Measurment and Instrumentation

MEASUREMENTS AND INSTRUMENTATION

Prepared ByCHARLES S.

Course Synopsis

• This course introduces the principles of instrumentation and measurements. It explores the working principles of DC & AC meters, oscilloscope and signal generators as well as the operation and application of various sensors and transducers

SYLLABUS SYLLABUS SYLLABUS SYLLABUS

UNIT – I STANDARDS AND INDICATING INSTRUMENTS

• SI units – Units for charge, voltage, current, power, energy, flux. Standards – Brief Introduction.

• Deflecting, controlling and damping forces in indicating instruments –

• Moving iron : attraction and repulsion type instruments, errors.• Moving coil instruments – Permanent magnet moving coil

instruments, Dynamometer type moving coil Instruments, Torque equations, errors.

• Ballistic Galvanometer – extension of ranges, use of shunts and Instrument Transformers.

SYLLABUSSYLLABUSSYLLABUSSYLLABUS

UNIT - II MEASUREMENT OF POWER AND ENERGY

• Dynamometer type wattmeter – Torque expression, Errors. Energy meters, Calibration of energy meters.

• Measurement of power using Instrument Transformers.

• Maximum demand indicator, Trivector meter, Power factor meter

• Power Analyzer.


Unit III - BRIDGES

• Resistance measurement - Wheatstone bridge, Kelvin double bridge, substitution method. –Transformer ratio bridges – Measurement of Earth resistance.

• Measurement of inductance and capacitance –Maxwell’s Bridge, Anderson Bridge, DeSauty’sBridge and Schering bridge.


UNIT - IV TRANSDUCERS AND MEASUREMENTOF NON-ELECTRICAL QUANTITIES

• Transducers – Classifications, Principle of operation of Resistance potentiometer, LVDT, Strain Gauge and Piezo-electric transducers.

• Encoders. • Measurement of Pressure and Flow – Measurement of

Temperature: Resistance thermometers, thermistors, thermocouples, optical and Radiation pyrometers.


UNIT – V DIGITAL INSTRUMENTS

• Electronic voltmeter – Digital voltmeter of ramp and integrating types.

• Digital Multi meter – block diagram. • Block diagram of dual channel oscilloscope. • Spectrum Analyzer.• Signal and function generators. • Harmonic distortion analyzer. • Strip chart and X-Y recorders, Field Bus

Instrumentation.

Introduction to Instrumentation and

Measurements

Measurement?

• The Measurement of a given quantity is essentially an act (or) the result of comparison between the quantity and predefined standard. It expressed in numerical values

• Measurement is the process by which one can convert physical parameters to meaningful numbers

Measurement?

Simple instrument method

Measurement?

In order that the results of measurement are meaningful there are two basic requirements

• The standard used for comparison purposes must be accurately defined and should be commonly used

• The apparatus used and the method adopted must be provable

Methods of measurement

1. Direct method : The unknown quantity is directly compared against a standard . The result is expressed as a numerical value e.g.. Length , Mass , Time

2. Indirect method: Measurement of indirect methods are not always possible, feasible, and practicable. These methods in most of the cases are inaccurate because they involve human factors

Instrument and Measurement Systems

• Measurements involve the use of instrumentsas a physical means of determining quantities (or) Variables

• In simple cases, an instrument consists of a single unit which gives an output reading (or) signal according to the unknown variable applied to it.

• In more complex measurementsituations a measuring instruments may consists of several separate instruments. These elements may consists of transuducing elements which convert the measured to an analogues form.

Instrument and Measurement Systems

Process Instrumentation System

Classification of the instruments

They are many ways in which instruments can be Classified broadly

1. Absolute Instruments These instrument give the magnitude of the quantity under measurement in terms of physical constants of the instrument

2. Secondary InstrumentsThese instruments are so constructed that the quantity being measured can only be measured by observing the output indicated by the instrument

Measurement Standards

• Based on definition of the seven

fundamental SI units of measurement

• Categorized into four:– International standard (SI)– Primary standards– Secondary (transfer) standards– Working standards

Base Units of Measurement

Deflection type instrument

• The deflection of the instrument provides a basis for determining the quantity under measurement

• The measured quantity produces some physical effect with deflects (or) produces a mechanical displacement of the moving system of the instrument

• An opposing effect is built in the Instrument which tries to oppose the deflection (or) the mechanical displacement of the moving system

Deflection type instrument

• The opposing effect is closely related to the deflection

• The opposing effect is so designed that is magnitude increases with the increase of deflection

• The balanced is achieved when opposing effect equals to cause producing the deflection.

