knowledge

from which we could easily control the system. When it came to the manual

setup, we had to know how to move the main cylinder manually. Seeing as this

will be a simple setup in which the cylinder will move with the help of bearings in

the table on which it stands, this would not be too hard for our level of

knowledge. As per the actuation of the cylinder, it would be the same as the

automated setup, but we would only have to control one piston, making it easier

as a whole. Again, the manual setup has the advantage in the feasibility

assessment.

4.1.9 Schedule FeasibilitySeeing as both designs are quite alike, the time schedules for the two

setups will also be similar. However, as was talked about in the Technical

Feasibility, we would have to do more machining for the automated setup,

creating a longer time schedule for setup. Also, the automated setup would have

to have extra programming and sensors to control the pneumatic cylinder on

which the table stands. This would also increase the time schedule for setup.

Seeing as we need to concentrate more on improving the setup than creating the

32


initial setup, it would be best if we had as little initial setup time as is possible.

Thus, the manual setup has the time advantage.

4.1.10 Final DecisionAfter going through all four forms of feasibility assessment, we can

conclude that the manual setup is the best for what our project.

4.2 Plunger Depression

This design component was a very important component in the design.

After all, if the pipette plunger cannot be depressed, one cannot transport fluid

from the vial to the calibrator. However, this setup is fairly simple, so we didn’t

have to account for too many attributes, as can be seen in the Pugh Analysis in

Table 5.

4.2.1 Plunger Depression Attributes:

1. Repeatability

2. Two stokes

3. Accuracy I force/distance

4. Ease of replacement

5. Ease of setup

6. Ease of control

4.2.2 Concepts: Baseline = Pneumatic Cylinder

A. Stepper motor with a lead screw

B. Spring loaded actuation

33



Attribute A B

1 0 -

2 0 -

3 + -

4 - +

5 - +

6 - -

Table 5 Pugh Analysis of Plunger Depression: Baseline = Pneumatic Cylinder

As one can see from the Pugh Analysis, the baseline concept was the

winning concept. In order to reinforce this finding, we went through the four steps

of feasibility assessment.

4.2.4 Performance FeasibilityWhen we looked at the concepts, we decided right away that the spring-

loaded actuation was not feasible. From a mechanical engineering viewpoint,

whenever a spring is included in the system, there are many variances that come

into play. Also, any performance from the system will be fairly rough due to the

fact that the springs may not move unless a certain load is achieved, reducing

the gradual nature of the actuation. Seeing as our experimentation has

concluded that gradual actuation is preferred over rough actuation, we decided

that this concept isn’t feasible from a performance standpoint.

Afterward, we compared the pneumatic cylinder to the stepper motor.

When it comes to the precision of movement, the stepper motor has the

advantage. After all, the stepper has a system of discrete steps that, depending

on the controller, can be controlled to an accuracy of 1/64 of a step, or about

34


1/32 of a degree. The true resolution, however, depends on the number of

threads per inch on the lead screw. Seeing as this parameter can be rather

small, this is not a problem.

When it comes to the cylinder, our control of the actuation is through force

instead of length measurement. For our means, we can control this parameter by

finding the two pressures needed to get to each level of actuation. After

experimentation, we found two values that would work for all models. This

method of actuation is preferable, seeing as the pipettes may not be mounted the

same way for each case. By using force stops, we can ignore differences in

length. We can do this with the stepper as well, but a force sensor will need to be

added to the design. Therefore, the slight advantage for performance goes to the

stepper motor.

4.2.5 Economic FeasibilityFor this case, we decided to create a miniature Bill of Materials so as to

make a more concrete analysis of our design. The approximate costs are listed in

Table 6 for the pneumatic system, and Table 7 for the stepper motor system.

Part Qty Cost

Total

Cost

Cylinder 1 ~$35 ~35

Regulators 2 ~$10 ~20

Switch Between

Regulators 1 ~$5 ~5

Total ~$60

Table 6 Estimated Cost of Pneumatic System

35


Part Qty Cost

Total

Cost

Stepper Motor 1 ~$20 ~$20

Force Sensor 1 ~$25 ~$25

Stepper Controller 1 ~$5 ~$5

Lead Screw 1 ~$10 ~$10

Total ~$60

Table 7 Estimated Cost of Stepper Motor System

As one can see, there is no clear advantage to either side. The only

advantage that one could possibly think of would be the fact that the pneumatic

system would be able to be bought all from the same supplier, making it possible

to get bulk discounts.

