Engineering Sample 2

TV

[Company name] [Company address]

Executive Summary

The Project involves the Design & Development of the system to measure & control the Level of

Liquid in the tanks. There are numbers of the measurement techniques that can be used for the

measurement. But the technique of using the float arrangement with the valves can come out as

the most successful method due to its simplicity of design & very low installation cost. The

method utilizes the sensors that is mechanical in nature and utilizes the physical principle of the

buoyancy to get the input signal. The input signal is just the mechanical deflection that has been

further utilized and converted to the Electrical analogue signal using certain kind of the

transducers depending upon the range and the sensitivity of the measurement required.

The most important feature of this system is that it can be scaled on the practical grounds for the

tanks of smaller size like that of the water tanks on the top of the domestic/commercial buildings

as well as to the tanks of the giant size like the tanks to preserve the variety of oils and water

storage for the machines & Boilers in the Industries.

Background

In today’s industries when the optimization of the resources is required to be performed at each

and every level so that the work being done & the resources being utilized don’t go in vain at any

cost. Thus, the maximum pressure comes on the Quality Department which first of all points to

the Measurement & Metrology Department. It is always the duty of the Metrology &

Measurement department to keep itself updated and have a check on all the instrumentations and

the methods being used. Thus the major concern is with the cost and effectiveness of the

instruments being used and replacing those in case of any fault. This project is thus aimed at

providing the simple and the effective method to sort out the complexities involved in the

measurement of the level of liquid in the various types of tanks based in industries.

Scope

The task of developing a system that uses the basic and Fundamental Law of physics

(Archimedes Principle) for controlling the level of the liquid in the tanks is identified in practical

sense. The instruments based upon this principle are being used in many industries. The

difference lies in the use of the transducers. The mechanical signal collected from the primary

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sensor could be converted I to the analogue electrical signal in the number of ways. It depends

upon the choice of user and the expectations of the final result which type of the transducer is

selected. Some users prefer to get the output in the analogue form while the digital form is

preferred by some of those. Whatever method is selected the method of calibration is to be the

perfect one for the quality of results.

Design Summary

There will be a float having the spherical shape with the hollow body with a hinge joint at its top.

The radius of the ball will be calculated as per the requirement and the size of the tank. The arm

of the ball will be so that it will fall under the gravity if the force of buoyancy is not there. This

will ensure that the float will always be in contact with the surface of the liquid. The upward and

downward motion of the ball with the liquid level will produce some deflection in the form of

mechanical signals. These signals are then detected by the transducer. Here we will use the

potentiometer that has the variable voltage produced across it due to the deflection of the

pointing wire along it. This variable voltage will be an analogue signal coming out as an output

of the transducer and could be converted to the digital signal if required. There is an arrangement

of the linkages such that when the level of the ball reaches a specified limit the further upward

movement of the ball will cause a valve regulating the inflow pipe to shut off. This will stop the

inflow of the liquid. Further in order to get the pump shutoff a relay can be used that may control

the circuit of the pump and close it whenever the set range of current is induced.

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Table of Contents

Introduction...............................................................................................................5

Description of the Project.........................................................................................5

Implementation..........................................................................................................7

Division of Tasks.....................................................................................................10

Problems Faced......................................................................................................11

Sensor Selection & its Type....................................................................................12

Implementations of the Results in to the Measurement system...............................13

Hardware Configuration.........................................................................................15

Conclusion..............................................................................................................19

References...............................................................................................................20

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IntroductionThere are many applications where the liquid level in the tank is controlled by direct

involvement of the human beings in the task. Individuals personally are assigned with the task of

doing this. But, it is in actual the waste of time and resource even if it is done at very small level.

Even in the domestic front it is really not affordable for the individuals to just get the tanks kept

above the terrace checked for switching off or on the supply of the water. The system that we are

designing has its application at even that level for the reasonable price. The use of the Float is

quite inexpensive if just a small system, based on certain mechanical components is used for the

purpose.

