msc lnstruments 2015

Performance Characteristics of Instruments

• Static Characteristics– Precision/Repeatability/Reproduciblity– Sensitivity/Responsivity– Resolution/Least count– Linearity– Stabilty and drift– Threshold– Dead Band and Hysteresis– Input Imedance– Output Impedance– Span & Range

Performance Characteristics of Instruments

• Dynamic Charcteristics– Speed of response– Fidelity– Bandwidth– Measurement lag/ dealy– Settling time– Dyanmic range– Time constant(time to reach 63.2% of Final

output)

Uncertainties in analytical measurements

• Precision of an analysis: Precision of an analytical measurement means –repeatability or reproducibility of the results of an experiment performed several times under the same conditions.

• Precision is measured by the standard deviation of replicate analysis.

Precision – Standard Deviation The smaller the standard deviation, the more precise

the analysis.• Standard Deviation

σ

• Xi = each individual reading in of n observations of the same variable.

• Precision(%) P= (σ / Xmean)100• Sometimes we define Xmean = µ

• Estimation of analytical precision: In practical analytical terms, the most efficient method for estimating precision of an analytical method is to use replicate analysis of randomly selected samples.

Precision …

• A very simple example:• 10 replicate measurements of Cr (µg/g) in a rock

sample are :247, 250, 249, 262, 245, 257, 246, 251,271, 248.

• The mean Cr (µg/g) = Xmean (µ )=252.6• The standard deviation SD( σ) = 8.3• Precision expressed in percentage, relative to

the mean P =(8.3/252.6)100= 3.3%• The Cr (µg/g) value in the sample = 253 + 3%

Accuracy• Accuracy=[Mod{actual value-measured mean

value}/actual value]*100• A very simple example:• 6 replicate laboratory measurements of iron

(µg/g) in samples of spinach standard are : 480, 510, 490, 470, 526, 473.

• The certified reference value of the standard is 550 + 20 (µg/g).

• The mean value of iron (µg/g) = 491.5• Precision = 4.5%• So, the observed value is 491 + 22.• Accuracy = ( mod(550 – 491))/ 550 ) *100 =

10.9%• So, even though precision may be good (4.5%),

the accuracy may be poor (11%).

Accuracy versus Precision(shooting at a target)

Not accurate or Precise Precise but NOT accurate

Accurate and NOT Precise Accurate AND Precise

Uncertainties in analytical measurements

• Errors in measurements– Gross errors: These depend upon care and vigilance

observed by the experimenter and can be minimized– Systematic errors: These are caused by inherent

shortcomings of instruments and components used in the system. They can be eliminated by applying correction factors

– Random Errors: These errors are due to sources and causes that can not be specified. They are uncontrollable and unavoidable. Statistical analysis can improve the measurement.

Errors in measurements• Gross Errors:• Lack of knowledge of instrument• Zero adjustment• Loading effects• Mirror parallax• Different operating conditions• Ware and tear of the instruments

Errors in measurements• Systematic Errors:

• Static and dynamic characteristic of the instruments.• Improper calibration of instruments.• Environmental effects on instuments• Instrument loading

Random Errors• The Source for these errors are fluctuations in supply Influence of RFIAir currentsMovements in surroundingsWeather change

Measurements:Basic Concepts

• Measurand• Bio potential, pressure, flow, dimensions, displacement (velocity,

acceleration, force), impedance, temperature, chemical concentrations

• Transducer• Transduction: convert one form of energy to another;

• Sensor: converts measurand to an electric signal

• Properties: minimize energy extracted, minimally invasive, respond only to form of energy present in measurand

Other definitions of Transducer• Mechanical transducer: They respond to

changes in physical conditions of a system and deliver output signal proportional to the measurand, but of different form and nature(non electrical output)

• Electrical Transducer: They respond to changes in physical conditions of a system and deliver output signal proportional to the measurand, which are by and large electrical in nature.

• Compound Transducers: Some transducer may have compound stages of transducers to increase the sensitivity (load cell)

• Range: limits between which the input can vary.

• Span: maximum value of the input minus the minimum value

• Eg: load cell for the measurement of forces: range of 0 to 50kN, span = 50kN

Performance :Range and Span

• Error = measured value – true value• Eg, if actual temperature is 24 deg C, and reading is 25

deg C, then error is +1 deg. If actual temperature is 26 deg C, error = -1deg.

Performance:Error

• Accuracy = extent to which the value indicated by a measurement system might be wrong.

• Summation of all possible errors, as well as accuracy to which the transducer has been calibrated, often expressed as a percentage of the full range value.

• Eg: +/- 5% of range. If range is 0 to 200degC, then the reading will be within +/-10degC of the true reading

Performance :Accuracy

• The relationship indicating how much output you get per unit input(=output/input). For example, a resistance thermometer may have a sensitivity of 0.5./degC

• Sometimes it also indicates the sensitivity of inputs other than that being measured, for example, environmental changes (eg, temperature changes or fluctuations in the main voltage power supply).

Performance: Sensitivity

Performance :Hysteresis error

Transducers might give different outputs from the same value of quantity depending on whether that value was reached by a continuously increasing or decreasing change. This effect is called hysteresis.

• Most transducers have a linear relationship between input and output

• Not true in general – error is defined as maximum difference from the straight line

• Different methods for the numerical expression of the nonlinearity error.

Performance :Nonlinearity Errors

Nonlinearity Errors using 1. End points 2. Best fit 3. Best fit through zero

• Repeatability: Ability to give the same output for repeated applications of the same input value.

• Stability: Ability to give the same output when used to measure a constant input over a period of time. Drift is the change in output that occurs over time (% of full range output)

• Zero drift: when zero input is applied.

Performance: Repeatability, Stability/Drift

• Dead band :Range of input values for which there is no output.

• Dead time: length of time from the application of an input until the output begins to respond and change.

Performance :Dead band

• If input varies continuously, output for some sensors may change in small steps (example: encoders).

• Resolution = smallest change in the input value that will produce an measurable change in the output.

Performance :Resolution

• Necessary to know loading effects, when the

sensor is interfaced with an electric circuit. • Inclusion of the sensor might significantly affect

the behavior of the system to which it is

connected.• Sensor can be connected either in series or in

parallel.

Performance :Output impedance

• Static = steady-state• Dynamic:– Response to step input• Response time (reach 95% of step)• Time constant (the 63.2% response time)• Rise time (time from 10% to 90 or 95% of

steady-state)• Settling time (time for output to settle to within

2% of steadystate)• These exact statistics may change slightly –

look them up on spec sheets.

Performance: Static and Dynamic Characteristics

Characteristics

• Displacement: how much something has been moved

• Position: where an object is with respect to a reference point

• Proximity: a form of position sensor, detect when an object is within some critical distance of the sensor (on/off)

Performance :Displacement, Position and Proximity

• Size of displacement (inches, millimeters,meters?)• Is displacement linear or angular?• Resolution required• Accuracy required• What material the measured object is made of (some sensors work only with ferromagnetic metals, some only with insulators)• Cost

Position sensorsHow do we select?

• Contact sensors: measured object touches the sensors • Non-contacting :no physical contact• Linear displacement contact: sensing shaft in direct contact with the object monitored. Displacement of this shaft monitored.• Angular displacement contact: the rotation of the shaft might drive, through gears, the rotation of the transducer.• Non-contacting sensors: change in air pressure, inductance or capacitors.

Main types

Potentiometers

• A resistance element with a sliding contact that can be moved over the length of the element.

• Can be used for linear or rotary displacements.• Displacement is converted into a potential

difference.• Rotary potentiometer: circular wire-wound track

(single turn or helical)• fixed (input)

Potentiometers

• Voltage between 1 and 3 is a fraction of Voltage between 1 and 2

which is the input voltage• Track has constant resistance per

unit length (or unit angle)• Output is proportional to angle

through which slider has moved.• An angular displacement can• be converted into a potential

difference

Resistive Sensors - Potentiometers

Translational and Rotational Potentiometers

Translational or angular displacement is proportional to resistance.

Taken from www.fyslab.hut.fi/kurssit/Tfy-3.441/ luennot/Luento3.pdf

Potentiometers

• Wire wound track: voltage output changes of one step per turn. If the potentiometer has N turns, then its resolution is 100/N (as a percentage).

• Resolution limited by the diameter of the wire used, typically ranges from 1.5mm to 0.5mm.

• Nonlinear errors: 0.1% to 1%• Track resistance: 20. to 200k .• Conductive plastic has better specs

Strain-Gauged Elements

Electrical resistance strain gauge• A metal wire, metal foil strip, or a strip of

semiconductor material, which is wafer like and can be stuck on surfaces like a postage stamp. When subject to strain, its resistance R, changes, with the fraction ΔR/R being proportional to strain(ε) as:

• (ΔR/R)/ε = G. G is called the gauge factor.

• Strain is (change in length/original length). The resistance change of a strain gauge is the change in length of the element to which the strain gauge is attached.

• Typical G: about 2.0 for metals, +/-100 for semiconductors

Resistive Sensors - Strain GagesResistance is related to length and area of cross-section of the resistor and resistivity of the material as

By taking logarithms and differentiating both sides, the equation becomes

Dimensional piezoresistance

Strain gauge component is related by poisson’s ratio ‘ν’ as

Resistive Sensors – Strain Gage

Gage Factor of a strain gage

G is a measure of sensitivity

Think of this as a Transfer Function!Þ Input is strainÞ Output is dR

Þ Put mercury strain gauge around an arm or chest to measure force of muscle contraction or respiration, respectively

Þ Used in prosthesis or neonatal apnea detection, respectively

Resistive Sensors - Strain Gauges

Strain gages are generally mounted on cantilevers and diaphragms and measure the deflection of these.More than one strain gage is generally used and the readout generally employs a bridge circuit.

Where can you use it in the body? E.g. prosthetic, or artificial hip/knew?

