THE INDIAN ENGINEERING COLLEGE
DEPARTMENT OF ELECTRICAL AND ELECTRONICS
ENGINEERING
EE-33 MEASURMENTS AND INSTRUMENTATION
UNIT: 1- THEORY OF MEASUREMENT
1, When are static characteristics important ?
Static characteristics are important for measurement of
quantities that don’t vary with time or quantities that vary with time very slowly.
2, What is standard? What are different types of standards?
Standard is a physical representation of a unit of
measurement. It is used to obtain the values of physical properties of other equipment by
comparison methods.
Different types of standards are,
1, International standards
2, primary standards
3, secondary standards
4,Working standards.
3, What is the function of manipulation element in a measurement system?
The function is to manipulate
the signal presented to it preserving the original nature of the signal. It just changes the
numerical value of signal. For e.g : an electronic amplifies which just amplifies a small
voltage applied a small voltage applied to it as an input.
4, What are primary standards ? Where are they used?
These are highly accurate absolute standards
are maintained at National Standard Laboratories in different countries. These standards
representing fundamental units as well as same electricals mechanised derived units are
calibrated independently.
The main function is the calibration and verification of secondary
standards.
5, What is meant by accuracy of an instrument?
It is the degree of closeness with which the instrument
reading approaches the true value of the quantity to be measured is called accuracy.
6, Define international standard for Ohm?
The international standard for ohm is measured in 1
mm of mercury. Which are maintained at the international Bureau of Weights and
measures at serves.
7, Distinguish between the direct and indirect methods of measurements.
Direct method: In these methods, the unknown quantity is directly compared against a
standard. The result is expressed as a numerical number and a unit. The standard, in fact
is a physical embodiment of a unit.
Indirect method: These methods in most of the cases, are inaccurate because they
involve human factors. They are also less sensitive.
8, With one example explain ‘Instrumental Errors’.
These errors arise due to three main reasons.
1. Due to inherent short comings in the instruments.
2. Due to misuse of the instruments.
3. Due to loading effects of instruments.
e.g., If the spring of a permanent magnet instruments has become weak, the instrument
will always read high.
9, What is the importance of static characteristics of system?
Some applications involve the measurement of
quantities that are either constant or vary slowly with time. Under these conditions, it is
possible to define a set of criteria that gives a meaning description of quality of
measurement without interfering with dynamic description that involve the use of the
differential equations. These criteria are called static characteristics.
10, What is significance of calibration?
Calibration is the process of making an adjustment or making a
scale so that the readings of an instrument agree with the accepted and certified standard.
The calibration offers a guaranteed to the device or instrument that is
operating with required accuracy under the stipulated environmental conditions.
11, What is the importance of dynamic characteristic of system?
Invariably measurement systems, especially in
Industrial, aerospace and biological applications are subjected to inputs that vary with
time. The input varies from instant to instant and therefore, so does the output, the
behaviour of the system under such conditions is described by its dynamic response.
12, Why must instruments be calibrated?
Calibration of all instruments is important since it affords
the opportunity to check the instrument against a known standard and subsequently to
find errors and accuracy. Calibration procedures involves a comparison for the particular
instrument with either [1] Primary Standard, [2] Secondary Standard with a higher
accuracy than the instrument to be calibrated, [3] an Instrument of known accuracy.
13, List three main functional elements in the most measurement system.
1. Primary sensing element/variable conversion element
2. A detector,
3. An intermediate transfer device,
4. An Indicator, recorder [or] a storage device data presentation element.
14, Define the static error of an instrument or measurement system.
Difference between the measured value and the true of the quantity.
δ=Am-At;
ΔA=error value
Am= measured value quantity
At = true value.
15, Any two advantages of electronic measurement?
1. Most of the quantities can be converted by transducers in to the electrical or
electronic signals.
2. an electrical signal can be amplified, filtered, multiplexed, sampled and
measured.
16, Define primary sensing element ?
An element of an instrument which makes first the contact with the
quantity measured is called primary sensing element.