Figure 1: The basic setup of the float valve.

It can be easily visualized that the level of the liquid decides the angle between the arm of the

float and the vertical.

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Description of the ProjectThe aim is to use the simple components for the sake of getting a mechanism that can be used for

the sake of the measurement of the liquid level wherever and whenever necessary. There are

number of the ways the float valve can be used to check the inflow. The selection among those

just depends upon the application. We basically require the system that is required to measure the

level of liquid in a tank having the height of about 10 meters and is kept in industry to store the

water that is to be further utilized for the supply to the condenser. The cross section of the tank is

circular in shape having the diameter of 2 m.

The aim is to get the alarm ring when the level of water reaches 2.5 meters, 4 meters, 6 meters,

7.5 meters & 9 meters. All these values are randomly selected and there must always exist the

scope of setting up and changing these values as per the requirement. Thus the details can be

tabulated in the table as below:

Level (m) Description

2.5 It is the level at which the water level is assumed to be at the level that

it cab started being used for the major applications. It actually

represents the level below which the shortage of water is supposed to

exist and it is used only for the minor applications and not for the

major ones.

4 The level has started growing up and has reached the satisfactory

level. But still the major applications cannot be operated for long

periods.

6 The water is now supposed to be sufficient enough to run all the major

machineries.

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7.5 Now the level reaches the value such that the usage can be made at

least for the 2-3 days. It also represents the first warning for the level

of the water.

9 It is the tank at its full and the level above it is to be kept free for the

installed arms and the mechanism of the controlling valves.

Implementation

Calculation of the Buoyant Force

Figure 2: The tank shows the partially submerged ball in the water with the setup of the device

on the top of the tank.

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Figure 3: Depiction of the force of Bouyancy

Let ρwdenote the density of the liquid inside the tank.

The mass of the object being submerged is assumed to be m.

Let ρbe the density of the material of the float.

From the law of Buoyancy, it is stated that the buoyant force on any object that being partially or

fully submerged in any liquid is equal to the Weight of Liquid Submerged in the magnitude. The

direction of this force will always be in the vertically upwards direction.

Let h, be the depth of the object submerged in the liquid.

Thus, force of gravity on the object, F g = mass X acceleration due to gravity

= Density X volume of the object X acceleration due

to gravity

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= ρ X 43

X π X R3 X g.

h

Figure 4 : Object under Bouyancy

If h is the depth of the object immersed in the liquid,

The buoyant force acting on the object = Weight of the liquid displaced

= ρwX (volume of the hemisphere of depth R – volume of the part of the body between the centre

of the sphere and the level of the liquid) X (acceleration due to gravity)

= ρw X ¿ – v] X g

The value of v is to be calculated using the geometry and the basic integral calculus;

Let at any depth, l from the center the radius of the small circle bounding the object is r.

Thus,

R

l

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Figure 5: The geometry below the centre

R2 = l2 + r2.

V = ∫0

R−h

π X r 2 X dl = ∫0

R−h

π X ( R2−l2 ) X dl

= π X [ 23

R3−h2 R+1/3h3]

Now for the body to float the Buoyant force must be equal to the weight of the object. If we

equate these equations we will get the relation between the density of the object and the density

of the liquid to keep the body floating even.

The interesting fact about this calculation is that though we are able to recognize the material of

the float to be used for a specific type of liquid, but it doesn’t have any influence of the level of

the liquid in the tank.

The proportion of the object above and below the liquid surface is always constant independent

of the level off the liquid in the tank.

Division of TasksAs there are number of sub systems associated with the task, each sub system can be kept as the

tasks.

First of all the objective is to select the correct sensing float so that the results obtained

are very precise & accurate with the minimum level of the deviations.

The mechanical assembly transmitting the signal must be strong, rugged, and sensitive as

well as friction free to transmit the required amplitude of the signal.