Strain Gage Mounting

Applications!Þ Surgical forcepsÞ Blood pressure

transducer (e.g. intracranial pressure

Þ Atomic force microscope

Bridge Circuits

Wheatstone’s Bridge

R-dR R+dR

R

Rf

Vs

RVo

Real Circuit and Sensor Interface

Load cellPrinciple

Principle of Load cell operation Load cells measure forces and moments by sensing

the deformation of elastic elements such as springs. Usually it comprises of two parts

the spring: deforms under the load (usually made of steel)

sensing element: measures the deformation (usually a strain gauge glued to the deforming element).

Load cell measurement accuracy is limited by hysteresis and creep, that can be minimized by using high-grade steel and labor intensive fabrication.

http://www.spl.ch/facilities/Test-Stand/Test-stand_load-cell.jpg

http://www.clipart.com/en/close-up?o=638353&memlevel=C&a=c&q=load&s=61&e=90&show=&c=&cid=&findincat=&g=&cc=&page=3

Strain gaugeswire

Metal foil

Semiconductor

Cantilevers

Circular shapes

U-springs

Strain gauges

• Gauge factor supplied by manufacturer, needs calibrations for samples in a batch.

• Known problem with strain gauges:• Resistance changes with both strain and temperature• Semiconductor strain gauges are much more sensitive to

temperature changes than metal gauges.• Some displacement sensors have strain gauges

attached to flexible elements of various shapes .• measure displacement or deformation of flexible element• (OK for linear displacements of about 1 to 30mm, error

about +/- 1% of full range).

Optical encoders• Encoder: a device that provides a digital output as a

result of linear or angular displacement.• Position encoders are of two types: incremental (changes

in position) vs. absolute encoders (actual)• Angular encoders :Beam of light passes through slots in

a disk and are detected by a light sensor. When the disc is rotated, a pulsed output is produced by the sensor, with the number of pulses being proportional to the angle through which the disc rotates.

• Angular rotation of disc (and of shaft rotating it) can be determined by the number of pulses produced since some reference position.

Optical encoders

• In practice three concentric tracks are used.

• Inner track is used to locate “home” position. Other two tracks, with suitable spacing, allow for the determination of direction.

• If 60 slots per revolution (360deg), then resolution

is 360/60 = 6deg.

• Optical encoders

• For example, the HEDS-5000 series from• Hewlett Packard, are supplied for• mounting on shafts and contain an LED• light source and a code wheel. Interface• integrated circuits are also available.

Hall effect sensors• When a beam of charged particles passes

through a magnetic force field, forces act on the particles and the beam is deflected from its straight line path.

• A current flowing in a conductor is like a beam of moving charges and thus can be deflected by a magnetic field.

• This effect, the Hall effect, was discovered• by E.R. Hall in 1879.

Hall effect sensors Electrons are deviated to

one side of the plate becomes negatively charged, and a transverse potential difference V develops.

• If a constant current source is used with a particular sensor, the Hall voltage is a measure of the magnetic flux density.

Inductive Sensors

An inductor is basically a coil of wire over a “core” (usually ferrous)

It responds to electric or magnetic fields

A transformer is made of at least two coils wound over the core: one is primary and another is secondary

Primary Secondary Displacement Sensor

Inductors and tranformers work only for ac signals

An interesting application: traffic signal

Beach comber!

Mine sweeper

Inductive displacement sensor (LVDT) I• A linear variable displacement transformer (LVDT) is a 3-

coil inductive transducer.– Mutual inductance between the

coils is changed as the position of a high permeability rod is moved between them :

– Secondary windings are connected in series opposition

– When the rod is centred, equal secondary voltages are induced, s.t. the output voltage is zero

)t(v)t(v)t(v21 SSout

),t(vk)t(v in1S1 )t(vk)t(v in2S2

S1

S2

Pvin(t)

vout(t)+

–

+

+

–

–

ferrite rod

Inductive displacement sensor (LVDT) II

– As the rod moves from the centre, as shown, k1 increases, while k2 decreases

– vout(t) is linearly related to the change in position of the rod

AC voltage source • range is limited by extent of coils • no moving parts

Example application : repetitive displacements in robotics

S1

S2

Pvin(t)

vout(t)+

–

+

+

–

–

Inductive Sensors - LVDT

LVDTLinear Variable

Differential Transformer

An LVDT is used as a sensitive displacement sensor: for example, in a cardiac assist device or a basic research project to study displacement produced by a contracting muscle.

Capacitive Sensors

e.g. An electrolytic capacitor is made of Aluminum evaporated on either side of a very thin plastic film (or electrolyte)

Electrolytic or ceramic capacitors are most common

Question: How can I detect small change in capacitance?

How does an elevator keypad or certain contact less computer keypads work?

Capacitive SensorsOther Configurations

c. Differential Mode

b. Variable Dielectric Modea. Variable Area Mode

Piezoelectric Sensors

What is piezoelectricity ?

Strain causes a redistribution of charges and results in a net electric dipole (a dipole is kind of a battery!)

A piezoelectric material produces voltage by distributing charge (under mechanical strain/stress)

Different transducer applications:Þ AccelerometerÞ Microphone

Piezoelectric Sensors

Above equations are valid when force is applied in the L,W or t directions respectively.

31 denotes the crystal axis

Piezoelectric Sensors - Circuitry

The Equivalent CircuitTaken from Webster, “Medical Instrumentation”

Voltage generartor

Capacitor to hold charge

Leakage Resistor

Temperature sensors

• Bimetallic strips• Resistance temperature detectors (RTD)• Thermistors• Thermodiodes and transistors• Thermocouples• Thermoelectric – Thermocouples• Radiation Thermometry• Fiber Optic Sensor

Temperature measurement with RTDTypical characteristics of RTD

Temperature measurement with RTD

For RTD made of platinum, the temperature profile is quite linear and can be represented by

20100

0

)()( TTTTRR

)( 000

TTRR

For RTD made of copper, the characteristics can be approximated by


ExampleA platinum RTD is connected as one arm of a Wheatstone bridge as shown

The fixed resistors, R2 and R3 are 25Ω. The RTD has a resistance of 25Ω at 0oC, and the coefficient of resistance of the RTD is

C/00395.0 o


2

31 RRRRRTD

A temperature measurement is made by placing a platinum RTD in the measuring environment and balancing the bridge by adjusting R1 to a new value of 37.36 Ω.Determine the temperature of the measuring environment

Solution

At balanced condition, we have

)1(2536.37 TFrom

We can find that the temperature is 126o C.

RTDs

RTDs are made of materials whose resistance changes in accordance with temperatureMetals such as platinum, nickel and copper are commonly used.They exhibit a positive temperature coefficient.

A commercial ThermoWorks RTD probe

Thermistors

Thermistors are made from semiconductor material.Generally, they have a negative temperature coefficient (NTC), that is NTC thermistors are most commonly used.

Ro is the resistance at a reference point (in the limit, absolute 0).

Over a small dynamic range a thermistor can be linearized

Temperature measurement with thermistors

The mathematical relationship describing a thermistor can often be expressed as

)/1/1(0

0TTeRR

As temperature increases, the resistance decreases.

R0 is the resistance at T0, and β is a parameter ranging from 3500 to 4600.


Example

A thermistor is placed in a 100oC environment, and its resistance is measured at 20,000Ω. The material constant, β, for this thermistor is 4000. If the thermistor is then used to measure a particular temperature, and its resistance is measured as 500 Ω, determine the environmental temperature being measured.


00

1)ln(11TR

RT

Solution:

From the basic equation of thermistor, we can have

C

TRRT 0

00

159.1101)ln(11

Further

Thermocouples

Seebeck EffectWhen a pair of dissimilar metals are joined at one end, and there is a temperature difference between the joined ends and the open ends, thermal emf is generated, which can be measured in the open ends.

This forms the basis of thermocouples.

In a bimetallic strip, each metal has a different thermal coefficient…this results in electromagnetic force/emf or bending of the metals.

Thermocouples: Example

Example

A type-J thermocouple circuit below is used to measure the temperature T1 . The thermocouple junction # 2 is maintained by 32o F. The voltage output is measured to be 15 mV.Determine the temperature T1.

Solution

The temperature T can be read off from the graph for type-J thermocouple to be 530o F.

Temperature measurement with thermocouplesStandard Thermocouple Compositions

Temperature measurement with thermocouples

10

Radiation ThermometryGoverned by Wien’s Displacement Law which says that at the peak of the emitted radiant flux per unit area per unit wavelength occurs when maxT=2.898x10-3 moK

Infrared or thermal cameras

Force sensors

• Load cell: cylindrical tubeto which strain gaugeshave been attached.• For forces up to 10MN• Also exist in the 0-5N upto the 0-50kN range(metal element for straingauges)• Nonlinear errors about +/-0.03% of full range,hysteresis error =/-0.02%,repeatability within +/-0.02% of full range

Light sensors

• • Photodiodes• • Phototransistors• • Photoresistors

Fluid sensors

• • Fluid Pressure:• – Piezoelectric sensors• – Tactile sensors• • Liquid Flow:• – Orifice plate• – Turbine meter• • Liquid level:• – Floats• – Differential pressure sensors

Liquid Flow Meter

• Mechanical – Displacement type (measuring Displacement)– Inferential type( measuring Velocity of flow)

• Magnetic Flow meter – Work on the principle of faraday effect

• Turbine Flow meterwork on the principle of turbine rotation

Magnetic Flow meter• E=C*B*L*V• E=Induced voltage• C=Dimensional

constants• B=Magentic flux• L=length of the

conductor(fluid) in meter

• V=velocity of the conductor(fluid) in meter

Accuracy=+ .5 to + 2%

Magnetic coil

Magnetic coil

pipe

V

L

B

Induced voltage E

Q=V*AQ=Volumetric flow rateV=fluid velocityA=cross sectional area of pipeQ=K*E, where K=A/(C*B*L)

Magnetic Flow meter• Advantages

– It can handle slurry and greasy materials– It can handle corrosive liquids– It has low pressure drop– Obstruction less– Available in large sizes and capacity(2.54 to 2540mm)– Capable of handling low flow and high flow– Bidirectional

• Disadvantages– Relatively expensive– Works with fluid having adequate conductivity– Relatively heavy due to coils– Pipe must be full at all times

Turbine Flow Meter• Q=T*F/K• K=Pulses /volume

unit(turbine constant)• T=Time constant in min• F=Frequency in Hz• Q=Volume Flow,

Gallon/min• Accuracy=+ .25 to +5%• Flow range=0.1 to 50,000

Gallon/min

Output VoltageMagnetic pickup

Flow

Turbine wheel

Turbine fins

Pipe

Turbine Flow Meter• Advantages• Good accuracy• Excellent repeatability• Fairly low pressure drop• Easy to install and maintain• Good Temperature and pressure rating• Can be compensated for viscosity• Disadvantage• High cost• Limited use in slurry• Problem caused by non lubricating fluids

Sensor selection

• Nature of the measurement required: variable to be measured, nominal value, range of values, accuracy required, required speed of measurement, reliability required, environmental conditions under which the measurement is being made.