• The value of measured quantity can be measured from the deflection, at the point of balance

PMMC type Instrument

Spring

θ

Td

Tc

Td = G.I [ where G is depends Flux density, number of turns are the moving coil

Tc = K.θ [ where K is the spring constant which depends upon the material and dimensions of the spring

I

PMMC type Instrument

Advantages: 1. Uniform Scale 2. Since Driving power is small, Power Consumption is

Low 3. Due to aluminum or Copper former hysteresis loss is

absent 4. Using shunt or multipliers the ranges can be extended

Disadvantages: 1.Ac quantity cannot be measured 2. Compare than the PMMI, its costlier 3. Friction, Temperature, ageing of control springs might

introduce errors

• In this instrument, a zero (or) null indicationleads to determination of the magnitude of the measured quantity

• A null type instrument attempts to maintain the deflection at zero by suitable application of an effect opposing that generated by the measured quantity

Null type instrument

Null type instrument

Slide WireSliding Contact

DC Potentiometer

a b

Summarize the above two instruments

• Null Type instrument are more accurate than the deflection type instrument

• Null Type instrument is highly sensitive as compared with the deflection type instrument

• Deflection type instrument are more suited for measurements under dynamic conditions

Damping Systems

• Definition:The action of reducing the vibration of an object. This tends to return the vibrating object to its original position.

• The damping torque should be such of a magnitude that pointer quickly comes to its final steady position, without overshooting

1. Under damped 2. critical damped 3. Over damped

Damping Systems

• The Damping device should be such that it produces a damping only While the moving system is in the motion

• The effective damping torque should be proportional to the velocity of the moving system

Damping Systems

1. Under damped:The moving system will oscillate about the final steady state position with a decreasing amplitude and will take some time before it comes to rest.

2. Critical damped:When the moving system moves rapidly but smoothly to its final steady position, the instrument is said to critical damped

3. Over damped:If the damping torque is more than what is required for critical damping, the instrument is said to be over damped

Damping Systems

The methods of producing damping torque

1. Air friction damping

2. Eddy current damping

Air friction damping

When the piston moves in to chamber, the air inside is compressed and pressure of air thus build up, opposes the motion of piston

When the piston moves out of chamber , the pressure in closed space Falls, and the pressure on the open side is greater than the other side

Eddy current damping

In Fluid Friction damping oil is used in place of Air

� Viscosity of oil is greater

�The damping force is also correspondingly greater

�When the moving system moves, the disc moves in oil and a frictional drag is produced

�The Frictional drug always opposes the motion

Eddy Current damping

• When a conductor moves in a magnetic field an emf is inducedin it if a closed path is provided, then the current flows, this current known eddy current

• This current interact with the magnetic field to produce electromagnetic torque which opposes the motion

• This torque is proportional to the strength of the magnetic field and current product

T α ϕ α I• The current is proportional to emf which in turn is proportional

to velocity of the conductor

I α emf α velocity of the conductor

Electromagnetic Damping

• The movement of a coil in a magnetic field produces a current in the coil which interacts with the magnetic field to produce a torque

• This torque opposes the movement of the coil and slows the response

Moving Iron Instrument

• In moving iron are movable system consists of one (or) pieces of specially shaped soft iron

• Which are so pivoted (central point) as to be acted upon by the magnetic field produced by the current in the coil

1. Attraction type2. Repulsion type


• A plate or vane of high permeability steel forms the moving element of the system

• This iron van is so situated that it can be move in a magnetic field produced by the stationary coil

• The coil is excited by the current (or) voltage under measurement


• When the coil is excited, it becomes an electromagnet and the iron van moves in a such a way so as to increase the flux of the electromagnet

• This is because iron vane tries to occupy a position of minimum reluctance

• Thus the force produced is always in such a direction

1. Attraction type

2. Repulsion Type

Repulsion Type


Attraction Type Repulsion type

Permanent Magnet Moving Coil Instrument [PMMC]


The general theory of moving-coil instruments may be dealt with considering a rectangular coil of N turns, free to rotate about a vertical axis.