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Selection of the correct transducer for effective conversion of the mechanical signal in to

the electrical one.

Selection of the Relay for cutting off the pump circuit when required and a relay for the

alarm to be blown when the level reaches the particular benchmarks.

Keeping the level of the cost below the desired level.

Problems FacedSince the setup is to be used for the purpose that is related to the industrial requirements of the

setup, it has certain issues to be addressed for the proper functioning.

Vibration control: Due to the large size of the tank, the inflow rate is quite high. The

water comes and pours down in to the tank with a very high flow rate and this causes a

lot of movement and the disturbance in the liquid volume with amplitudes & frequencies

of the waves produced on the water surface. Greater the inflow rate is more will be the

turbulence and thus greater will be the probability of the vibration and the unwanted

signals sensed by the Float.

Installation of the Mechanical components at the top with the weight being as small as

possible. All the components must be highly sensitive and must transmit even the smaller

rise or fall in the level.

Making the setup more simple and versatile to be used by other industries.

Special maintenance requirements of the components for proper functioning. Like

greasing, tightening screws & alignment of the bearings and shafts.

Calibration of the output with the level of the water.

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Sensor Selection & its TypePerformance Test

A performance test for the sake of experimentation was performed in the tank of about 500

liters capacity with the scaled prototype having the smaller volume. The objective was to

verify the results with the reality that is quite easy to be measured in this case as well as to

now the deviation of the calibrated scale from the actual scale.

First of all the signals obtained are to be transmitted without any loss. The Readings of the

potentiometer are noted down and then compared with the readings of the actual level of the

tank. This is further used for the calibration purpose.

The table below shows the result for the experiment with the rise in level by 7 cm s in small

steps of I cm each. The variations of the output voltage obtained across the voltmeter have

been indicated

Table 1 : Experiment observations

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S No. Level(m) Voltage(V)

1 .01 1.1

2 .02 1.3

3 .03 1.489

4 .04 1.695

5 .05 1.903

6 .06 2.1

7 .07 2.287

Figure 6 : Potentiometer Setup

Figure 7 : Potentiometer with Float

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Implementations of the Results in to the Measurement systemThe scope of the results obtained is clearly understood after plotting it.

Level of the Liquid Voltage Read by the Voltmeter

0.01 1.1

0.02 1.3

0.03 1.489

0.04 1.695

0.05 1.903

0.06 2.1

0.07 2.287

The Results obtained showcase the linear variation between the variable

0 1 2 3 4 5 6 7 8 90

0.5

1

1.5

2

2.5

Series1Series3

The components on X axis are in m with the multiplication factor of 10 -2

There is only little bit of non-linearity observed in the diagram. That too arises due to the errors

of the sensing. These readings have been obtained when the measurement was performed at very

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small level. But the conditions used were quite harsh as that in the industry. Thus all these small

errors would get neglected when the system will be used for the major systems as the real case is.

Thus the calibration of the voltmeter which is our final output reflecting device is done as per the

deviations obtained in the table .But this time the values are to be selected as per the magnitudes

of the larger system.

Hardware ConfigurationThe control of the flow in to the tank can be directly controlled by the motion of the arm

having the float at its end. It is not even necessary to send the input from the system to

the actuators separately. The actuating system can be directly connected to the input

sensing system such that the value at which the flow rate is required to be stopped has to

match with the distance ratio of A:B so that the valve gets pushed down. There is also an

advantage that even if the electrical system breaks down completely, the measurement

can get altered but the controlling would be smoothly and independently handled by the

system. The overflow will always be prevented.

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Figure 8: The Actuator system

For the sake of the alarm at the specific levels that we have recogniozed there are two ways :

Switches can be used at each of those specified levels that directly take the input from the

mechanical sensor and ring the alarm when the level matches their value.

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Figure 9 : Limiting Switch Arrangements

Each of these limiting switches has a connection with the circuit of the alarm. As soon as

the level reaches that specified value, the circuit gets completed and the alarm rings.