• Nature of the output required from the sensor, which determines the signal conditioning requirements in order to give suitable output signals from the measurement.

• The possible sensors can be identified, taking into account such factors as range, accuracy, linearity, speed of response, reliability, maintainability, life, power supply requirements, ruggedness, availability, cost.

• Cannot be decoupled from signal conditioning

Bridge circuitsBridge circuit is used quite often to measure low level voltages, such as the outputs from RTD, thermister, or thermocouples.

In the case of a balanced bridge, there is no voltage drop between, B and C, hence, Ig = 0.

0RIRI 3311

0RIRI 4422

Bridge circuits (Cont)

Furthermore,

21 II and 43 II

Therefore, the following condition is established for a balanced bridge:

3

4

1

2

RR

RR

Any change in one arm of the bridge will destroy this balance condition. However, one can use the measured voltage across the bridge to calculate changes in one arm.


Suppose that a volt meter of infinite impedance (Ig = 0) is used to measure the voltage across points B and C. Because (Ig = 0),

The voltage drop will be:

33110 RIRIE

)RR

RRR

R(EE

43

3

21

1i0

21 II

Of course, under a balanced condition, 0E0


Under this condition, suppose that there is a change in R1, such that:

The corresponding change in voltage across B and C is

To simplify the analysis, if we assume that:

111' RRR

)RR

RRR

R(EE43

3

21'

1'

i0

RRRRR 4321


Then

Or

iE)R/R(24

)R/R(E

RE2E

E4Ri


ExampleAn RTD is connected in a Wheatstone bridge as shown:

Under a balanced condition, the parameters are given as follows:

100R1 500RR 32

The temperature constant of the RTD: C/00395.0 o


Questions:(a) What is the value of RRTD under the balanced condition ?

(b) As temperature changes, it is found that the maintain a new balance, the new value for R1 has to be:

95.103R1

Determine the change in temperature.

Solution: (a) Using the relation:

3

2

RTD

1

RR

RR

100RR 1RTD

early integrated circuits: analog ...

• Vo = - A V will saturate at power voltage unless V very

small• from which it follows algebraically that Vo = - (Rf /Ri) Vi

• (independent of A as long as A >> Rf /Ri)

Operational amplifier• operational amplifier input impedance is (Ri||Rf)

– okay for interfacing low impedance sources to analog-to-digital converters etc

– but not for small signals from high impedance sources– especially when high “common mode” signals are present

• e.g., the millivolt difference in two signals each near 10 volts

• “instrumentation amplifier” design gives each input its own amplifier, cross-references them to reduce common mode sensitivity, then differences them with an “ordinary” op amp

“Instrumentation amplifier”

A General Measurement System: An Instrument, for example

SensorSignal Conditioning

Processing / Display

Functional Block Diagram

Input Output

System

• Process• Machine• Experiment, etc.

Instrumentation

A General Measurement System: An Instrument, for example

SensorSignal Conditioning


Functional Block Diagram

Input Output

Control

System

What is data acquisition and data logging?

• Real Time Data Acquisition relates to data being acquired and used in the same time frame, such as when monitoring or controlling a system or process

• Data Logging is when acquired data is stored or logged for later use or analysis. Involves some form of memory.

What is data acquisition and data logging?

• Data acquisition and data logging is not a complex or mysterious science as viewed by some

• Data acquisition in its simplest form could be to measure the length of a piece of string with a ruler

• Data logging in its simplest form could be to write that measured length down on a sheet of paper

A data acquisition or data logging system

• A data acquisition or data logging system generally includes the following components:– sensors or transducers which provide the fundamental

information of the parameters to be measured– a device to convert the primary signal from the sensors into a

form compatible with information processing systems– a computer or other controller which supervises the overall

system, and manages the generated data

Plan your task• Before you start

– What am I trying to measure– How am I going to measure– How accurately do I want measure– How often do I need to measure

• During.– Calculations, Data reduction, Alarms

• After– How am I going to recover my data– What am I going to do with my data– Post processing

Parameters to measure

• There are many different parameters for which sensors or transducers are commonly available– temperature – pressure, force, mass, weight– velocity, acceleration, vibration– strain, stress, distortion, fatigue– flow, volume, level– length, width, depth, thickness, displacement– state, pulse, counter– composition, concentration

Types of sensors• Sensors produce an electrical output that is proportional to the

quantity of the parameter being sensed

• Electrical output from sensors can be– Voltage, direct or alternating– Current , current loop– Resistance, conductance– Frequency– Binary states or pulses (counts)– Serial data - RS232, RS422, RS485, SDI-12– Parallel data - BCD, Gray Code, quadrature encoded

Reading information from sensors

• Many sensors produce an analog signal, such as voltage, current, resistance, frequency, etc.

• Analog signals are measured by a process of analog to digital conversion or ADC

• Important characteristics of ADC are– accuracy– resolution– linearity– repeatability– speed– common mode range– electrical noise rejection

Number of channels• Most data acquisition systems have a single analog to digital

converter, and many input channels

• Input channels are selected for measurement by a switch or multiplexer (mux), which may be sequential or random. Switching may be by relay or solid state.

• Only one channel can be measured at a time

• Consideration must be given to ‘sensor bounce’ when a sensor is selected for measurement

Data recovery and transfer

• Data can be recovered from data acquisition systems and data loggers in various ways– Serial comms interface via direct connect, modem, cell

phone, radio, satellite– PCMCIA - modem, cell phone, LAN, memory card– Network port - Ethernet, field bus, proprietary, etc– Universal Serial Bus (USB)

• Data can be transferred and published using – Local Ethernet network– Intranet - email, web pages– Internet - email, world wide web pages

Data processing and reporting

• Collected data is analyzed and reported using any of– generic packages such as

• ASCII text editors• Spreadsheets• Databases

– general purpose data processing packages

– proprietary host software packages

Other functionality• In addition to the core functionality of data acquisition,

modern data acquisition and data logging systems have other functionality including– real-time calculations, statistics, FFT, etc– alarms testing for out of range conditions– control feedback to the measured system or process– a range of communications and memory options etc

Data acquisition outline General scheme of a data acquisition hardware (one

channel):

Current trends: multi-channel (simultaneous sampling), microprocessor- controlled

Special considerations: Correlate sampling type, sampling frequency (Nyquist

criterion), and sampling time with the dynamic content of the signal and the flow nature (laminar or turbulent)

Correlate the resolution for the A/D converters with the magnitude of the signal

Identify sources of errors for each step of signal conversion

Transducer (analog)

Signal Conditioning

- Offset, amplification,

filtering - (analog)

Storage (digital)

Sensor (analog)

A/D converter (digital)

http://www.clipart.com/en/close-up?o=1254813&memlevel=C&a=c&q=measurement%20systems&s=91&e=120&show=&c=&cid=&findincat=&g=&cc=&page=4

Data acquisition components Signal conditioning Analog multiplexers Converters Clock Master controller Digital input/output

device Input/output buffer Output devices

DA components

Signal conditioning: Output signal from transducers are conditioned prior to sampling and digital conversion. Analog multiplexer: Is a multiple port switch that permits multiple analog inputs to be connected to a common output. Converters: DAS uses an analog to digital converter to sample and convert the magnitude of the analog signal into binary numbers. Clock: Clock provides master timing for the DAS process by providing a precise stream of pulses to the various system components. Master controller: It provides the start and stop sequences for data acquisition to control actual flow into and out of the system. I/O device: Some transducers and measuring devices output a digital signal directly which, enables bypassing the A/D converter of the DAS. I/O buffer: This is a digital random access memory (RAM) where the data is stored before sending it to some other storage device. Output devices: Permanent storage or display devices (zip disk, hard disk, printer, etc.)

http://www.clipart.com/en/close-up?o=2670382&memlevel=C&a=c&q=information&s=91&e=120&show=&c=&cid=&findincat=&g=&cc=&page=4

http://www.clipart.com/en/close-up?o=650576&memlevel=C&a=c&q=boring&s=1&e=30&show=&c=&cid=&findincat=&g=&cc=&page=1

Signal typesSignal classification Analog

A signal that is continuous in time Discrete

Contains information about the signal only at discrete points in time

Assumptions are necessary about the behavior of the variable during times when it is not sampled

Sampling rate should be high so that the signal is assumed constant between the samples

Digital Useful when data acquisition and

processing are performed using a computer Digital signal exists at discrete values in

time Magnitude of digital signal is determined by

Quantization Quantization assigns a single number to

represent a range of magnitude of a continuous signal.

analog

discrete

digital

http://www.clipart.com/en/close-up?o=2972437&memlevel=C&a=c&q=analog%20signal&s=151&e=180&show=&c=&cid=&findincat=&g=&cc=&page=6

Preprocessing analog signals

• Filtering : eliminate aliasing, noise removal (filtering)– Low pass filter– High pass filter– Band pass filter– Notch filter

• Offset : offset voltage value subtracted from actual signal– Offset helps in assessing the intensity of fluctuation of a signal

• Amplification : signal level amplified to optimally suit the hardware it is fed into– Gain helps to amplify the signal– Generally the values are amplified to take full advantage of the range of A/D

converter.