• A moving coil instrument consists basically of a permanent magnet to provide a magnetic field and a small lightweight coil is wound on a rectangular soft iron core that is free to rotate around its vertical axis

• When a current is passed through the coil windings, a torque is developed on the coil by the interaction of the magnetic field

• The aluminium pointer attached to rotating coil and the pointer moves around the calibrated scale indicates the deflection of the coil


• Principle of operation It has been mentioned that the interaction between the induced field and the field produced by the permanent magnet causes a deflecting torque, which results in rotation of the coil.

1.Deflecting Torque

2. Controlling Torque

3.Damping Torque


• Deflecting Torque

If the coil is carrying a current of .iamp ,

The force on a coil side = BilN (newton, N).

∴Torque due to both coil sides = (2r)BilN (Nm)= Gi (Nm)

Where, GI- is the Galvanometer constant and it is expressed as

G = 2rBlN (nm/amp)= NBA

(note A= 2rl -area of the coil.)


• Controlling Torque

The controlling torque is directly proportional tothe angle of deflection of the coil.

Control Torque = Kθ

Whereθ – Deflection angleK – Spring Constant Nm/rad


• Damping Torque: It is provided by the induced currents in a

metal former or core on which the coil is wound or in the circuit of the coil itself

As the coil moves in the field of the permanent magnet, eddy currents are set up in the metal former or core.

The pointer will therefore swing more slowly to its proper position and come to rest quickly with very little oscillation.

Types of strain gauges

• Unbonded metal strain gauge• Bonded metal wire strain gauge• Bonded metal foil strain gauge• Vacuum deposited thin metal film strain

gauges.• Sputter deposited thin metal film strain gauge.• Bonded semiconductor strain gauges.• Diffused metal strain gauge.

Unbonded metal strain gauge

• Used almost exclusively in transducer applications.

• At initial preload , the strains and resistances of the four arms are normally equal, with the result the output voltage of the bridge, e0=0.

• Application of pressure produces a small displacement , the displacement increases tension in 2 wires and decreasing the resistance of the remaining 2 wires.

• This causes an unbalance of the bridge producing an output voltage which is proportional to the input displacement and hence to the applied pressure.

Bonded metal wire strain gauge

• It consist of a grid of fine resistance wire of diameter of about 0.025mm.

• The wire is cemented to a base.

• The base – thin sheet of paper or bakelite.

• Wire is covered with a thin sheet of material so that it is not damaged mechanically.

• The spreading of wire permits a uniform distribution of stress over a grid.

Bonded metal foil strain gauge

�Extension of the bonded metal wire strain gauge.

�The bonded metal wire strain gauge have been completely superseded by bonded foil strain gauge.

�The local increase in area reduces the transverse sensitivity which is a spurious input since the gauge is designed to measure the strain component along the length of grid elements

Metal foil strain gauge

Semiconductor strain gauge.

The resistance of the semi conductors changes with change in applied strain

The semiconductor strain gauge depends for their action upon piezo resistive effect. (i.e. the change in the value of the resistance due to change in resistivity.)

Measurement of pressure and flow

• Measurement of flow – It mainly operate on the principle of placing

on obstruction in the path of fluid causing a change in fluid pressure which is dependent upon the rate of flow

– Thus by measuring the difference in pressure before and after the obstruction by means of a differential pressure sensors, the rate of flow may be determined

– The examples of these flow meters Orifice plate, Venturi tube, Rotameter

•The turbine flow meter (better described as an axial turbine) translates the mechanical action of the turbine rotating in the liquid flow around an axis into a user-readable rate of flow The turbine tends to have all the flow traveling around it.

•The output is usually in the form of a digital electrical signal whose frequency is directly proportional to flow rate and whose total count is proportional to the total quantity , as each pulse represents a discrete volume

Temperature measurement

• One of the most common devices for measuring temperature is theglass thermometer.

• This consists of a glass tube filled with mercury or some other liquid, which acts as the working fluid.

• Temperature increases cause the fluid to expand, so the temperature can be determined by measuring the volume of the fluid.

• Such thermometers are usually calibrated, so that one can read the temperature, simply by observing the level of the fluid in the thermometer.

• Another type of thermometer that is not really used much in practice, but is important from a theoretical standpoint is thegas thermometer.