4.2.6 Technical FeasibilityIn this form of feasibility assessment, we thought not only about how much

we knew about the subjects, but also about the simplicity of the design. When it

comes to knowledge of the subjects, most of the team has had no real

experience with either pneumatic cylinders or stepper motors. The team leader,

though, has had extensive experience with use of stepper motors in robotic

design. Also, some of our advisors are knowledgeable about the use of stepper

motors. On the other hand, the team has advisors that are very knowledgeable

about pneumatics and all of the principles of pneumatic use have been covered

in the Mechanical Engineering syllabus.

When it comes to the simplicity of the design, however, the pneumatic

system has the clear advantage. One merely needs to attach tubing to the

regulators; the switch and the cylinder to do most of the setup. The stepper

setup, however, tends to have a more complex setup. This is due to the fact that

one has to constrain a nut that is on the lead screw, so that the nut moves

vertically instead of having radial movement with the rotating screw. Thus, when

we finished analyzing this feasibility, we found that the pneumatic setup had the

advantage.

36


4.2.7 Schedule FeasibilityAs was said in the technical assessment, the setup for the pneumatic

system will be much simpler. This is important, seeing as we need to limit the

initial setup time as much as possible to increase the time that can be spent on

improving the system. Seeing as a simpler setup decreases setup time, we can

say that the Pneumatic system has the clear advantage.

4.2.8 Final DecisionAfter going through all four forms of feasibility assessment, we can

conclude that the pneumatic setup is the best for what our project.

4.3 The Micro-controllerThis design component was a very important component in the design.

This component would keep track of all the actions and, depending on state of

the system, would tell the system to perform certain actions. We have taken an

account of four commonly used micro-controllers for our Pugh Analysis.

4.3.1 Micro-controller Concepts: Baseline Concept: PIC Micro

A. 8051

B. Basic stamp-2

C. DIOS

4.3.2 Attributes:1. Input/outputs

2. Applicability of code

3. Compatibility with PC

4. Ease of programming

5. Clock speed

6. Memory

7. Voltage requirement (small?)

37


8. Documentation on controller

9. Knowledge of controller

10.Cost

11.Cost of accessories


Attribute A B C

1 - - 0

2 0 - 0

3 0 0 +

4 0 + +

5 + 0 +

6 0 0 -

7 0 0 0

8 0 0 +

9 - + 0

10 0 - -

11 0 - +

Table 8 Pugh Analysis of Micro controller: Baseline = PIC Micro

As one can see from the Pugh Analysis in Table 8, the DIOS micro-

controller was the winning concept overall. Also, one can see that the 8051 and

PicMicro micro-controllers were about equal. To further understand why each

concept was feasible or not, we performed the four types of Feasibility

Assessment.

4.3.4 Performance FeasibilityWhen it comes to interfacing with a PC, all of the micro-controllers start off

with an equal footing. However, certain micro-controllers, such as the 8051 and

38


the PicMicro, need to have a serial communications port added on to a custom-

made breadboard in order to properly communicate with the computer. The Basic

Stamp and DIOS, however, both have readily available and in-stock breadboards

that have the capability for serial communication already built in. However, the

DIOS controller board has the unique advantage of direct solenoid/servo control

from the board.

When it comes to the amount of I/O pins, the more the better, seeing as

more pins means more commands that can be sent out. The PicMicro and DIOS

both have up to 40 pins, around 32 of which are programmable. The other

concepts have less total pins and, therefore, less I/O pins. Thus, the team found

that the DIOS had the largest advantage in this form of feasibility.

4.3.5 Economic FeasibilityWhen it comes to the price of the controller alone, the 8051 Micro

controllers are much cheaper than Basic Stamp or DIOS micro-controllers. In

fact, their prices are comparable with PIC micro controller. Still, this is not the

only form of cost that the system can have.

There is also the cost of accessories for the system. In this case, the 8051

and the PicMicro again have equivalent prices. The Basic Stamp, being a

Parralax product, has very expensive accessories when compared to the other

micro-controllers. Finally, the cost of accessories for the DIOS micro-controller is

relatively cheap when compared to the others. Seeing as we will have to add a

fair number of accessories to the micro-controller, we can say that the DIOS,

8051 and PicMicro are on almost equivalent footing.

4.3.6 Technical FeasibilityOne of the first attributes that come to mind when thinking of Technical

Feasibility would definitely be the ease of programming. Seeing as the team

leader has had extensive experience in programming systems with the Basic

Stamp, the team decided that this would be one of the easiest micro-controllers

to program. Still, the DIOS micro-controller also works with the Basic language.

39


Therefore, the DIOS micro-controller could also easily be programmed. The other

micro-controllers have a base language of Assembly, a language of which the

Electrical Engineers had a good amount of experience, but not much on system-

level programming.