Preprocessing deals with conditioning signals or optimizing signal levels to obtain desired accuracies.

AliasingConcept of sampling frequency : Digitization (conversion of

analog to digital signal expressed in the binary system) of analog signals is performed at equally spaced time intervals, t.

Of great importance is to determine the appropriate value of t (sampling data rate).

Accurate sampling of a fluctuating signal needs to be made with at least twice the maximum frequency in the flow (Nyquist criterion). Otherwise, aliasing occurs (confusion between low and high frequency signal components).

To eliminate aliasing, all the information in original data is removed above the Nyquist frequency (fA = 1/(2t)). Removal is achieved by using low-pass filtering that removes frequencies above fA before the data passes through the A/D conversion.

Effect of sampling rate

signal input channels• typical chain:

– transducer -> amplifier -> filter -> sample-and-hold -> ADC• high end device replicates this for each analog input• low end device multiplexes to save cost of downstream

components• typically the amplifier and filter (or “signal conditioner”) are

replicated per channel, then individual signals are selected in rotation and presented to the sample-and-hold and ADC

• caution 1: signals are sampled at different times:better to give each channel its own S/H, but it’s rarely done

caution 2: the manufacturer quotes the total ADC conversion rate, which may actually be shared by 16 or more channels!

Basic Stages of a Measuring System• Sensor/Transducer

– Sensor: Uses some natural phenomenon to sense the variable being measured

– Transducer: Converts the sensed information into a detectable signal

– Loading: The measured quantity is always disturbed • Signal Conditioning

– Modifies (amplify, filter) the signal for the final stage• Signal Processing

– Processes the signal to covert it so that other parameters can be measured (Fourier transform)

• OutputIndication or storing of the measured value

• Control/FeedbackUse of the signal to control its future value

– DMA, streaming to disk, etc• analysis

– tools for tabulation, arithmetic, transforms (FFT, etc), etc

• presentation– graphical representation of results in familiar

formats (even for particular journals)• dissemination

– integration with document preparation software– integration with web distribution and publication


Analog processing

Analog display (dial indicator, meter)

Digital display

Simple Alarm

Shut off the system/machine

Send it to another processing unit

Strip chart recorder

Any device that accepts analog input

A General Measurement System: An Instrument, for example – contd…


What is RS232?

• RS232 is a popular communications protocol for connecting modems and data acquisition devices to computers. RS232 devices can be plugged straight into the computer's serial port (also known as the COM or Comms port). Examples of data acquisition devices include GPS receivers, electronic balances, data loggers, temperature interfaces and other measurement instruments

The RS232 Standard• RS stands for Recommended Standard. In the

60's a standards committee now known as the Electronic Industries Association developed an interface to connect computer terminals to modems.

• Over the years this has been updated: the most commonly used version of the standard is RS232C (sometimes known as EIA232); the most recent is RS232E.

• The standard defines the electrical and mechanical characteristics of the connection - including the function of the signals and handshake pins, the voltage levels and maximum bit rate

The RS232 Standard

• If RS232 is a standard why can't I just use a standard lead to connect together two RS232 ports and expect them to talk to one another?

• The answer is that the RS232 standard was created for just one specific situation and the difficulties came when it is used for something else. The standard was defined to connect computers to modems. Any other use is outside of the standard. The authors of the standard had in mind the situation below:

The RS232 Standard

The RS232 Standard• The standard defines how computers ( it calls them Data

Terminal Equipment or DTEs) connect to modems ( it calls them Data Communication Equipment or DCEs).

• The standard says that computers should be fitted with a 25 way plug whilst modems should have a 25 way D socket. The interconnecting lead between a computer and a modem should be simply pin1—pin1, pin2—pin2, etc. The main signals and their direction of flow are described below.

• It is important to note that a signal which is an output from a computer is an input to a modem and vice versa. This means that you can never tell from the signal name alone whether it is an input or an output from a particular piece of equipment.

• Also, instead of being a DCE device, a data acquisition device might be configured as DTE. In this case you need an adaptor or the RS232 cable wired differently to normal. When the PC is connected to a DTE instrument, some of the cable wires must cross over.

The RS232 Standard

The RS232 Standard• Pin assignment• 1 Input DCD Data Carrier Detect • 2 Input RXD Received Data • 3 Output TXD Transmitted Data • 4 Output DTR Data Terminal Ready• 5 Signal Ground • 6 Input DSR Data Set Ready• 7 Output RTS Request To Send• 8 Input CTS Clear To Send • 9 Input RI Ring Indicator

Serial Hardware Connection

• RS-232– DCE or DTE

configurations– 9-pin or 25-pin

• RS-422– DCE or DTE– 8-pin

• RS-485– Multidrop

Pin DTE DCE

1 DCD Input Output2 RxD I O3 TxD O I4 DTR O I5 Com - -6 DSR I O7 RTS O I8 CTS I O9 RI I O

Serial Communication

Terminology• Baud rate – bits per second• Data bits – inverted logic and LSB first• Parity – optional error-checking bit• Stop bits – 1, 1.5, or 2 inverted bits at data end• Flow control – hardware and software handshaking

options

The RS232 Standard• TXD Transmitted Data, Pin 2 of 25 way D

This is the serial encoded data sent from a computer to a modem to be transmitted over the telephone line.

• RXD Received Data, Pin 3 of 25 way DThis is the serial encoded data received by a computer from a modem which has in turn received it over the telephone line.

• DSR Data Set Ready, Pin 6 of 25 way DThis should be set true by a modem whenever it is powered on. It can be read by the computer to determine that the modem is on line.

• DTR Data Terminal Ready, Pin 20 of 25 way DThis should be set true by a computer whenever it is powered on. It can be read by the modem to determine that the computer is on line.

• RTS Request to Send, Pin 4 of 25 way DThis is set true by a computer when it wishes to transmit data

The RS232 Standard• CTS Clear To Send, Pin 5 of 25 Way D

This is set true by a modem to allow the computer to transmit data. The standard envisaged that when a computer wished to transmit data it would set its RTS. The local modem would then arbitrate with the distant modem for use of the telephone line. If it succeeded it would set CTS and the computer would transmit data. The distant modem would use its CTS to prevent any transmission by the distant computer.

• DCD Data Carrier Detect, Pin 8 of 25 Way DThis is set true by a modem when it detects the data carrier signal on the telephone line..

• PC Serial PortsA nine pin D plug has become the standard fitting for the serial ports of PCs, although it's nothing to do with the RS232 standard. The pin connections used are

How Fast Can Instruments send data over RS232?

• The speed of RS232 communications is expressed in Baud. The unit is named after Jean Maurice-Emile Baudot (1845-1903), a French telegraph engineer and the inventor of the first teleprinter. It was proposed at the International Telegraph Conference of 1927

• The maximum speed, according to the standard, is 20,000 Baud. However, modern equipment can operate much faster than this.

• No matter how fast (or slow) your connection - the maximum number of readings per second you can take from your instrument depends on the software. For example, with Windmill software, speeds of up to 35 readings per second are achievable whilst with Streamer software this rises to 700 readings per second.

http://www.microlink.co.uk/windmill.html

http://www.microlink.co.uk/demo.html

How Fast Can Instruments send data over RS232?

• The length of the cable also plays a part in maximum speed.

• The longer the cable, the greater the cable's capacitance and the slower the speed at which you can obtain accurate results.

• A large capacitance means voltage changes on one signal wire may be transmitted to an adjacent signal wire.

• Fifty feet is commonly quoted as the maximum distance, but this is not specified in the standard.

• We generally recommend a maximum distance of 50 metres, but this depends on the type of hardware you are connecting and characteristics of the cable

RS-232 interfaces• before ethernet etc, we talked to timeshared

mainframes on RS-232• many instruments (oscilloscopes, lock-in amplifiers,

etc) are still sold with RS-232 set-up, control, and data download interfaces

• many devices (e.g., older PDAs) and peripherals (e.g., mouse, smart-card reader, X-10 controller, etc) still use it

• bytewise asynchronous: a start bit announces each incoming byte

• family of standards for single/dual symmetric/assymetric levels

• single device design; daisy chain with device identifier allows a loop of transducer interfaces (fragile!)

• serial nature makes interface to/from fiber optics easy

USB for Data Acquisition?

• The USB is extremely convenient for data acquisition for several reasons.

• The equipment can obtain power from the USB; it doesn't need to be battery powered or plugged into the wall. This makes USB ideal for portable data acquisition with a laptop.

• Using a USB hub you can connect many devices to one socket - letting you easily expand your system requirements grow.

• USB ports are provided on most new PCs - no need to open the computer and install adaptor cards.

• You can plug in and unplug your equipment without switching off your computer or even restarting Windows.

• The USB cable can be up to 5 m long. However, using USB hubs between cables you can reach 30m. Faster speeds than those allowed by RS232 connections are achievable

• You can use USB devices alongside existing data acquisition equipment (such as instruments that plug directly into the RS232 port).

IEEE 488 (GPIB, HPIB) interfaces• THE MAIN control and communication channel for

research-grade instruments in physical/chemical/etc sciences

• 16 bit parallel bus: 8 data or command lines, 8 control lines– control lines (8) = “data valid”, “not ready for data”, etc.