Classifications

• Other important devices for measuring temperature include:

• Thermocouples• Thermistors• Resistance Temperature Detector (RTD)• Pyrometers• Langmuir probes (for electron temperature of

a plasma)• Infrared

Resistance Thermometers• The resistance of the conductor changes when

its temperature is changed. This property is utilized for measurement of temperature.

• The variation of resistance R with temperature T can be represented by the following relationship for most of the metals as

R=R0(1+α1T+ α2T2+…+ αnTn+………)• Where R0=resistance at temperature T=0

and • α1 ,α2,αn are constants.• The resistance thermometer uses the change in

electrical resistance of conductor to determine the temperature

• It’s a positive temperature coefficient.

R T

Requirements of a conductor material to be used in (Resistance

Temperature Detector) RTDs are

• The change in resistance of material per unit change in temperature should be as large as possible.

• The material should have a high value of resistivity so that minimum volume of material is used for the construction of RTD.

• The resistance of material should have a continuous and stable relationship with temperature.

• Contraction of a term “thermal resistors”

• Its composed of semiconductor materials.

• Used in applications which involve measurements in the range of -60oC to 15oC

• The resistance of thermistors ranges from 0.5ς to 0.75 Mς

Thermistors

Thermistors

Composed of sintered mixture of metallic oxides such as manganese, nickel , cobalt, copper, iron and uranium.

Typical resistance–temperature characteristics of thermistor materials.

Applications thermistors

1. Measurement of Temperature

2. Control of temperature

3. Temperature compensation

4. Measurement of power at high frequencies

5. Measurement of thermal conductivity

6. Measurement level, flow and pressure of liquids

Thermocouple

• When two metals having different work functions are placed together, a voltage is generated at the junction which is nearly proportional to the temperature. This junction is called a thermocouple.

• A thermocouple or thermocouple thermometer is a junction between two different metals that produces avoltagerelated to a temperature difference.

Construction of thermocouples

Measurement of Thermocouple output

• The output emf of a thermocouple as a result of difference between temperatures of measuring junction and reference junction can be measured by the following methods

1. Measuring the output voltage directly with PMMC

2. Measuring the output voltage with the help of DC potentiometer

3. Measuring the output voltage after amplifying it

Pyrometer

• It is a temperature-measuring device, originally an instrument that measures temperatures beyond the range of thermometers, but now in addition a device that measures thermal radiation in any temperature range

• A pyrometer is a non-contacting device that intercepts and measures thermal radiation, a process known as pyrometry. This device can be used to determine the temperature of an object's surface.

• These pyrometers find applications for temperatures which are above the range of thermocouples and also for rapidly moving objects

Optical Pyrometers

The Radiations from a heated body at high temperatures fall with in the visible region of the electromagnetic spectrum

For a given wavelength in the visible region the energy radiated is greater at high temperatures

Within the visible region a given wavelength has a fixed colour and the energy of radiation is interpreted as intensity or brightness

Therefore if we measure brightness of the light of a given colour emitted by a hot source , we can have an indication of temperature

Optical Pyrometers

• In an optical pyrometer the wavelength of radiation accepted is restricted by means of a colour filter and the brightness is measured by comparison with standard lamp.

• An image of the radiating source is produced by a lens and made to coincide with the filament of electric lamp.

• The current through filament is made variable so that lamp intensity can be adjusted.

• The current through filament is adjusted until the filament and the image are of equal brightness

Optical Pyrometers

• When the brightness of image produced by the source and brightness produced by the filament are equal, the outline of the filament disappears

• The range of temperature which can be measured in the order of 1400 0 C

• Applications1. Temperature of furnace2. Temperature of molten metals and other heated materials

Radiation Pyrometers

Radian pyrometry measures the radiant heat emitted or reflected by a Hot object

Thermal radiation is electromagnetic radiation emitted as a result of temperature

The radiation detector is either a thermal detector, which measures the temperature rise in a black body at the center point of the optical system


• Thermal detectors respond equally to all wavelengths in the frequency spectrum, and consist of either thermopiles, resistance thermometers or thermistors.

• All of these typically have time constants of several milliseconds, because of the time taken for the black body to heat up and the temperature sensor to respond to the temperature change.