17, Define accuracy?
It’s the degree of closeness with which the instrument reading
approaches the true value of the quantity to be measured. It indicates the ability of
instrument to indicate the true value of the quqntity.
18,Define precision?
It’s the measure of consistency or repetability of measurements.
19, Define error?
The most important static characteristics of an instrument is it’s accuracy,
which is generally expressed in terms of the error called static error.
20, Define sensitivity and Resolution?
It’s defined as the ratio of the changes in the output of an instrument to
a change in the value of the quantity to be measured.
Sensitivity=I.C.output
I.C.input
Sensitivity= Δqo/Δqi
Resolution:
It is a smallest increment of quantity being measured which can be
detected with certainity by an instrument.
21, Define Threshold?
If the input quantity is slowly varied from zero onwards the o/p does not
change until some minimum value of the i/p is exceeded. This minimum value of the
input is called threshold.
22, Define linearity?
It’s defined as the ability to reproduce the i/p characteristics
symmetrically and linearly. Graphically such relationship b/w input and output is
represented by a straight line.
23, Define Zero Drift?
It is defined as the deviation in the instrument out put with time from it
is zero value when the variable to be measured is constant . the whole instrument
calibration may gradually shift by the same amount.
24, Define stability?
The ability of an instrument to retain its specified operating life and the
storage life is defined as its stability.
25, What are the different types of standards ?
1.International Standards
2. Primary Standards
3. Secondary standards
4.Working standards.
UNIT:2- ELECTRICAL AND ELECTRONICS INSTRUMENTS
1, Which torque is absent in energy meter ? why?
Controlling torque is absent in an energy meter . as the disc of energy
meter has to rotate continuously and there is no need to rest its position the controlling
torque is not required.
2, Explain the principle of digital phasemeter ?
A phasemeter is used to measure the phase difference between two
signals .Two signals of same frequency is applied to the meter and the are shaped to a
square waveform with out any change in there phase relationship which is required to be
measured.
3, Why the PMMC instruments are not used for ac measurements?
In ac measurement the torque produced on coil is reversing which
can not give accurate readings . Hence PMMC instruments are not used for
measurements .
4. What precaution must be taken while using CT and why?
As the turns ratio of C.T is such that it reduces secondary current
that it step the voltage at secondary. If secondary is kept open such as high voltage is
dangerous . produces excessive core losses and heating the core beyond the limits hence
secondary of C.T should not be kept open but should be shorted or must be connected in
series with a few resistance coil.
5, State the principle of digital volt meter ?
The digital volt meter generally referred as DVM, convert the
analog signals in to digital and display the voltages to be measured as discrete numerical
Instead of pointer deflection , on the digital display such voltmeters can be used to
measure a.c and d.c voltage and also to measure the quantities like pressure temperature
etc. using proper transducer and signal conditioning circuit
6, Give the importance of iron loss measurement?
It is most commonly used for measurement of iron loss in strip
material . The strip material to be tested is assembled as a closed magnet circuit in the
form of square , this arrangement is known as magnetic square .
7, Explain the principle analog type electrical instruments?
An analog device is one in which the out put or display is the
continuous function of time and bears a constant relation its input . Analog instrument
find extensive using in present day applications although digital in instrument are
increasing in number and applications.
8, How a PMMC meter can be used as voltmeter and ammeter?
Voltmeter: A d’Arsonval basic meter movement is converted in to a volt meter by
connecting a series resistance if it. This series resistance as known as multiplex . the
combination of meter movement and the multiplier is put across the circuit whose
voltage is to be measured ammeter.
9, What is ampere hour and watt –hour?
Watt hour is the unit of electric Energy.
Ampere hour rating: All ratings of the battery fells about how much amount of
current it can supply for hour . For example 80 AH means the battery will supply 80 A
for 1 hour.
10, what is the need to evaluate phase-angle error in instrument transformer?
Phase angle error depends on the components of exciting
current load current i.e;, secondary current and power factor . this error does not affect
the measurement of only current or voltage but do affect at the time of power and energy
measurements so we should evaluate the phase angle error to measure the accurate
readings.