• a device may be a “talker” and/or “listener” and/or “controller”

• devices are uniquely addressed (0 ... 30 > 5 bits); 31 addresses all

• data sent one byte at a time, managed by the control lines

• high level generic instrument (voltmeter, oscilloscope, etc) control languages (e.g., SCPI = “skippy”) come and go; problem is that generic language cannot exploit unique features of any instrument

GPIB Hardware Specifications

1

12

13

24

DIO5DIO6DIO7DIO8RENGND (TW PAIR W/DAV)GND (TW PAIR W/NRFD)GND (TW PAIR W/NDAC)GND (TW PAIR W/IFC)GND (TW PAIR W/SRQ)GND (TW PAIR W/ATN)SIGNAL GROUND

DIO1DIO2DIO3DIO4EOIDAV

NRFDNDAC

IFCSRQATN

SHIELD

• Max cable length between devices = 4 m (2 m average)

• Max number of devices = 15

Emerging DAC communications

• Enhanced Parallel Port (EPP): bidirectionally, as needed for DAC

• Universal Serial Bus 2.0 (USB): hot insertion of up to 127 devices attractive for research environment; can power net devices; in practice, relatively slow (100 Kwords/s?)

• FireWire (IEEE 1394): fast enough for live video, can support 100s of devices

• 1451.2-1997 PDF Standard for a Smart Transducer Interface for Sensors and Actuators - Transducer to Microprocessor Communication Protocols and Transducer Electronic Data Sheet (TEDS) Formats 1998 ($101)

Industrial DAC• 4-20 mA Current loop: a medium rather than a

protocol, but you should know about it ... robust in noisy industrial environment

• MAP = Manufacturing Automation Protocol, driven by automobile manufacturers in 1980s; is it alive?

• DeviceNet: 125/250/500 Kbit/s, 8-bit data packet, suitable for high speed monitoring of simple process parameters, e.g., in discrete manufacturing of food containers, etc

• FieldBus: 1-2.5 Mbits/s, variable packet size to 1000-bytes, suitable for lower packet count of more detailed packets, e.g., in continuous process control of fast moving complex but relatively slowly changing data, e.g., as in oil refining

Research

MPS (Michigan Parallel Std., MSS University of Michigan

I2S Delf University of Technology

Time-Triggered Protocol University of Wien

Industrial

Hart Rosemont

DeviceNet Allen-Bradley

SP50 Fieldbus Fieldbus Foundation

LonTalk/Lonworks Echeleon Corp

Profibus DP/PA Siemens

ASI-Bus ASI

InterBus-S InterBus-S club, Phoenix

SERCOS VDW

IEEE-488 HP

ArcNet Datapoint

WorldFIP WorldFIP

Automotive

CAN Bosch

VAN ISO

D2B Philips

MI-Bus Motorola

J-1850, J 1939 (CAN),J2058, J2106

SAE, Chrysler, General Motors

Home automation

Smart House Smart House LP

CEBus EIA

I2C Philips

Building and Office Automation

BACnet Building Automation Industry

IBIbus Intelligent Building Institute

Batibus Merlin Gerin

EIbus Germany

Computer Hardware • Central Processing Unit - also called “The

Chip”, a CPU, a processor, or a microprocessor• Memory (RAM)• Storage Devices• Input Devices• Output Devices

Computer Hardware

• Central Processing Unit - also called “The Chip”, a CPU, a processor or a microprocessor

• Memory (RAM)• Storage Devices• Input Devices• Output Devices

http://images.google.com/imgres?imgurl=www.chips.ibm.com/products/memory/gfx/memory.jpg&imgrefurl=http://www.chips.ibm.com/products/memory/&h=150&w=148&prev=/images?q=memory&num=20&hl=en&sa=N

Computer Hardware • Central Processing Unit - also called “The Chip”, a CPU,

a processor or a microprocessor• Memory (RAM)• Storage Devices• Input Devices• Output Devices

http://asterix.ednet.lsu.edu/~stockard/socialstudies/2bbc8a70.jpg

Computer Hardware

• Central Processing Unit - also called “The Chip”, a CPU, a processor or a microprocessor

• Memory (RAM)• Storage Devices• Input Devices• Output Devices

CPU Types• CPU or microprocessor is often

described as the brain of a computer.• CPU is an integrated circuit or “chip” which

processes instructions and data.• CPU types.

– Intel Pentium II, III, IV– Intel Celeron– AMD Athlon

CPU types

• CPU speed is measured by the number of completed instruction cycles per second

Currently, CPU speeds range from 600 megahertz (MHz or million cycles per second) to 4 gigahertz (GHz or billion cycles per second).

• Always check new software’s requirements for CPU type and speed before purchasing

Microcomputer Platforms• All microcomputers are based on a small

number of designs (interior architecture) or computer platforms.

• PC architecture is based on the first IBM microcomputers. Generally, PCs use Microsoft Windows as their operating system.

• Apple computers or Macs are based on proprietary architecture manufactured exclusively by Apple Computer, Inc.

Microcomputer Platforms

• Compatibility refers to computers that operate in essentially the same way.

• Compatibility across platforms is limited! You must know which platform your computer runs on before purchasing software.

• All software is designed for a specific platform.

Windows, Mac or Unix versions

Memory (RAM)

RAM or Random Access Memory• “Waiting room” for computer’s CPU. • Holds instructions for processing data,

processed data, and raw data.• Ram is measured by:

– Capacity (in Megabytes or Gigabytes)– Speed (in Nanoseconds)

Memory (RAM)

• Amount of RAM installed will determine.–Which software applications will run (efficiently)?–How many software applications can be open

simultaneously (multitasking ability)?• RAM upgrades are cost-effective and

easy to install.Check your computer manual for RAM type (DIMM, SDRAM) and speed (100, 90ns).

Memory (RAM)

• All software applications will have RAM specifications listed on their packaging.

• Many applications list both a minimum and a recommended amount of RAM necessary to run the software.

• Be cautious about buying software for a system based on minimum requirement.

Visit the Memory Technology Exhibit

at Intel’s Virtual museum.

http://www.intel.com/intel/intelis/museum/Exhibits/hist_micro/hof/index.htm

http://www.intel.com/intel/intelis/museum/Exhibits/hist_micro/hof/index.htm

Storage Technology

• Electronic devices that store, retrieve, and save instructions and data.

• Today’s microcomputers or PCs include several types of storage devices.

• Capacity and speed are important considerations when selecting a new storage device for a PC.

http://images.google.com/imgres?imgurl=216.121.19.246/images/storage.jpg&imgrefurl=http://216.121.19.246/pages/storage.htm&h=258&w=508&prev=/images?q=storage+devices&num=20&hl=en&sa=G

Storage Technology• Magnetic storage devices

store data by magnetizing particles on a disk or tape. They have a limited life-span of 1 to 5 years, depending on the device.

• Optical storage devices store data as light and dark spots on the disk surface. They have an unlimited life-span.

http://images.google.com/imgres?imgurl=www.pns.anl.gov/ckl_science/Images%20folder/CD-ROM.gif&imgrefurl=http://www.pns.anl.gov/ckl_science/Materials/GaN_application.html&h=276&w=228&prev=/images?q=%22optical+storage+devices%22&num=20&hl=en

Storage Devices

Hard Disk Drives• Capacity is measured in gigabytes (GB or

billions of bytes).• Typically permanently installed.• Used to store operating system,

application software, utilities and data.• Magnetic storage device.

Learn more about how a hard disk drive works from How Stuff Works

website.

http://www.howstuffworks.com/hard-disk.htm

Storage DevicesFloppy Disk Drives• Capacity is 1.44 to 2.0

megabytes (MB or millions of bytes).

• Storage device with the smallest capacityMost portable storage media

Magnetic storage device.

Storage Devices

CD-ROM Drives• Typically installed on all new computer

systems. (Were add-on device until the mid 1990’s).

• Capacity is 600 to 750 megabytes (MB or millions of bytes).

• Most mass-produced commercial software is packaged on a CD.

Storage Devices

CD-ROM Drives• Used more often now for backup storage

as CD-RW (read/write) technology has become less expensive.

• Data is read from CD by a laser.• Optical storage device.

Learn how to write data, images, and audio to a CD from

Kodak’s website.

http://www.kodak.com/global/en/service/cdrMedia/index.jhtml

Storage Devices

Other Types of Drives• Zip Drives – Several different capacities are

available.• Tape Drives – Generally used for system

backups, becoming less common.• DVD drives – Can also read CDs, now more

common as a standard device on new computer systems.

Learn more about specific hardware components and their functions from

Tom’s Hardware.

http://www6.tomshardware.com/howto/20010115/pcsystem-14.html

Input Devices

• Input is all information put into a computer. Input can be supplied from a variety of sources:– A person– A storage device on computer – Another computer– A peripheral device– Another piece of equipment, such as a

musical instrument or thermometer

Input Devices

• Input devices gather and translate data into a form the computer understands.

• Primary input device:– Keyboard - Most common input device; used

to type in commands and data.– Mouse or trackball enhances user’s ability to

input commands, manipulate text, images.– Joystick useful in education as an adaptive

or assistive input device.

Input Devices

• Scanners are peripheral input devices which allow users to import:– Text– Graphics– Images

• Specialized software aids in translating information into a format the computer can understand and manipulate.

Input Devices

• Digital Cameras are peripheral input devices that allow users to create pictures and/or movies in a digital format.– Some require specialized

software to import images into the computer.

– Some record digital images directly to a disk that can be read by the computer.

http://images.google.com/imgres?imgurl=www.ginnphoto.on.ca/ginnphoto/images/digital-cameras-canon4.jpg&imgrefurl=http://www.ginnphoto.on.ca/ginnphoto/digital-cameras-canon.html&h=160&w=175&prev=/images?q=digital+cameras&num=20&hl=en

Output Devices

• Monitors are the most commonly used output device.

• Most monitors use a bitmap display. – Allows user to resize the display.– Divides the screen into a matrix of tiny square

“dots” called pixels.– The more “dots” a screen can display, the

higher the resolution of the monitor.