The advantage of this method is that there is no need of the output coming from the

system which then with the help of the specially built actuator system will take the

controlling action.

There is also an advantage that even if the electrical system breaks down completely, the

measurement can get altered but the controlling would be smoothly and independently

handled by the system. The overflow will always be prevented.

At the end when the level reaches the value of the overflow of tank, the relay cuts off the

pump’ s connecting circuit. Thus the inflow stops at once.

Figure 10 : Relay to shut off the pump.

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The output signal of the system that is being used for the interpretation can be sued for

the controlling by creating the interface between the system and the actuators. But this

system requires greater efforts, would be more costly and would add to the cost

unnecessarily.

The Block Diagram that can be used to represent the developed measurement system is:

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Physical system .Water Tank with the capacity of about 31,415 Liters & height of about 10 m.

Sensing device. The mechanical Float connected with the arm free to rotate about an hinge present at the top of the tank.

Device used for conditioning the signal. The method is to make the arm connecting the float as much lengthier after the fulcrum as possible.

Transducer. The signal that is still in form of Mechanical displacement is converted to the Analogue Electrical Voltage by using a setup having the potentiometer and the Rheostat.

Analogue to Digital Converter. The required voltage signal is converted in to the digital form with the help of certain electronic devices.

ConclusionThe objective of creating a system that could be used to measure and control the level of the

liquid in a tank is achieved using a system that uses the Float connected at the end point of a

mechanical lever arm. This arm acts as the sensor and is based on the fundamental buoyancy

principle. The motion of the lever arm about the fulcrum is utilized as the measure of the

required physical parameter, the level of water. The variation of the output voltage comes out to

be approximately linear in variation with the input (water level). This further eases the problem.

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Computer. The digital signals can be easily understood by the computer and those are displayed on the screen.

References[1] Doebelin O. E & Manik D. N. Doebelin’s Measurement Sytem Tata Mc Graw Hill (2011).

[2] Morris A. S. Measurement & Instrumentation Principles. Butter Worth Heinemann, Linacre

House, Jordan (2001).

[3] Bolton W. Instrumentation & Control Systems. Linacre House, Jordan Hill, Oxford (2004).

[4] Langari R. & Morris A. S. Measurement & Instrumentation – Theory & Application.

Academic Press (2015).

Sources of Images

[1] Control of inflow of cold and hot water using float valve. Retrieved from

<http://www.practicaldiy.com/plumbing/water-supply/cold-water-tank-1.gif>

[2] The depiction of Force of Bouyancy & the gravitational force Retrieved from

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< http://images.tutorvista.com/cms/images/83/Buoyancy-force.

[3] Depiction of the working of Actuator using Float Valve. Retrieved from

< http://lamspeople.epfl.ch/kirrmann/Slides/PIDControl_files/ctl000601a1.gif>

[4] Arrangements of the Limiting Switches at various levels

< http://www.ibiblio.org/kuphaldt/electricCircuits/Digital/04227.png>

[5] Cut off Circuit of the pump with the help of Relay. Retrieved from

< http://www.reuk.co.uk/OtherImages/float-switch-circuit.jpg>

[6] Transducer in the form of Potentiometer

< http://sub.allaboutcircuits.com/images/00185.png>

Appendix

List of Figure

Figure 1: The basic setup of the float valve.

Figure 2: The tank shows the partially submerged ball in the water with the setup of the device

on the top of the tank.

Figure 3: Depiction of the force of Bouyancy

Figure 4 : Object under Bouyancy

Figure 5: The geometry below the centre

Figure 6 : Potentiometer Setup

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Figure 7 : Potentiometer with Float

Figure 8: The Actuator system

Figure 9 : Limiting Switch Arrangements

Figure 10 : Relay to shut off the pump.

List of Tables

Table 1 The Reading of the Experiment performed on a small water tank

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