Another attribute to consider would be the amount of documentation

available for the micro-controller. All of the micro-controllers have some

documentation, including books in the library. Still, the DIOS has an extensive

web community behind it that is willing to give support to DIOS users free of

charge. Therefore, one could say that, all in all, the DIOS micro-controller has the

advantage.

4.3.7 Schedule FeasibilityAs was said before, both the DIOS and the Basic Stamp had readily made

carrier boards that could do a majority of the things we wanted to do. Seeing as,

for the 8051 and the PicMicro, the team would have to modify a breadboard with

all sorts of components, each which would have to be purchased with a lead

time, one can easily see that the time for setting up the controllers is much longer

for the 8051 and the PicMicro.

When it comes to programming time, the DIOS and Basic Stamp have

very simple commands and the team leader knows most of the commands that

would need to be used in any functionality. Seeing as not all the commands were

known for the 8051 and the PicMicro, the team would have to lose valuable time

learning how to program the controller. Thus, in this form of assessment, the

DIOS and the Basic Stamp are tied.

4.3.8 Final DecisionAs one can see in the four forms of feasibility assessment, the DIOS is the

clear winner for the micro-controller.

40


4.4 Sensors for Vertical TrackingIn order to move the pipette from one place to another, one needs to clear

any objects that lie in its path. In order to keep track of whether the pipette is high

enough or not, one needs to install sensors. In the case of pneumatics, there are

a few sensors that are accepted as the industry standards. We chose these

sensors for the feasibility assessment.

4.4.1 Concepts for Vertical Tracking:Baseline Concept: Hall Effect

A. Reed Switch

B. Magneto Resistive Device

4.4.2 Vertical Tracking Attributes:1. Send signal to controller (feedback)

2. Easily mounted

3. Cost

4. Resolution/accuracy

5. Voltage/current needs

6. Simplicity of use

7. Knowledge of sensor


Concept A B

1 0 -

2 0 -

3 + -

4 - -

5 0 0

6 + -

7 0 -

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Table 9 Pugh Analysis of Vertical Tracking Sensors: Baseline = Hall Effect

By looking at Table 9, one would think that the reed switch would be the

most feasible concept. This will change, however, once we go further in-depth in

the feasibility assessment.

4.4.4 Performance FeasibilityWhen it comes to performance, the reed switch has a clear disadvantage.

The switch activates when a strong enough magnetic field is about ¼ of an inch

away and deactivates when the field goes about ½ of an inch away. This is not

very good resolution at all, especially seeing as how the pipette requires a higher

level of accuracy due to the need for the tip to go exactly into the fluid and not go

too high or too low. Thus, the reed switch is not very viable.

The Hall effect sensor and the Magneto-resistive Device both have a

better accuracy than the reed switch, but the two devices operate in different

ways. The hall effect sensor senses if a magnetic field of a certain predetermined

strength is present or not. If the field is any weaker than the predetermined

strength, the sensor will not pick it up. This makes it so the sensor doesn’t pick

up the magnet until it is right next to the sensor.

The Magneto-resistive Device, on the other hand, is not a proximity sensor

at all. This device measures the change in a magnetic field. Thus, it can keep

track of how far away a magnet is and how fast it is moving. The main problem is

that of the speed of the signal. When it sends out a signal, it takes a while to go

through its entire range and for the device to interpret this signal. Thus, the

resolution of position is not that good for the Magneto-resistive Device. Thus, one

can say that the Hall Effect sensor would be most feasible in this setup.

4.4.5 Economic FeasibilityAll of the sensors are not very expensive. In addition, they can be

mounted and attached to the micro-controller in almost the same way. Therefore,

one could say that, unless the budget for the project was to be near its limit, one

42


could choose either option at an almost equivalent economic feasibility. If one

had to choose an option that was most feasible, however, the reed switch would

be the obvious choice, as one can see from the Pugh Analysis.

4.4.6 Technical and Schedule FeasibilitySeeing as most of the team has worked with basic sensors and controls,

none of these sensors should be outside of the expertise of the team members.

However, the least easily set up option would be the Magneto-resistive Device.

This is due to the fact that, instead of sending out a simple binary signal for the

user to read, the user has to make some sort of setup to utilize the change in

resistance in the MRD. One of the most common ways to do this is to create an

RC circuit by using a common capacitor in conjunction with the MRD. Then, one

can calculate the RC time constant, find several known position for certain time

constants, and then linearly interpolate the data to find the positions for the RC

time constants that one receives from the circuit. As one can see, this setup

takes much more effort than the others, so this is the least feasible option, both in

expertise and time taken to set it up.