11, What are the advantages of digital instruments over analog instruments?
1. Digital instruments Record the information in digital form.
2. The digital information is stored on punched cards , magnetic tape recorders
type written pages floppies.
3. They provides high quality records minimizing the operators work.
12, How are resistors and diodes checked using digital multi meters ?
To measure the resistances a constant current source is used The known
current is passed through the known resistance. The voltage drop across the resistance is
applied to analog to digital converter hence providing the display of value of the
unknown resistance.
13, How are the analog instruments classified on the basis of method used for
comparing the unknown quantity?
1. Direct measuring instruments
2. Comparison instruments.
14, Give the advantages of moving iron meters?
1. universal use
2. Less Friction errors
3.Chepness
4. Accuracy.
15, Any two advantages of PMMC instruments?
1. It has uniform scale .
2. The sensitivity is very high.
3. It has high accuracy.
4. Instrument is free from hysteresis error.
5. Extension of instrument range is possible.
16, Define frequency error?
These are related to a.c operation of the instrument . The change in
frequency affects the reactance of the working coil and also affects the magnitude of the
eddy current . This causes errors in the instruments.
17, Define multi range ammeters?
The range of the basic d.c ammeter can be extended by using number of
shunts and a selector switch. Such a meter is called multi range ammeter.
18, Define multi range volt meters?
The range of the basic d.c. volt meter can be extended by using
number of multipliers and a selector switch. Such a meter is called multi range volt
meter.
19, Define sensitivity of volt meters?
In a multi range voltmeters the ratio of the total resistance Rt to
the voltage range remains same. The ratio is nothing but the reciprocal of the full scale
deflection current of the meter i.e, 1/Im. This value is called sensitivity of the volt meter.
S= 1/ full scale deflection current
20, What are the requirements of a multiplier?
1. There resistance should not change with time.
2. The change in there resistance with temperature should be small.
3. They should be non inductively wound for a.c. meters
21, Define moving system?
The moving coil is wounded on an aluminium spindle. It consists of
counter weight and pointer. Some times a suspension may be used in case a height
accuracy is desired.
22, Any two advantages of elecctro dynamic instruments?
1, They have a precision grade accuracy.
2. Free from hysteresis errors.
3. Low power consumption
4. Light in weight.
23, Define temperature error?
The temperature errors are caused due to the self heating of the coil
which causes change in the resistance of the coil . thus temperature compensating
resistors can be used in the presise instrument to eliminate the temperature errors.
24,Define steady state tests?
The flux in the air gap plays an important role in the operation of various
electrical equipments. Such a flux is measured using steady state tests. Such tests give
steady state value of the flux in the air gap of magnetic material.
25, Differences between flux meters and ballistic galvanometer?
No
Flux Meter
Galvanometer
1,
Controlling torque is very small
It’s very High
2,
Heavy Electromagnatic dambing
It’s not Heavy
3,
Less sensitive
More Sensitive
4,
Less Accurate
More Accurate
UNIT: 3 – COMPARISON METHODS OF MEASUREMENTS
1, Name of the different types filters used in instrumentation system?
Broadly filters are classified as: Active filter and passive filter
Both active and passive filter are further classified as 1. Low pass filter 2. high pass
filter 3. Band pass filter 4. Band pass filter
2, What is multiplexing ?
Multiplexing means mixing (or) combining of different signals. In data
processing it is required that number of analog signals are combined (or) multiplexed in
to a single digital and vice versa.
3, What are the requirements of good instrumentation amplifier?
1.
2.
3.
4.
5.
6.
7.
8.
Finite, accurate and stable gain
Easy gain adjustment
High input impedance
Low input impedance
High CMRR
Low power consumption
Low thermal drifts
High slew rate
4,What is quantization error?
In A/D conversion there exists an unavoidable uncertainty about the exact
value of input. This uncertainty is specified as quantization error.
Qe = ViFs/(2^n-1)
5, Give some application of Wheatstones bridge?