• The operation of thermal radiation pyrometers is based upon blackbody concepts

• The total thermal radiation emitted by blackbody is:

•4 2

9 2

0

/

tan 57.2 10 /

bq T W m

where Boltzmann cons t W m

T absolutetemp

σσ −

=

= = ×=

UNIT V

Digital Instruments

Digital Voltmeter [DVM]

• A digital voltmeter displays the value of a.c or d.c voltage being measured directly as discrete numerals in the decimal number system

• Advantages:

• It eliminates the observational errors committed by operators

• Parallax and approximation are entirely eliminated • Increase the speed which readings can be taken • The output values we can store for future computations

by using memory devices

Digital Voltmeter

Types :

1. Ramp Type DVM

2. Integrating type DVM

3. Potentiometric DVM

4. Successive approximation type DVM

5. Continuous balance type DVM

1. Ramp type voltmeter

• The digital voltmeter is to measure the time that a linear ramp voltage takes to change from level of input voltage to zero voltage (vice versa)

• This time interval is measured with an electronic time interval counter and the count is displayed as a number of digits on electronic indicating tubes of the output readout of the voltmeter

Linear ramp type DVM

Ranging &

Attenuator

Ramp

Generator

Oscillator Gate CounterRead out

Sampled RateMV

Input Voltage

Input

ComparatorStart pulse

Ground

Comparator

Stop pulse

Integrating Type DVM ( Voltage to Frequency Conversion )

• A constant input voltage is integrated and the slope of the output ramp is proportional to the input voltage

• When the output voltage reaches a certain value, it is discharged to 0 and another cycle begins

• The frequency of the output waveform is proportional to the input voltage

Integrating Type DVM

Digital Frequency

Meter

Pulse Generator

e0

er

eiR1

R2

t1 t2Pulse

er Waveformsat output of the integrator

Output of the Pulse generator

Multimeter

• A multimeter or a multitester , also known as a volt/ohm meter or VOM, is an electronic measuring instrument that combines several measurement functions in one unit.

• A typical multimeter may include features such as the ability to measure voltage, current, resistance, etc……….

• There are two categories of multimeter,1. Analog multimeter and2. Digital multimeter

Digital Multimeter

• The current is converted to voltage by passing it through low shunt resistance.

• The a.c quantities are converted to d.c by employing various rectifier and filtering circuits

• While for the resistance measurements the meter consists of a precision low current source.

Digital Multimeter

signal generator

• signal generator is an electronic device that generates repeating or non-repeating electronic signals (in either the analog or digital domains).

• These instruments usually produce a fixed frequency sine wave, whose output can be frequency or amplitude modulated by another signal.

• The instruments cover a frequency range of 0.001Hz to 50GHZ

signal generator

Oscillator Amplitude

Modulation Circuit

Attenuator Output amplifier

Detector

Comparator FeedbackAmplifier

Input for Amplitude Modulation

Input for Frequency Modulation

Output

signal generator

• Frequency ModulationIt is achieved by varying the voltage across

a variable capacitance diode in the tuning circuit of the oscillator

This gives a system with low output distortion, for modulation depths below 1% of the carrier frequency

During the frequency modulation manual or automatic methods may be used to keep the amplitude of the output constant

signal generator

• Amplitude Modulation It is most conveniently done by varying the

supply voltage to the oscillator

• Feedback – can be used to reduce to reduced output distortion

• Output To obtain the modulation envelop,

comparing this with the amplitude modulation input, then amplifying and feed back the difference as the modulation signal

Function Generator

• It’s a Versatile instrument that delivers a choice of different waveforms whose frequencies are adjustable over a wide range

• The outputs are – Sine wave – Triangular Wave– Square Wave– Saw tooth Wave

Simple Oscillator Circuit

Threshold Decision Oscillator

Function generator

Function Generator

• Features – These various outputs of the generator are available

simultaneously

– Useful feature of the function generator is that it can be phase locked to an external source.

– One function generator can be phase locked with second function generator, the two output signals can be displaced in phase by an adjustable amount.

– The function generator can be phase locked to a standard frequency of the source.

– Output waveforms of the generator will have same accuracy and stability as that of standard source

STORAGE AND DISPLAY DEVICES

� Magnetic disk and tape� Recorders� digital plotters� Printers� CRT display� digital CRO� LED� LCD � Dot Matrix Display.

Recorders

� A recorders records electrical and non electrical quantities as a function of time.