4.4.7 Final Decision

After going through all four forms of feasibility assessment, we see that

there is a tie between the Reed Switch and the Hall Effect Sensor as per how

many forms of feasibility they were best in. However, for our project, the

performance is the most important aspect of the design, at least as sensors go.

Thus, one can say that the Hall Effect Sensor is the most feasible option for our

setup.

43


4.5 Radial Movement SensorsThis component keeps track of the turning of the stand. Depending on the

readout from the sensor, one can see if the pipette is over the vial or over the

calibrator. From this, the micro-controller can tell the system to perform a certain

set of actions that is suitable for this position. Therefore, we had to be careful

when we performed the Pugh Analysis shown in Table 10.

4.5.1 Concepts for radial tracking:

Baseline Concept: Encoder disk and optical interrupter

A. IRPD (Infrared Proximity Device/Detector)

B. Sonar

C.Potentiometer

D.Hair trigger switch

4.5.2 Attributes:1. Cost

2. Accuracy/resolution

3. Feedback

4. Ease of mounting

5. Simplicity of use

6. Knowledge of sensor


Attribute A B C D

1 + - 0 +

2 - - 0 -

3 0 - + 0

4 + - + +

5 0 - - +

6 0 0 - 0

Table 10 Pugh Analysis of Sensors: Baseline = Optical Interrupter Setup

44


According to this analysis, the hair trigger switch is the winner. Still, as

was shown in the last feasibility assessment, this does not always show what is

the true winner. Therefore, we performed the four types of feasibility assessment

again.

4.5.4 Performance FeasibilityThe IRPD and hair trigger switches both share a common problem: that of

resolution. For the IRPD, the range that it covers is about two inches, with much

variability that can occur with the sensing. The hair trigger sensor also has a two-

inch range, but the range is confined to the trigger on the switch. Seeing as the

vials are less than an inch in diameter apiece, these ranges in sensing are not

acceptable. Therefore, if the sensor is triggered at a distance of 1 ½ inches

instead of the possible 2 inch range, the tip of the pipette would likely miss its

mark.

When it comes to sonar, there is one key problem. This problem is the fact

that once an object gets within the range of about one inch, the sonar sensor no

longer notices it. This is not suitable for our system, seeing as our design would

need to have the sensor close to the object to save space in the design.

The potentiometer and the optical interrupter both have very accurate

sensing apparatus. The resistive film in the potentiometer lets one track the

position very well with RC Time Constants and linear interpolation. The optical

interrupter’s encoder disk lets one instantly know when one is at a reference

point. Either way, they both do the job well.

4.5.5 Economic FeasibilityAs one could see from the Pugh Analysis, the cheapest of the sensors are

the IRPD and the hair trigger sensors. To be specific, the hair-trigger sensor is

the least expensive of them all. When it comes to the IRPD, however, it is not

much less expensive than the optical interrupter setup.

45


As per the sonar, not only is it the most expensive, but experience has

shown that they are very temperamental and tend to need to be replaced

regularly. Thus, this is far from a good choice for our system.

4.5.6 Technical FeasibilityWhen it comes to simplicity of use, one can’t get more simplistic than the

switch. After all, it is purely a physical touch sensor with binary output. The IRPD

is in the same vein; only it is a light wave sensor.

The sonar can be controlled with the proper conversion factor, either to

inches or mm. Still, as was said before, the sensor is quite temperamental, so

use of this sensor tends to give the user improper data that must be adjusted

each time a new type of error is introduced.

When it comes to the potentiometer, one has to figure out the RC Time

constants for certain positions and these Time constants change as the

capacitors either wear out or are replaced. Thus, it is fairly hard to keep track of.

The optical interrupter has a physical encoder disk that has lines etched

into it that are fixed in place. Thus, once one has mounted the encoder disk, one

no longer has to worry about adjusting for position error.

4.5.7 Schedule FeasibilityAll of the parts have to be mounted. The fastest mountings will be for the

IRPD and the switch. The second fastest would likely be sonar, seeing as one

also merely needs to mount it to be in place, but one also has to take time to find

the RC Time Constants. Third would be the potentiometer, which one has to

mount the shaft of directly to the cylinder. Lastly, the slowest to mount would be

the optical encoder, seeing as one has to mount the encoder disk to the cylinder

and then mount the mouth of the optical encoder around the disk.

When it comes to time spent correcting the errors in the system, the least

time would be spent on the optical encoder, seeing as it has very little ability to

have variance in it. The other sensors, however, would have plenty of time spent

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correcting the errors, perhaps even more than the time saved on mounting. Thus,

the team decided that the optical encoder would be the most feasible.