1.
2. Its used for measurement of medium resistance.
3. It has been in use longer than almost any electrical measuring instrument.
6, Explain any technical parameters to be considered in grounding?
1, Resistance 2, Reactance
7, What are active and passive bridge circuits?
The elements used in passive bridge circuit are R,L,C
A.C.Bridges:
Maxwell’s bridge , Hay’s bridges ,Scherring bridge DC Bridges.
Whestone Bridge, Kelvin Bridge.
8, What are leakage current effects?
Leakage current produce leakage reactance which increase ratio
error.
9, Derive the condition for sustained oscillation in feed back oscillators?
1, The total phase shift around a loop is precisely 0ºor 360º or integral multiple
of 2π.
2, Then the product of the open loop gain of the amplifier and the feed fact
factor is unity.
10, What is electro magnet interference in instruments?
The interference caused due to electromagnetic waves is called
electro magnetic interference. So all the sensitive circuits from a measurement system
must be protected from radio frequency signals. Measurement system must be protected
from radio frequency signals .
11, What is the roll of toroidal core in a trapped ratio transformer?
Readuces magnetic circuit and its winding has minimum leakage
reactance resulting to perfect coupling.
12, What is transformer ratio bridge ?
The transformer ratio bridge use as a ratio transformer which
is highly accurate an versatile . Thus conventional A.C.bridges are now getting replaced
by the transformer ratio bridges.
13, What are the classification external interface signal ?
1. Capacitive interference
2. Inductive interference
3. Electromagnetic interference
4. conductively interference
5. ground loop interference
14, Define shielding ?
The property of electro magnetic waves is that such wave travel
consisting of both electric and magnetic components and get haulted if one of the two
components eleminted . The shield which can eliminate electrostatic fields can be
designed easily .Which is already discuses in capacitive interference shielding
15, What is guard shield ?
In the method of input guarding the complete measuring or input
circuit unit of a differential amplifier is placed inn side a metallic guard. The shield of
metal used for this purpose is called guard shield.
16, What is standardisation of potentiometer?
Standardisation of potentiometer is a process of adjusting the
working current supplied by supply battery such that the voltage droop across a portion of
sliding wire matches with the standard reference source.
17, Advantages of Duo-range potentiometer ?
1. Due to the dual range ,the precision of reading is
increased by one decimal point
2. Due to the inherent accuracy of dial resister as
compared to that of slid wire , The accuracy pf reading
is increased .
18, What are the reduction of ground interference signal ?
There are number of ways by which ground loop interference signal
can be reduce . These techniques are
1. Single point grounding
2. Use of differential input amplifiers
3. Input guarding
4. using doubly shielded cables .
19, Define transformer double ratio bridges ?
In all the transformer bridges discussed above the balance
condition is detected by the detector as voltage across it is zero at current through it is
zero at the balance conduction . This is identical to the detectors used in conventional
A.C bridges.
20, What are advantages of Andersons ‘bridge?
1. Can be used for accurate measurement of capacitance in
tames of inductance.
2. Other bridges require variable capacitor but a fixed
capacitor can used for Andersons’ bridge
3. The bridge is easy to balance form convergence point if
view compared to Maxwell’s in case of low value of Q
21, What are the disadvantages of Anderson’s Bridge ?
1. Its more complicated than other bridges
2. Uses more number of components
3. Balance equations is also complicated to drive.
22, What are the disadvantages of Maxwell’s bridge?
1. The balance equation is independent of losses associated with
inductance.
2. The balance equation is independent of frequency of measurement
3. The scale of resistance can be calibrated to read the inductance
directly.
4. The scale of R1 can be calibrated to read the Q value directly.
23, Define Maxwell’s bridge?
Maxwell’s bridge can be used to measure inductance by comparison
either with a variable standard self inductance or with a standard variable capacitance
.These two measurements can be done by using the Maxwell’s bridge in two different
forms.
24, What are the advantages of Wheatstone Bridge ?