� They are used for having permanent records. It monitors continuously the condition state or value of the process variable such as flow, force, pressure, temperature, current , voltage, electrical power etc.

� Current and voltage can be recorded directly while the non electrical quantities are recorded indirectly by first converting them to equivalent currents or voltages with the help of sensors or transducers.

Recording device

Analog recorders Digital recorders

Incremental digital Synchronous digitalOscillographic recorders Magnetic tape recorders

Graphic recorders

Strip Chart recorders

X-Y recorders

Circular Chart recorders

Galvanometer type

Null type

LVDT recorders

Potentiometric recorders Bridge recorders

Strip Chart

• Strip Chart Recorder are those in which data is recorded on a continuous roll of chart paper moving at a constant speed

• The recorder records the variation of one of more variables with respect to time

Strip Chart

• It consists of – A long roll of Graph paper moving vertically

– A system for driving the paper at some selected speed (1 – 100 mm/s)

– A stylus for making marks on the moving graph paper. The stylus moving horizontally in proportional to the quantity being measured

– A stylus driving system which moves the stylus in a nearly analog of the quantity being recorded

Strip Chart

Stylus

• Most recorders use a pointer attached to the stylus

• So that the instantaneous value of the quantity being recorded can be measured directly on the calibrated scale

Strip Chart

• Most strip chart recorders use a servo feedback system, to ensure that the displacement of the pen across the paper tracks the input voltage in the required frequency range

• A potentiometer system in generally used to measure the position of the writing head

• The Chart paper drive system generally consists of a stepping motor which controls the movement of the chart paper at a uniform rate.

Strip Chart

• Basically it having three types of mechanisms

– Paper Drive Systems– Marking mechanism – Tracing systems

Paper Drive Systems

The paper drive system should move the paper at a uniform speed

A spring wound mechanism may be used in most of the recorders a synchronous motor is used for making marks on the paper

Strip Chart

• Marking mechanism– There are many types of mechanisms used for

making marks on the paper

1. Marking with ink filled stylus

2. Marking with heated stylus3. Chopper Bar

4. Electric Stylus Marking

5. Electrostatic Stylus 6. Optical Marking method

Strip Chart

• Types of Strip Chart Recorders

– Galvanometer Type

– Null Type recorder

Galvanometer Type

Null Type recorder

Strip Chart

X-Y Recorders

Oscilloscope

• An oscilloscope(abbreviated sometimes asscopeor O-scope) is a type ofelectronic test instrumentthat allows signal voltages to be viewed, usually as a two-dimensional graph of one or more electricalpotential differences(vertical axis) plotted as a function of time or of some other voltage

• The CRO depends on the movement of an electron beam, which is bombarded on a screen coated with a florescent material, to produce a visible spot.

• If the electron beam is deflected on both the conventional axes (i.e X-axis and Y-axis)

Oscilloscope

• The Oscilloscope is basically an electron beam voltmeter.

• The heart of the oscilloscope is the Cathode Ray Tube (CRT) – Which makes the applied signal visible by the

deflection of a thin beam of electrons.

Cathode Ray tube

H.T. supply

heater supply

Vertical Deflection plates

+-phosphor screen

anode

HorizontalDeflection plates

Electron Gun

Cathode Ray tube

• The Electron gun assembly produced a sharply focused beam of electrons which are accelerated to high velocity

• The focused beam of electrons strikes the Fluorescent screen with sufficient energy to cause a luminous spot on the screen

• After leaving the electron gun, the electron beam passes through two Paris of “Electrostatic Deflection” plates

Cathode Ray tube

• Voltage applied to these plates deflect the beam

• Voltages applied to one pair of plates move the beam vertically up and down – and the voltage applied to the other pair of plates

move the beam horizontally from one side to another.–

• These two movements ( horizontal and vertical are independent of each other and thus the beam may positioned anywhere on the screen)

summary

H.T. supply

heater supply

y plates x plates

+-phosphor screen

anode

electron gun produces a beam

of electrons light produced on the screen by electron beam

a p.d. across the y plates deflects the

trace vertically

a p.d. across the x plates deflects the trace horizontally

Cathode Ray tube

• The main parts of a CRT

– Electron gun assembly

– Deflection plate assembly

– Fluorescent Screen

– Glass Envelop

– Base, through which connections are made to various parts

Measurment and Instrumentation

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