4.5.8 Final Decision

After looking through all forms of feasibility assessment, we found that the

optical encoder setup was the most feasible.

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5 Specifications, Analysis and Synthesis5.1 Mechanical Analysis & Synthesis5.1.1 Problem Statement

During the calibration of a pipette there are many factors that affect the

precise calibration of the pipette. Our goal is to minimize the factors that are

causing the error in the calibration.

5.1.2 Known InformationThe colorimetric or photometric method involves the analysis of volumes of diluted dye

in a cell of known path length. According to the Beer- Lambert Relationship,if a beam of

monochromatic light passes through homogeneous solutions of equal pathlength,the

absorbance measured is proportional to the dye concentration.So,with this in mind, an

unknown volume of dye can be pipetted into a known volume of diluent,the resulting dye

concentration can be measured photometrically, and the volume can be calculated.

There are many techniques and tips available that will optimize pipetting performance

and increase the reproducibility of results.

1. The equipment

1. Tips – It is advocated that only high quality tips, which optimize the pipette’s

performance, be used. A high quality tip is one that has a smooth uniform interior

with straight even sides that prevents the retention of liquids and minimizes

surface wetting. Also, the tip should have a clean, hydrophobic surface and a

perfectly centered opening in order to ensure the complete dispensing of the

sample.

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2. Liquid viscosity – since the pipette was originally factory calibrated using water,

any liquid that has viscosity higher or lower than water will impact the volume

dispensed.

2. The operator

1. Technique

a) Position – Pipette should be held vertical during the aspiration of liquids.

Holding a pipette 30deg. off vertical can cause as much as 0.7% more

liquid to be aspirated due to the impact of hydrostatic pressure.

b) Pre – Wetting /Pre – Rinsing Tips- Failing to pre-wet tips can cause

inconsistency between samples since liquid in the initial samples adhere to

the inside surfaces of the pipette tip, but liquid from later samples does

not. Also, if a new volume is dialed in on pipette’s micrometer, better

results will receive at the new volume by taking the old tip off and placing

a new one on the shaft before commence pipetting.

c) Release of Plunger – Releasing the plunger abruptly can cause liquid to

be bumped inside the pipette during a liquid transfer application. This can

cause liquid to accumulate inside the instrument which in turn can be

transferred to other samples causing variability in sample volume and the

potential for cross contamination.

d) Immersion Depth- The pipette tip should only be inserted into the vessel

containing the liquid to be transferred about 1-3mm. If the tip is immersed

beyond this, the results could be erroneously high.

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e) Thermal conductance- Thermal energy can be transferred from the

operator’s hand to the air within the pipette (dead air) or even to the

internal components themselves. This can have a dramatic impact on the

amount of liquid dispensed due to effects of expansion and/ or contraction.

To lessen this effect, it is recommended that some type of thermally

insulated gloves like latex of cloth be worn.

2. Pipette micrometer setting – It is important to avoid significantly over dialing or

under dialing the recommended range of pipette. Volume delivery performance

may change radically and may become completely undefined.

3. The Environment

a) Temperature – The volume delivery performance specifications of

pipettes have been referenced by most manufactures at room temperature

which is defined as (20- 25) deg.Celsius.Any deviation from this

specification can affect the amount of liquid dispensed due to the

expansion or contraction of the internal components.

b) Barometric Pressure – Pressure is reduced by 1.06” Hg for every 1000’

of elevation, however, barometric pressure has only a small effect on the

density formula, so the error encountered is not correcting for elevation is

often ignored.

c) Relative humidity – This is the percentage of moisture in the air at a

measured dry bulb temperature compared to the amount of moisture that

the air can hold at that temperature if the air is 100%saturated. Under dry

conditions, which are defined as less than 30% RH, it is extremely

50


difficult to ensure an accurate measurement due to the rapid evaporation

rate. Conversely, excessive humidity, which is defined as greater than

75%, can cause a measurement to be erroneously high due to

condensation. Therefore, generally accepted guidelines for pipette volume

delivery specify that relative humidity be maintained within the range of

45%-75%.

Concerning the operator, there are many factors in proper pipette techniques

that play a major role in the calibration process. Factors that the operator have

control of include the position of the pipette, pre-wetting the tips, release of the

plunger, immersion depth, and the thermal conductance.