1. The results are not dependent on the calibration and characteristics of
galvano meter as it works on null deflection
2. The source E.M.F and in accuracies due to the source fluctuations do not
affect the balance of the bridge. Hence the corresponding errors are
completely avoided.
3. Due to the null deflection method used, the accuracy and sensitivity is
higher than direct deflection meter.
25, What are the applications of Wheatstone Bridge?
1. Its used to measure the D.C resistance of various types of wires for
the purpose of quality control of wire
2. It’s used to measure the resistance of motor winding , relay coils
etc….
3. It’s used by the telephone company to locate the cable faults. The
faults may be of the type line to line short or line to ground short.
UNIT:4-STORAGE AND DISPLAY DEVICE
1, State the features of ink-jet printers.?
1. They can print from two to four pages per minute
2. Resolution is about 360 dots per inch, there fore better printing
quality is achieved
3. The operating cost is quite low, the only part that needs
replacement is the ink-jet cartridge.
2, Diffferentiate between LED and LCD ?
No
LED
LCD
1
It emits light
They don’t emit light, but rather alter
externally generated illumination .
2
They can be mounted easily at any
place
Difficult to mount.
3
They have longer life time
Comparatively there life time is shorter.
3, What are the various methods of recording data?
Electronic recorders may be classified as
1, Analog Recorders :
 Graphic Recorders
 Oscillographic Recorders
 Magnatic tape recorders
2, Digital Recorders:
 Incremented Digital Recorders
 Synchronous Digital Recorders
4, In what ways line printers are advantages over dot matrix printer?
Line printer prints a complete line at a time, the printing the
speed vary from 150 lines to 2500 lines per minute with 96 to 100 characters on one line.
But dot matrix printer print one character at a time.
In line printers, The printing quality and its speed are better but in dot matrix printers ,
the printing quality is poor as characters are formed by combination of dots
5, What’s mean by deflection sensitivity of a CRT ?
The deflection sensitivity of a CRT is defined as deflection of the screen per unit
deflection voltage.
Deflection sensitivity = D/ Ed meter per volt.
6, Write two advantages of LED in electronic displays.
1. LED’s are miniature in size and they can be stacked together to form
numeric and alphanumeric displace in high density matrix.
2. The switching time is less then 1 ns and there fore they very useful where
dynamic operation of large number of arrays is involved
7, Explain the characteristics of time domain out put device using in measurements .
C(t)= out put
R(t) =input
Ao and Bo are constant .
C(t)=(Bo/Ao)R(t)
If the values of the quantity are to be taken as a function of time the indicating
instruments or the digital displays unit are no longer satisfactory expect for application
where the out put varies at a very slow rate.
8, Explain the following terms as applied to digital displays 3½ digit and 4½ digit
displays?
In practice a fourth digit usually capable of indicating either 0 or 1 only,
displaced to the left of active digits these permits giving above 999 to 1999 to give over
lab between rages for convines . This is called over ranging. This type of dis play is
known as 3½ digit displays.
9, Give the principle of LCD type display device
.
The term liquid crystal refers to the fact that these compounds have a
crystalline arrangement of molecules, yet they flow like a liquid. Liquid crystal displays
do not emit or generate light, but rather alter externally generated illumination. Their
ability to modulate light when electrical signal is applied has made them very use ful in
that panel display technology.
10, Write briefly in pink plotter .
The plotter is used to draw the graphs of various parameter.
11, Explain briefly on magnetic tapes.
The magnetic tape is made up of thin sheet of tough and dimensionally
stable plastic ribbon one side of these plastic ribbon is coated by powdered iron oxide
particles. A typical tape is 12.7 mm wide and 24.4 µm thick. The magnetic tape is wound
around a real. This tape is transferred from one real to another ,when the tape passes
across the gir gap the magnetic pattern is created in accordance with variation of
recording camera to reproduce this pattern, the same tape with some recorded pattern is
passed across another magnetic head in which voltage is induced. This voltage induced in
accordance with the magnetic pattern.