Output Devices

• Monitors are connected to a computer system via a port integrated on the video adapter or graphics card.

• Graphics cards convert digital data output from software to analog data for display on monitors.

Typically have additional memory chips on card, 4MB to 64MB.

Output Devices

Printers• Dot matrix

– Seldom used in a classroom.– Still frequently used in business.

• Bubble or ink jet• Laser

http://images.google.com/imgres?imgurl=www.bsos.umd.edu/oacs/equipment/printers.jpg&imgrefurl=http://www.bsos.umd.edu/oacs/graphicslab.html&h=150&w=165&prev=/images?q=printers&num=20&hl=en

Output Devices

Projection systems or classroom TVs can display information from a computer system on a larger screen for whole-class instruction.

View and excellent tutorial on hardware basics at Macromedia’s site.

Requires log-in and browser plug-in download.

http://www.trainingcafe.com/

http://images.google.com/imgres?imgurl=www.projectorspecs.com/img1.jpg&imgrefurl=http://www.projectorspecs.com/&h=219&w=321&prev=/images?q=projection+systems&num=20&hl=en

Connectivity• Wired Connectivity

• Ethernet, Fibre, etc.• Serial & Parallel• USB• Firewire• SCSI• DVI

• Wireless Connectivity• IrDA• GSM• Bluetooth• WiFi

Wired Connectivity• Cabling

– Ethernet already covered– Fibre connections offer higher capacity over

longer runs, e.g. 100Mbps over runs of 2000m, 1Gbps for FTTC or FTTH systems

– FDDI (Fiber Distributed Data Interface) is a high performance token ring LAN, but as it is more expensive and complex than fast Ethernet take-up is limited

– Fiber is more widely supported in cable TV, which also offers internet and telephony support

Serial & Parallel• Serial

– Traditional serial connection is through RS-232 and its successors

– Developed by Electronic Industries Association, so properly EIA-RS-232, subsumed by CCITT V.24

– Defines a physical layer protocol, incorporating mechanical, electrical, etc. interfaces

– Limited to 20kbps and 15m cable length (25 pin)– Newer standard is RS-422, up to 2Mbps over

60m, but requires 37 pin + 9 pin connectors

Serial & Parallel

• Parallel– Predominantly used for printer connection,

though some peripherals offer parallel port connectivity (e.g. ZIP drives, Backup tape, PDAs)

– Based on the principle of sending a byte of information at a time, by sending each of the 8 bits in parallel rather than the bit-stream model of the serial port.

– Offers a data rate of 0.8Mbps over 15m

USB

• Universal Serial Bus– Now released in version 2.0– Developed by a consortium including Microsoft

and Intel and offering, in version 1.0, transfer rates of around 12 Mbits/s

– Version 2.0 offers 360 - 480 Mbits/s – Uses a flat-head, 4 strip connector– Up to 127 peripherals can be daisy-chained– Supported by Intel, but not by NT

USB.3.0• Designed November 2008 Manufacturer USB

3.0 Promoter Group (Hewlett-Packard, Intel, Microsoft, NEC, ST-Ericsson, and Texas Instruments)Superseded by USB 3.1 (July 2013)

• General specifications: Width: 12 mm (A plug), 8 mm (B plug), 12.2 mm (Micro-A & Micro-B plugs) Height 4.5 mm (A plug), 10.44 mm (B plug), 1.8 mm (Micro-A & Micro-B plugs),

• Pins: 9• Electrical Max. current :900 mA• Bitrate :5 Gbit/s (625 MB/s)

https://en.wikipedia.org/wiki/Hewlett-Packard

https://en.wikipedia.org/wiki/Intel

https://en.wikipedia.org/wiki/Microsoft

https://en.wikipedia.org/wiki/NEC

https://en.wikipedia.org/wiki/ST-Ericsson

https://en.wikipedia.org/wiki/Texas_Instruments

https://en.wikipedia.org/wiki/USB_3.1

Firewire

• IEEE-1394– High-speed serial bus, originally called Firewire,

developed by Apple– Offers data rates of 100 - 400 Mbps– Now predominantly supported by Texas

Instruments and other third party developers, being overtaken by USB.

– Widely used for digital video– Offers limited daisy-chaining

IEEE 1394(S1600 and S3200 )• FireWire S1600 and S3200 using the modes

that, for the most part, had already been defined in 1394b and were further clarified in IEEE Std. 1394-2008. The 1.572864 Gbit/s and 3.145728 Gbit/s devices use the same 9-conductor beta connectors as the existing FireWire 800 and are fully compatible with existing S400 and S800 devices. It competes with USB 3.0.

• Steve Jobs declared FireWire dead in 2008.As of 2012, there were few S1600 devices released, with a Sony camera being the only notable use

https://en.wikipedia.org/wiki/USB_3.0

https://en.wikipedia.org/wiki/Steve_Jobs

SCSI

• Small Computer Systems Interface– Developed in the late 70s by Shugat

Associates as Sasi– Daisy-chained peripheral connection– Offered in a variety of flavours, SCSI-1, SCSI-

2, Fast-Wide SCSI, Ultra SCSI, Wide Ultra SCSI, Ultra 2 SCSI, Wide Ultra 2 SCSI, Ultra 3 SCSI & Wide Ultra 3 SCSI

– Offers data rates from 40 - 1280 Mbps

Wireless Connectivity

• IrDA– The Infra-Red Data Association was set up to

establish an open standard for short-range digital data communication between computers and peripherals

– Provides a wireless link capable of high-speed data transmission

– Needs clear line-of-sight and has limited range

– Uses the PCs Uart chip to provide a data rate of 112Kbps over a range of 1m

GSM

• Global System for Mobile Communications– Based on microwave technology, basic GSM

chips offer a transfer rate of 9.6 Kbps - 14.4 Kbps over a significant range

– GSM receiver/transmitter networks enable world-wide communications capability

– Take-up to date has predominantly been for voice telephony, though email links to SMS are beginning to prove popular

GSM (cont.)– Phase II GSM has introduced the high-speed,

circuit-switched data device (HSCSD) which is offering 28.8Kbps in devices such as Nokia’s Communicator and now in a large number of mobile phones

– The goal of megabit and, potentially, gigabit communication rates are being addressed in Phase III GSM, which we’ll discuss as breaking technology.

Bluetooth– Bluetooth is an industry consortium

developing a RF based local “push” protocol and technology, offering high data rates over short distances, permitting equipment based comms.

– offers transfer rates of up to 1 Mbps over about 10 metres

– uses 2.4GHz bandwidth with spectrum frequency hopping

WiFi• IEEE 802.11b

– basis of “Wi-Fi” standard– uses same 2.4 GHz band as Bluetooth, but offers

11Mbps over 100 metres• IEEE 802.11a

– Offers transfer rates up to 54Mbps in the 5GHz band, but range is more limited, around 30 metres.

• IEEE 802.11g– Now shipping, offering up to 54 Mbps in the 2.4GHz

band, also with a range of around 100 metres.– Uses an enhanced spectrum frequency-hopping

approach to reduce interference.– Several of the major vendors are already offering

enhanced variants running at 100Mbps

A protocol defines the following:• Network topology: star, ring, or bus (tree), etc.• ISO reference model layers: physical, datalink, network, transport,

session, presentation and application.• Data communication modes: simplex, half-duplex, or duplex.• Signal types: digital or analogue.• Data transmission modes: synchronous or asynchronous, etc.• Data rate supported: several bps (bits per second) to several Gbps.• Transmission medium supported: twisted, coaxial, optical or microwave.• Medium access control methods: CSMA/CD, or control token, etc.• Data format: transmission modes and individual protocol specifications.• Type, order of messages that are to be exchanged.• Error detection methods: parity, block sum check, or CRC.• Error control methods: echo checking, ARQ (Automatic repeat request)• Flow control methods: X-ON/X-OFF, window mechanisms, or sequence

Analogue-to-Digital Converters

• When data acquisition hardware receives an analogue signal it converts it to a voltage. It then digitises it with an analogue-to-digital converter, ready for transfer to a computer. This page discusses different types of A-D converters and explains the meaning of A-D hardware specification terms

http://www.microlink.co.uk/a-d.html



Types of Analogue-to-Digital Converters

• Generally 5 types of A-D converter are used: successive approximation, dual slope integrating, charge balancing, flash and sigma-delta converter






Analog-to-digital conversion (ADC)• “counter” or “tracking” ADC

– count number of steps needed to charge capacitor to same voltage as signal (only need comparitor, not measurer)

– simple, inexpensive, conversion time depends on signal amplitude

• successive-approximation ADC– controller (maybe computer) applies successive

approximations to a DAC and compares its output to the signal

– slow– output naturally serialized

• dual-slope integrating ADC– integrator “charged” by signal for fixed time, “discharged” by

fixed current for measure time– usually charge for fixed number of powerline cycles (reject

60 Hz)– slow but good noise immunity

• voltage-to-frequency ADC– count output of VFC for measured time– slow but good noise immunity

• flash ADC (common in frame grabbers)– resistor ladder divides reference voltage

into 2n steps– 2n-1 comparitors are “on” below the signal

voltage, off above it– one step to resolve, one step 2n > n

conversion: FAST!– but cost ~2n vs. something like n for other

methods

Analog to digital converter (ADC) Example

Successive Approximation Converter

• A successive approximation converter provides a fast conversion of a momentary value of the input signal.

• It works by first comparing the input with a voltage which is half the input range.

• If the input is over this level it compares it with three-quarters of the range, and so on.

• Twelve such steps gives 12-bit resolution. While these comparisons are taking place the signal is frozen in a sample and hold circuit.

• After A-D conversion the resulting bytes are placed into either a pipeline or buffer store. A pipeline store enables the A-D converter to do another conversion while the previous data is transferred to the computer.