The environment is also a factor that affects the calibration of the pipette

and such factors include vibration, evaporation, and temperature. All materials

involved in the photometric must be at the same temperature as not to get any

temperature gradients. Let the dye solutions, spectrophotometer, pipette, tips,

etc. reach thermal equilibrium at room temperature overnight if possible to make

results more accurate. Vibration creates air within the solution and can affect the

calibration; therefore vibration is a concern of the system.

5.1.3 Desired InformationDuring the pipette calibration the goal is to figure out the largest error factor

and then once that is taken care of work the way down as to minimize all errors

and make the calibration more precise. The largest error factor right now is the

“speed” at which the plunger is actuated. Some information needed is the

amount of force to actuated the plunger at first stroke and clean out stroke.

5.1.4 AssumptionsThere are a few assumptions that need to be listed within the system. The

thermal equilibrium concern should be taken care of and by this one is to say

there is no need for a controlled environment for the temperature of the system.

The materials of the calibration should all be in the lab for at least a work day to

make sure the equipment is all at thermal equilibrium. The system can also

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ignore any hydrostatic pressures caused when the tip of the pipette is placed into

the test fluid. The pressure created during this process is so minimal that it can

be neglected. Another important assumption is that there is no reason to concern

the system with any evaporation concerns. The test vial will be very close to the

calibration device and therefore with the laboratory environment there should be

no issue of evaporation. The last assumption that is that the air supply in the lab

is going to be no less then fifty pounds per square inch, as to design the air

cylinders bore size around the supplied air pressure and the force required.

5.1.5 Data and AnalysisThe problem with the pipette is the human interference and therefore if

that can be diminished then the error may be able to also be diminished. In the

tables below the experiment was held using different types of strategies to

operate the pipette.

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Pipette Calibration Result

Oxford

Pipette

Range 10 - 100 uL

SN# 014756

8885-

500945 Average for 80 uLAccuracy +/-0.5 - +/-1uL 81.78571429

http://www.novamedpipcal.com/OxfordVar.htm Average for 10uL11.594

Reading (uL) Suck in/ Dispense/ Angle Actual Reading (uL) % Error Percent Error with

respect to averages

80 slow/slow/vertical 81.5 1.875 0.349344978

80 slow/fast/vertical 82 2.5 0.262008734

80 fast/fast/vertical 81.7 2.125 0.104803493

80 slow/slow/angle 81.3 1.625 0.593886463

80 slow/fast/angle 82.1 2.625 0.384279476

80 fast/slow/angle 81.9 2.375 0.139737991

80 fast/fast/angle 82 2.5 0.262008734


10 fast/slow/vertical 11.52 15.2 0.63826117

10 slow/fast/vertical 11.55 15.5 0.379506641


10 slow/slow/angle 11.44 14.4 1.328273245

Comment: All reading were off by 1-2 uL

The pipette was out of tolerance.

Varying the technique did not seem to matter at all or where dispense the fluid at an

angle.

Table 11 Tests for the Oxford Brand Pipettes

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Fisherbrand pipette Average for 100 uLSN# N30775 99.725

Range 20 - 200 uL Average for 45 uLAccuracy 44.5075

Average for 20 uL19.7075

Reading (uL) Suck in/ Dispense/ Angle Actual Reading (uL) % Error Percent Error based on averages













Comment: No need to put the tip of the pipette at an angle, it

doesn’t make a difference. Readings were very close to expected

value.

Table 12 Tests for the Fisherbrand Pipette

As seen in Tables 11 and 12, there is much difference when the pipette is

actuated and released in different manners. In Table 13, the different pipettes

were tested to examine what amount of force was needed to actuate both levels

of the plunger.

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PipetteVolumetric

Setting Level 1 Level 2

Fisherbrand

(0-200) 20 uL 830g 2.4kg

50 uL 900g 2.4kg

100 uL 900g 2.5kg

150 uL 900g 2.4kg

200 uL 900g 2.4kg

Ranin (0-

20) 5 uL 900g 3.8kg

10 uL 700g 4kg

15 uL 700g 4kg

Oxford

(0-100) 10 uL 700g 2.8kg

50 uL 700g 2.5kg

100 uL 700g 2.6kg

Table 13 Force Requirements

The level one actuation is the amount of force used to inject the tip with

the appropriate amount of fluid and then eject the fluid. The level two is the clean

out stroke that is done at the time when all the substance is out of the tip and this

is just to ensure that all of the fluid is out of the tip. When the force was converted

to pounds of force it was calculated that approximately two pounds of force would

be required to actuate level one and to make sure that the entire clean out stroke

was actuated a force of eleven pounds will be used. The forces in Table 13 were

found using calibrated weights that were set on top of the pipette plunger and

with gravity constant after the suitable weight was on the pipette to actuate it; that