12, What is the magnetic principle used in computer data storage?
Voltage induced on the tape is proportional to the rate of range of flux
linkages.
13, Compare LED and LCD.
No
1
2
3
4
LED
High power consumption
Costlier
Faster
Small in size
LCD
Low power consumption
Cheaper
Slower
Bigger in size.
14, Basic components of tape Recorder?
1.
2.
3.
4.
5.
Recording head
Magnetic Tape
Reproducing Head
Tape Transport Mechanism
Conditioning Devices
15, Advantages of Digital plotters?
1. Simultaneous storage of number of input signals is
possible.
2. The data can be plotted using multi pen plotting system
3. The recorder can record or draw grids , axis.
4. The hardware and software interface provides better
capabilities.
16,What are the methods of recording?
1. Direct Recording
2. Frequency modulation Recording
3. Pulse Duration Modulation Recording.
17, Define Direct Recording?
This method of recording is the simplest one. This method
usually requires one tape track for each channel. The input signal to be recorded is
amplified and mixed with high frequency bias. This signal is then fed to recording head
as recording current.
18, What are the disadvantages of recording?
1.
2.
3.
4.
The tape speed fluctuations affect the recording.
FM systems have limited frequency response
For FM recording high tape speed are required
It is comparatively expensive.
19, What are the characteristics of general purpose oscilloscope?
1.
2.
3.
4.
5.
It gives colour to which human eye response is maximum.
It gives short persistence required to avoid multiple image display.
It has high burn resistance to avoid the accidental damage.
Its illumination level is high.
It provides high writing speed.
20, Define glass tube?
All the components of a CRT are enclosed in an evacuated glass tube
called envelop. This allows the emitted electrons to move about freely from one end of
the tube to the other end.
21, Comparison of mesh and phosphor storage?
No
Mesh Storage
Phosphor Storage
1
Storage target and display target are
different
Storage and Display target is same
2
Variable persistence is possible
Variable persistence is not possible
3
Grey scales of half tones are
possible
Half tones are not possible
22, what are the advantages of digital storage oscilloscope?
1.
2.
3.
4.
5.
It’s easier to operate and has more capability.
The storage time is infinite
The curser measurement is possible.
The X-Y plots, B-H curve, P-V diagrams can be displayed.
The pre trigger viewing feature allows to display the waveform
before trigger pulse .
23, Define acquisition methods?
In the digital storage oscilloscope, Its necessary to capture the digital
signal and store it. Depending upon the particular application, There are three different
acquisition methods used in the digital storage oscilloscope .
24, Advantages of LCD’s?
1.
2. Less power consumption
3. Low cost
4. Uniform Brightness with good contrast
5. Low operating voltage and current
25, Disadvantages of LCD’s?
1. Poor reliability
2.
3.
4.
5.
Limited temperature range.
Poor visibility in low ambient temperature.
Slow speed
Requires in A.C drive
UNIT:5- TRANSDUCERS AND DATA ACQUISITION SYSTEM’S
1, Which are the materials used in piezo electric transducers?
1.
2.
3.
4.
5.
Quartz
Rochelle sales
Tourmaline
Barium totonale
Lithium sulphate
2, Name the traducers used for sensing acceleration?
1. Accelero meter
2. Speedometer
3,.What is pot? Is it active are passive transducer?
Pot is potentiometric resistive transducer consisting a wise wound resistive
component along with a sliding conduct called wiper.
Pot is a passive transducer as change in resistance is effective only
if when external excitation is applied.
4,What is the principle of electro magnetic flow meter?
Electro magnetic flow meter is based on the principle of
electromagnetic induction given by Faraday’s law.
The E.M.F is given by
E=B.l.V
Where B- Flux density
l- Distance between two electrodes
VVelocity of flowing fluid.
5, Give the factors to be considered for selecting a transducer.
1. According to principle used in transduction
2. Basis of the o/p which may be continuous function of time or
the o/p may be discrete steps
6,Why is an A/D converter usually considered as an encoder?