• Buffered A-D converters place the data into a queue held in buffer memory. The computer can read the converted value immediately, or can allow values to accumulate in the buffer and read them when it is convenient.

• This frees the computer from having to deal with the samples in real time, allowing them to be processed in convenient batches without losing any data

http://www.microlink.co.uk/range.html

Analog to digital converter (ADC)

Successive approximation ADC


Example

For a 4-bit ADC converter as shown below, go through the conversion process when a voltage of 10.1 V is being converted to digital representation with the full scale analog voltage of 15 V.

Solution

The step size of this 4-bit converter is

0.9375215Q 4 V

The quantization error is

46875.022115E 4

q

Analog to Digital Conversion:Successive Approximation

• Most common form of ADC• Bits are calculated one at a

time and operation can be stopped at any point

• Each bit is found by comparing the input value to the value represented by all the bits calculated so far– Requires a DAC


MSB: Most Significant BitLSB: Least Significant Bit

For 1011, the error is: 2125.01.103125.10error

For 1010, the error is: 725.01.10375.9error

Analog to Digital Conversion:Flash

• Simplest, fastest form of ADC– Sometimes known as a

parallel converter• Voltage ladder divides

reference voltage into 2N steps, which are compared to the input voltage– Requires 2N resistors and

comparators– Limited by resistor accuracy

Flash Converter

• A flash converter is the fastest type of converter we use.

• Like the successive approximation converter it works by comparing the input signal to a reference voltage, but a flash converter has as many comparators as there are steps in the comparison.

• An 8-bit converter, therefore, has 2 to the power 8, or 256, comparators

Dual Slope Integrating Converter

This converter reduces noise but is slower than the successive approximation type.

It lets the input signal charge a capacitor for a fixed period and then measures the time for the capacitor to fully discharge at a fixed rate.

This time is a measure of the integrated input voltage, which reduces the effects of noise.

http://www.microlink.co.uk/noise.html

Specifications of Analogue-to-Digital Converters

• Many types of specifications for A-D converters are quoted by hardware manufacturers. Here we try to explain what some of them mean in practice, namely resolution, linearity, offset errors, sample and hold acquisition time, throughput, integration time and re-calibration.








Resolution

• The resolution of the A-D converter is the number of steps the input range is divided into.

• The resolution is usually expressed as bits (n) and the number of steps is 2 to the power n.

• A converter with 12-bit resolution, for instance, divides the range into 212, or 4096, steps. In this case a 0-10 V range will be resolved to 0.25 mV, and a 0-100 mV range will be resolved to 0.0025 mV.

• Although the resolution will be increased when the input range is narrowed, there is no point in trying to resolve signals below the noise level of the system: all you will get is unstable readings.

http://www.microlink.co.uk/range.html

http://www.microlink.co.uk/noise.html

Linearity

• Ideally an A-D converter with n-bit resolution will convert the input range into (2 to the power n)-1 equal steps (4095 steps in the case of a 12-bit converter).

• In practice the steps are not exactly equal, which leads to non-linearity in a plot of A-D output against input voltage.

Sample and Hold Acquisition Time

• A sample and hold circuit freezes the analogue input voltage at the moment the sample is required. This voltage is held constant whilst the A-D converter digitizes it.

• The acquisition time is the time between releasing the hold state and the output of the sample circuit settling to the new input voltage value. Sample and hold circuits are not used with integrating converters.

Throughput

• The throughput is the maximum rate at which the A-D converter can output data values. In general it will be the inverse of the (conversion time + the acquisition time) of the A-D converter.

• Thus a converter that takes 10 microseconds to acquire and convert will be able to generate about 100 000 samples per second.

• Throughput can be increased by using a pipelined A-D converter, so a second conversion can start while the first is still in progress. Throughput may be slowed down, however, by other factors which prevent data transfer at the full rate.

Integration Time

• An integrating A-D converter measures the input voltage by allowing it to charge a capacitor for a defined period.

• The integration averages the input signal over the integration time, which if chosen appropriately will average over a complete mains cycle thereby helping to reduce mains frequency interference.

• The throughput of an integrating converter is not the inverse of the integration time, as throughput also depends on the maximum discharge time

Re-Calibration• Some A-D converters are able to re-calibrate themselves

periodically by measuring a reference voltage, and compensating for offset and gain drifts. This is useful for long term monitoring since drifts do not accumulate.

• If the re-calibrations are set too far apart there may appear to be small discontinuities in the recorded data as the re-calibrations occur. (If you have a reading other than zero for a zero condition, then you have an offset error: every reading will be inaccurate by this amount.

• When the A-D converter is preceded by signal conditioning circuits offset errors need not normally be considered. Drift occurs because components in the amplifier change over time and with temperature. Drift is usually only significant for people trying to measure low-level signals - a few millivolts - over long periods of time or in difficult environmental conditions.)

Digital to analog converter (DAC)

DAC is a device which converts a digital value to analog one. The general circuit is shown below

Digital to analog converter (DAC)

)2a.....2a2a2a(VV nn

33

22

11Ro

Suppose a n-bit digital value is represented as

]a...aaa[ n321

Its corresponding analog value can be calculated as

where ia can be either 1 or 0.

Microcontrollers: Overview

• A microcontroller (uC) is a small, lightweight CPU which is usually combined with on-board memory and peripherals– Compact and low power (relatively)

• They are often used as a simple hardware to software interface as well as for in-situ processing– Often used as an analog to digital gateway– Allows for real-time feedback based on data

Microcontrollers: Features (1)

• Processor speed: Fundamental measure of processing rate of device– Value of interest is in MIPS, not MHz

• Supply voltage/current: Measure of the amount of power required to run the device– Multiple modes (sleep, idle, etc)

• It is possible to adjust the voltage and frequency of some devices in real time, thereby trading off speed and power usage

Microcontrollers:Features (2)

• Internal memory: Sometimes divided between program and data memory, the amount of information that can be stored on board– Can sometimes be supplemented by external

memory• I/O Pins: Individual points for communication

between the uC and the rest of the world– Can be digital or analog, general or special

purpose• Interrupts: Non-linear program flow based on

event triggers from peripheral or pins

Microcontrollers: Peripherals (1)

• Timers: Internal registers (any size) in the uC that increment at the clock rate – May have prescaler– May be combined with range testing for

interrupt– Watchdog timers reset processor if it hangs.

• Comparators: Input that effectively functions as a 1-bit ADC with a variable threshold set by an internal register– Often used for real-time data monitoring

Microcontrollers: Peripherals (2)

• ADC: Most ADCs used in sensor data collection are integrated with uC and are controlled via special registers– Watch for number of channels vs number of

inputs– Sampling speed will not take input switch into

account– Clock internally via timers (benefits?)– Very fast ADCs often combined with DMA

• DAC: Digital to analog converters are also include in some data collection driven uC– Mostly used for feedback and control

Microcontrollers:Communication (1)

• UART: Basic hardware module which mediates serial communication (RS232) – Simplest form of communication between uC and computer, but

limited by speed– Most modules are full duplex, but need to watch out for data

registers and flags• USB: High Bandwidth Serial Communication between uC

and a computer or an embedded host– Usually requires chips with specialized hardware and firmware– Requires custom driver on the host side or conforming to a

standard device class• SPI: Full duplex master-slave 4-wire protocol for data

transfer between uCs– Mbit transfer rates– Somewhat quirky protocol – Unlimted (almost) nodes, can change master

Microcontrollers:Communication (2)

• I2C: Half duplex master-slave 2-wire protocol for data transfer between uCs– kbit transfer rates– Tx/Rx based on slave addressing– Can invert protocol with sensors as masters

• RF: Radio frequency (>100 MHz) EM transmission of data– Built in to some newer special-purpose uC– Wireless spherical transmission– Much (much) more later

Microcontrollers:Silicon Labs

• 8051 derivate uC with high reconfigurability– Many programming environments available– Vary from 3mm2 to 100 pin packages

• General specs– Medium power– Max 100 MHz / 100 MIPS– Max 128K program space / 8K RAM– Max 16 bit ADC– UART/USB/SPI/CAN/PWM/Comparators

• http://www.silabs.com/products/microcontroller/

http://www.silabs.com/products/microcontroller/

http://www.silabs.com/products/microcontroller/

Microcontrollers: TI MSP430

• Proprietary TI low-power low-cost RISC chips– Highly supported by TI with great program

chain– Designed for intermittent sampling and fast

startup• General specs

– Very low power (flexible)– Max 32KHz / 8 MIPS– Max 50K program space / 10K RAM– Max 16 bit ADC– UART/SPI/DAC/LCD/PWM/Comparators

• http://www.ti.com/

http://www.ti.com/

Microcontrollers:Atmel AVR

• 8-bit RISC series of microcontroller chips– Large range of available devices covering many

interfaces, speeds, memory sizes, and package sizes– Large hobbyist development community with many

available toolchains and sample applications• General specs

– One MIPS per MHz– Models available up to 20MHz– Max 128K program space / 8K RAM– ADC/LCD Driver/Motor Control– UART/CAN/USB/IIC/SPI/DAC/LCD/PWM/

Comparators• http://www.atmel.com/

http://www.atmel.com/

Microcontrollers:Atmel ARM7 (AT91SAM7S series)

• 32-bit ARM microcontroller– Low power (for 32-bit machines)– Can run in 16-bit mode if needed

• General specs– Lots of memory (8-64KB RAM, 32-256KB

flash)– Variable speed up to 55MHz– Packed with peripherals (USB, ADC, SPI,

etc.)– Comes in LQFP 48 and 64 packages– Not suitable for beginners

• http://www.at91.com/

http://www.at91.com/

Classic Control Theory

Controller

System

Desired Value, vd

System Changes, sc

(Unknown and Known) Disturbances

Observed Value, vo

Temperature Control

The Control System sets the current supplied to the heating elements in the furnace to keep the

material temperature at the desired value.