weight was the required force. Since the pipette requires two different forces to

run the calibration it would be a difficult process to accomplish with something

like a stepper motor. The first problem with using a stepper motor is that not only

would you need to have an output back to the motor to relay the force applied;

but as the volume of the pipette changes so does the range of motion of the first

stage actuation. This concludes that the best solution for the system is a

pneumatic one because not only can the pneumatics take care of the two

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different forces but it can also handle the different ranges of travel. The next

objective was to figure out what size pneumatic cylinder would be needed to

operate the pipette. With the assumption that the air supply would be no less

then 50 pounds per square inch, the equation below was used to find that a ¾”

bore cylinder would be appropriate for this application.

Clippard catalog series UDR-12 double acting cylinders will be appropriate

for both pneumatic cylinders. For the cylinder that is going to actuate the plunger

(cylinder #1) the range of actuation needs to be maximum distance of 1.14”

therefore the designed cylinder will have an actuation length of 2”. The cylinder

that will control the vertical movement of the system (cylinder #2) will have an

actuation length of 6” this will account for clearance of the lid of the calibration

device and capable of insertion of pipette tip into the test dye. According to

Clippard, the ¾” bore cylinders have a ¼” rod, which, also according to Clippard,

will handle a load of 190 pounds at a length of 5” until buckling occurs. The rod of

cylinder 2 will actuate to a length of 6” the buckling load is still far greater then

the applied load that it will experience. The maximum weight experienced by the

rods is nowhere in the range of 190 pounds.

To control the pneumatic cylinders there will be pneumatic valves with

regulators and speed control on each valve or inline with each valve. The speed

control is important to minimize vibration with control of the vertical motion and

most important to the actuation speed of the plunger. For this application the

system will use adjustable flow control valves that will be inline meter out needle

valves. The MFC series from Clippard is a good choice for the needle control

valves. There will be three different air pressures required in the system make

this possible there will have to be three air regulators that control each of the

pressures to the valves. The three regulators that are needed are all at different

ranges: 0 – 50 psi for the cylinder #2, 0 – 10 psi for cylinder #1 (first actuation),

and 0 – 30 psi for cylinder #1 (second actuation). The MAR series from the

Clippard catalog will work properly for all of these applications. The valves that

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will be electrically controlled are yet to be determined because the team may

have the valves donated to them, so the rest of the design may be completed

around these valves. For some specifications the valves will be controlled by 0 -

24 VDC and will have a manual actuation so it can be operated without the

electrical system.

5.1.6 Quality Review

After reading through this, I found that the report contains all of the facts

that we had covered over the quarter in a concise manner. Still, this contains

mostly information pertaining to the plunger actuation piston. If one were to think

of the piston that acts as a stand, one would have to take into effect the weight of

the setup, or:

You could then apply the force equation again, this time on the larger piston in

order to see if the pressure would be enough. I know from my experience with

the representatives from Roessler that the piston should be able to support up to

6 pounds if the cylinder rises 4-8 inches, which is enough to clear the colorimetric

calibrator. Speaking of which, we might want to add in the fact that the

colorimetric calibrator is 5 inches high by itself and 8 inches high with an opened

lid. Besides this, the analysis seems to be okay from a mechanical standpoint.

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5.2 Electrical Analysis5.2.1 Design Specifications:

The objective of this project is to fulfill all the requirements set forth by

Transcat. The design is to reduce variability and error induced by human

interaction with the pipettes and the calibration process.

5.2.2 Micro-controller Specifications: One RS232 serial port for PC communication (GUI)

At least 8 I/O ports

Low memory requirement (RAM size: 32 Bytes, EEPROM Size: 2K

Bytes)

Ease of programming (BASIC)

5.2.3 Sensor Specifications: 5V Logic

Piston sensors must be able to accurately sense piston position

Base sensors must be able to sense rotational position

Sensor for cover must be able to determine if cover is open or

closed

5.2.4 Power Supply Specifications: Must supply 5VDC and 24VDC

Must use 120VAC 60Hz single phase power

Must be able to handle a maximum current draw of 1A as valves runs on 1W

power.

5.2.5 Micro-controller5.2.5.1 Selection of Micro-controller

The Basic Stamp was chosen for this project due to its ease of use and

cost. The main constraint of the micro-controller is that we need RS232 serial

communication to a PC as well as at least eight input/output lines.

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Basic stamp 2 Module specs are:

24 pin DIP

Microcontroller: PIC16C57

Processor speed: 20 MHz

Program Execution Speed: 4000 instructions/sec.