When the analog information is simple and more accurately
converted in to digital form its enable the information can considered as an encoder.
7,Defgine inverse transducer with example?
An inverse transducer is defined as device which converts an
electric quantity in to a non electrical quantity. It’s a precision actuator Which has
electrical input and a low power non electrical out put.
8,Explaine the Principle of piezoelectric transducer and name a two piezoelectric
material?
If a varying potential is applied to the proper axis of the crystal ,
it change the dimension of the crystal thereby deforming it. This effect is known as piezoelectric effect.
1. Rochelle salts
2. Ammonium dihydrogen phosphate
9, State piezoelectric effect ?
When two opposite faces of a thin slice of certain crustes are subjected
to a mechanical then opposite chargers are developed on the two forces of slice. The
magnitude of the electric potential between the two faces is professional deformation is
produced. This phenomenon is called piezoelectric effect.
10,Whgat is the o/p expected out of an LVDT provided with unidirectional
excitation, While measuring a displacement of 3 cm?
In general 1mm displacement produce the voltage of 300 mv
3 cm produce = 30*300=mv
= 9000mv=9v.
11,How are strain gauge used for pressure measurement?
If a metal conductor is stretched or compressed, its resistance changes
on account of the fact that both length and diameter of the conductor change the moving
principle is piezo resistive effect.
12, What is meant by quantization error?
In ADC , The binary output is 001 for all the values of V/i
Between ¼ $ ½ volt . there is an un certainty about the exat value vi When the o/p is
o11. This un certainty is specified as Quantization error. Its value is +_ ½ LSB
Qe = ViFs / (2ⁿ- 1)2.
13,How the transducers are classified on the basis of principle of transduction?
1. Linear displacement
2. Rotary displacement.
14, What are the essential function operations of a digital data acquisition system?
1.
2.
3.
4.
Data handling
Making measurement
Data conversion
Internal programming and control.
15, What are the advantages of electrical transducers?
1. The power requirement of transducers is very small. The
electrical systems can be controlled with a small level of
power.
2. The reduced effects of friction and other mechanical
nonlinearities.
3. The reduced effects of mass inertia problems.
16, Define Analog transducers?
These transducers convert the input quantity into an analog output
which is a continuous function of time. A strain gauge, LVDT, thermocouples or
thermistors are called analog transducers as they produce an output which is a
continuous function of time.
17,Define Digital transducers?
Digital transducers produce an electrical output in the form of pulses which
forms an unique code. Unique code is generated for each discrete value sensed.
18,What are the characteristics of transducers?
1. Accuracy
2. Ruggedness
3. Linearity
4. Repeatability
5. High output
6. High Stability and Reliability
7. Sensitivity
8. Dynamic Range
9. Size
10. Speed of Response
19, what are the advantages of semi conductor strain gauge?
1. It has a high gauge factor of about 130, which allows
measurement of very small strain, of the order of 0.01 micro
strain
2. Hysteresis characterstics of semi conductors strain gauge
excellent ; i.e, less than 0.05%
20,What are the disadvantages of semi conductor strain gauge?
1. The semi conductor strain gauge is sensitive to changes in temperature.
2. The linearity of the gauge is poor.
3. The gauge is more expensive.
21, What are the advantages of RTD?
1.
2.
3.
4.
The measurement is accurate
They are suitable for remote indication.
They are smaller in size.
They have stability over long periods on time.
22, What are the limitations of thermistors ?
1. The resistance versus temperature characteristics is highly non liner
2. Not suitable over a wide temperature range.
23, Define active transducers?
The transducers which generate and electrical signal directly in response
to the physical parameter with out requiring external power for the operation are called
active transducer.
24, Define thermocouple?
Thermo electric transducer is a temperature transducer which convert
thermal energy in to and electrical energy. The most commonly used thermo electric
transducer is thermocouple.
25, Applications of thermistor?
1.
2.
3.
4.
5.
Useful for temperature transducer
Ideal for remote measurement or control
For providing time delays
For measurement of composition of gases
For vacuum measurement’s.