Desired Temperature

Control System

Furnace and

Material

Temperature Sensor

P,I,D Control Law

• The control signal has 3 components:– Proportional Mode

• c(t) = KC e(t) + cb

– Integral Mode – Compensates error buildup over time• c(t) = (KC/I) e(t) dt + cb

– Derivative Mode – Attempts to match rate change• c(t) = KC D d/dt ( e(t) ) + cb

Display Technologies• The Technologies

– CRT– LCD

• Dual Scan• Active Matrix

– PDP• ALiS• PALCD

– ThinCRT– LEP

ATTRIBUTES

HIGH RESOLUTIONHIGH BRIGHTNESSLARGE VIEWING ANGLEHIGH WRITING SPEEDSLARGE COLOUR GAMUTHIGH CONTRASTLESS WEIGHT AND SIZELOW POWER CONSUMPTIONLOW COST

TECHNOLOGIES

• CATHODE RAY TUBE (CRT)• VACUUM FLOURECENT DISPLAY (VFD)• FIELD EMISSION DISPLAY (FED)• LIQUID CRYSTAL DISPLAY (LCD)• PLASMA DISPLAY PANEL (PDP)• ELECTROLUMINISCENT DISPLAY (EL)• ORGANIC LIGHT EMITTING DIODE (OLED)

CRT (Cathode Ray Tube)

• 100 year old technology– A glass bell envelope contains a vacuum and

an electron gun. By the application of a current, and electron stream is created, which is fired through the vacuum towards the inside face of the glass envelope. Here it strikes a phosphor layer, which converts the beam into visible light, colour being achieved through mixing varying levels of light intensity from red, green and blue phosphors.

CRT (Cathode Ray Tube) [cont.]

– As there’s only one electron gun, and one beam for each colour, the screen needs to be refreshed constantly. This is achieved by altering the angle of the beam with a magnetic deflector coil, which deflects the beam across each part of the screen from top left to bottom right in a movement known as a raster. If refresh rate is set at 75Hz and resolution is 1024x768 (XGA), this equates to painting 58,982,400 pixels per second.

CRT (Cathode Ray Tube) [cont.]

• Advantages of CRT– robust, well-known technology– high-quality resolution and image control

• Disadvantages of CRT– size (footprint) on monitors

• short or mini-neck tubes possible, but exacerbates distortion problems

– analogue technology

LCD (Liquid Crystal Display)

• Work by polarisation of light– Liquid crystals don’t emit their own light, but

depend on a cold cathode backlight being passed through a sandwich of glass, liquid crystal and polarising filters, at right angles to each other.

– The liquid crystal molecules need to be aligned to allow the light to refract along the chain and out the other side. By anchoring the long crystal molecules to each side of the screen by grooves in the glass, their natural state creates the necessary alignment.

LCD (Liquid Crystal Display) [cont.]

– When a current is applied to any screen element, the molecules lose the necessary alignment, so any light is blocked by the opposing polariser.

– Colour is produced in similar way to CRTs, with individual liquid crystal cells for red, green and Blue. Unlike phosphors, which emit light, the liquid crystals filter the light, allowing only their corresponding colours through.

CRT

100 YEAR OLD WORKHORSECATHODOLUMINISCENTBEAM SCAN DEVICELARGE VIEWING ANGLEHIGH BRIGHTNESSHIGH RESOLUTIONGOOD COLOUR GAMUTBEST PERFORMANCE TO COSTBULKY HEAVYUNIMPLEMENTABLE IN LARGE SIZESOBSOLESCENCESTILL ENJOYS 70% MARKET

VFD

• Earliest Flat technology• Low Cost• Good Luminance• Excellent Viewing Angle• Long Life• Matrix Addressing• Wire Emitters• Cathodoluminescent• Mechanical Complexity• Low Resolution• High Filament Power

EL

• The structure consists of two thin layers of dielectric with phosphor sandwitched between them. A thin Al layer on the top and thin ITO layer on the bottom completes EL.When voltage of order of 200V is applied the resultant high electric field (1MV/cm) tunnels electrons through dielectric on to phosphor. The high energy of electrons impact the colour centres to emit visible light.

• High brightness, high resolution,• Blue phosphor improvement required• High voltage switching• High purity materials• Small sizes• Expensive

LCD

• Most mature flat panel technology

• Major share of FPD market• Poor intrinsic viewing angle• Requires backlight• Inefficient• Slow• Effected by Temperature and

sunlight

PDP

• Large Displays >32”• High Resolution• High Brightness• Good Contrast• Good Colour gamut• Large viewing angle• High Speed• Presently High Cost

PDP Working

Address electrode causes gas to change to plasma state.

The plasma emits UV in discharge region which impinges on the phosphor

Reaction causes each subpixel to produce red, green, and blue light.

OLED

• Most promising technology

• Already in small sizes• No inherent size limit• Conformal displays• Large viewing angle• High resolution• High Speed• Good colour gamut• Lifetime issues to be

solved• Great threat to LCD 2008?

OLED advantages

• Colour Gamut comparable to CRT, with potential to get better – Striking visual appeal

• Thinner – No backlight• Less Expensive than LCD due to lesser

components– White + Color Filter route takes away some of

this advantage• Potential for printing in manufacturing.• Flexible and Conformal Displays

• The DMD is an array of several lakhs of aluminium mirrors, each of which acts as a light switch.

• It is a MEMS device.

Digital Mirror Device

Each mirror can rotate in one of two directions: + 10 degrees or -10 degrees.

+10 degrees is ON state. -10 degrees is OFF state.

FIGURE 8-22 continued Construction of an electrostatic-deflection CRT: (a) cutaway view; (b) electron beam detail.

Dale R. PatrickElectricity and Electronics: A Survey, 5e

Copyright ©2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.

FIGURE 8-23 Block diagram of a general-purpose oscillo-scope.




FIGURE 8-25 Digital storage oscilloscope. (Courtesy of Leader Instrument Corp.)




FIGURE 8-26 Block diagram of a typical digital storage oscilloscope (DSO).




Basic Operating Principles

• • Analogue device displaying graphs of voltage against• time• • Consists of: -cathode ray tube (CRT)• -amplifiers• -conditioning circuits• • General purpose scopes: 100Hz – 500KHz• one signal• • Sophisticated scopes: up to 100MHz• four different signals• • The electrical signals are observed with means of a• cathode ray tube

Basic Operating Principles

• • To observe a time-varying signal, the electron beam is• deflected in x-direction with means of a time base• generator which provides an output voltage in the form• of a saw-tooth• • To generate a stable image the triggering instant of• the saw-tooth has to be synchronized with the vertical• plate input• • In general, the way electrical quantities change with• respect to time, curve shapes of these changes and• other dependencies can be shown by a scope• • Oscilloscopes can be used for measuring electrical and• non-electrical variables• • For measuring the last mentioned one need converters,• sensors and transducers

Storage Oscilloscope

• • Ambiguous meaning; even digital oscilloscopes can• storage data, they are not generally referred as those• • The CRT scopes which are able to store data are called• “storage oscilloscopes”• • Used to examine non-repetitive transient signals• • Used to examine low frequency signals with much less• than 10Hz• • The highest frequency is about 0.1 MHz because of the• limited ability of screen to store information

Sampling Oscilloscope

• • Principle to reduce frequency limit of oscilloscopes• in case of repetitive waveforms• • Using the principle of equivalent sampling

Sampling Oscilloscope

• • Displayed sequentially samples show the shape of• original signal• • Frequency limit of sampling oscilloscopes is 10-50 GHz• • Disadvantage of noise sensitivity since signal• consists of samples of different signal periods• • Random sampling can also be used as principle for• sampling oscilloscopes, here samples of both, the• signal and the time base are taken randomly of

Lock-in Amplifier

• Introduction• A lock-in amplifier uses phase-sensitive detection to

improve the signal-to-noise ratio in cw experiments. Using phase-sensitive detection requires that the analytical signal be modulated at some reference frequency. The lock-in-amplifier then amplifies only the component of the input signal at the reference signal, and filters out all other frequencies, i.e., noise. In the fluorescence detection example illustrated below, the analytical signal (the fluorescence) is modulated by chopping the optical excitation source (the laser) at the reference frequency.

http://www.chem.vt.edu/chem-ed/spec/emission.html

http://www.chem.vt.edu/chem-ed/optics/sources/lasers.html

Frequency measurements• Two approaches: using frequency counter to measure

frequency directly, and using probe to measure the wavelength in a transmission line.

• Frequency counter approach

• (1) Basic principle: direct counting <500MHz• (2) Using frequency down-conversion techniques for

microwave signals• Pre-scaling: divider circuit <2GHz

Wavelength measurement approach

Microwave analyzers• Spectrum analyzer• Purpose: measure microwave signal spectrum, can also be used to measure

frequency, rms voltage, power, distortion, noise power, amplitude modulation, frequency modulation, spectral purity,...

• Operating principle

Audio Spectrum Analyzer Advantages

Specification definitions

Specifications and constrains

Operation principles

Project plan

Specifications Definitions:• Octave: two frequencies where one of the frequencies is two

times the frequency of the other.

• Signal to noise ratio (S/N ): the ratio of power of a desired signal at any point to the noise power at the same point.

• Distortion: signal distortion < 1% in 2nd harmonic

• Total harmonic distortion (THD): the ratio of the sum of the powers of all overtones to the power of the fundamental frequency.

• Dynamic range: the difference in decibels between the highest (overload level) and lowest (minimum acceptable) level of the input signal.

Acoustics & Vibration Research Group

Vrije Universiteit Brussel

Frequency Spectrum or Overall Level



Parallel Filter Spectrum Analyzer



FFT Spectrum Analyzer

msc lnstruments 2015

Documents

precision standard deviation

estimating precision

cr gg value

measurementsgross errors

mean value of iron gg

measurementssystematic

actual value

minimizedsystematic