RAM size: 32 Bytes (6I/O, 26 Variable)

EEPROM (Program) Size: 2K Bytes, 500 instructions

No. Of I/O pins: 16+ 2 Dedicated Serial

Voltage Requirements: 5-15 V

Current Draw @ 5V: 3mA Run /50uA Sleep

Source/Sink Current per I/0:20mA/25mA

Source/Sink Current per unit: 40mA/50mA per 8I/O pins

PBASIC Commands: 42

PC Programming Interface: Serial Port (9600 baud)

Windows Text Editor: Stampw.exe (v1.04 and up)

5.2.5.2 Integration with Electrical System

The electrical system currently has five inputs and three outputs. The

inputs are in the form of sensors. The three outputs are solenoid valves to

control air flow. For the micro-controller to work in this situation, we will need to

make a simple interface to make sure the sensors are on or off, with simply a 5V

or 0V digital input to the micro-controller. A different interface is required for the

output, as the solenoids valves require 24VDC and approximately 100mA,

sometimes up to 200mA when they actively switch. Since the micro-controller

can only provide 5VDC at around 20mA to an output pin, we will need to have a

power FET or a driver to provide the necessary power to the valves. Also

needed is a simple interface for RS232 communication with the PC. This serial

communication will provide the initialization for the micro-controller as well as

feedback and instructions to the user. The Stamp 2 Board has a built in RS232

59


interface, as well as room for an EEPROM, if additional memory is required as

the project progresses.

5.2.5.3 Inputs: Piston Up

Piston Down

Dye Position Sensor

Calibrator Position Sensor

Calibrator Cover Sensor

5.2.5.4 Outputs: Piston Up/Down

Stage 1 Pipette Activation

Stage 2 Pipette Activation

5.2.5.5 Serial: Receive Command to Begin Run from user

Send feedback messages to user

(i.e. “Please rotate the pipette to the Dye Position”)

Query user after each run if the wish to run again or end run

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6 Bill of Materials

Part QtyUnit Price

Total Price

DIOS Micro-controller 40 Pin 1 $24.95 $24.95DIOS Carrier Board #4 1 $39.95 $39.95DIOS Compiler 1 $0.00 $0.00TI SN754410 Solenoid Driver 1 $4.49 $4.49Power Supply Radio Shack 1 $17.99 $17.99Misc. Electronics 1 $10.00 $10.00Magnetic Proximity Sensor 1 $2.00 $2.00Hall Effect Sensor 2 $4.00 $8.00Optical Interrupter Sensor 1 $8.00 $8.00Adjustable Air Regulator 3 $5.00 $15.00Adjustable Flow Control 4 $32.30 $129.20Pneumatic Cylinder 7/8" Bore 1 $50.00 $50.00Pneumatic Cylinder 1 $30.00 $30.00Solenoid Valve 2-way 2 $18.00 $36.00Solenoid Valve 3-way 1 $25.00 $25.00Raw MaterialsShipping Costs 1 $30.00 $30.00Total $420.58

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Appendix A: System Schematic

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Appendix B: Electrical System

63


Appendix C: Flow Chart of System

64


65


66


Appendix D: Beer-Lambert’s Law

An unknown concentration can be found using a known absorbance of the

liquid and applying Beer's law. The Beer-Lambert law (or Beer's law) is the linear

relationship between absorbance and concentration of an absorbing species.

The general Beer-Lambert law is usually written as:

c = A/(a(lambda) * b)

Where a(lambda) is a wavelength-dependent absorptivity coefficient, b is

the path length, and c is the liquid concentration. There is also a blank of known

concentration and volume in the colorimeter. The system then uses the following

equation to find the unknown volume:

Concentration (test) x Volume (test) = Concentration (blank) x Volume (blank)

Appendix E: Hall Effect

The sensors used to detect the vertical position of the cylinder are called

Hall Effect sensors. The Hall effect is a phenomena of a voltage created

transversely to the current applied in a conductor, when there is a magnetic field

perpendicular to the current flow. The sensors respond to a presence or

interruption of a magnetic field by producing either an analog or digital output

proportional to the strength of the field.

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Appendix F: STAMP 2 MODULE

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Appendix E: Fishbone Diagram

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Error in Calibration Reading

Other Equipments

Environment

Calibration Method

Other Factors

The operator Pipette

Liquid viscosity

Tips Calibration with different

angles

Not smooth motion

Calibration with variable speed

Direct contact of sunlight

Pipette micrometer

setting

Pre – Wetting / Pre – Rinsing Tips

Release of Plunger

Immersion Depth

Position

Humidity

Barometric Pressure

Temperature

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