Process Control and Instrumentation Flashcards
Which of the following is an undesirable dynamic characteristic of an instrument ?
Time lag
Which of the following is not the triple point of water ?
32°R
Load cells are used for the measurement of
weight
Which of the following is the dynamic characteristics of an instrument ?
Fidelity
Pick out the wrong statement.
CO2 is the strongest paramagnetic gas.
The __________ of a vapor pressure thermometer is a functioning element.
pointer
A negative gain margin expressed in decibels means a/an __________ system.
unstable
Thermistor, which has high temperature co-efficient of resistivity, is used as the sensing element in resistance thermometer. It is a/an
solid semi-conductor
Flapper nozzle is used in a/an __________ controller.
pneumatic
Typical specifications for design stipulates the gain margin and phase margin to be respectively
> 1.7 and > 30°
Working principle of radiation pyrometer is based on the
Stafan-Boltzman law
Which of the following relates the emf. generated in a single homogeneous wire to the temperature difference ?
Thomson effect
Dilute wine was used as a thermometric liquid initially to develop temperature scale. First emperical temperature scale developed was the __________ scale.
Fahrenheit
Which of the following is a desirable characteristic of an instrument ?
High fidelity
The operation of a rotameter is based on
variable flow area.
The temperature of tempering oil baths maintained at 400°C during heat treatment of steel is measured by a/an __________ thermocouple.
iron-constantan
Which of the following temperature measuring instruments need not touch the object whose temperature is being measured ?
Radiation/infrared pyrometer
Thermal conductivity measurement com-prises the working principle of a
CO2 analyser
Response of a system to a sinusoidal input is called __________ response.
frequency
The closed loop pole of a stable second order system could be
both real and negative.
Smoke density of the flue gas going out of the chimney is measured by a
photo electric cell
Pick out the first order system from among the following.
Mercury in glass thermometer kept in boiling water.
The maximum service temperature for fibre glass used as thermocouple wire insulation material is __________ °C.
500
Volumetric expansion is the working principle of the __________ thermometers.
mercury in glass
Zirconia probe is used for the continuous measurment of __________ flue gases going out of the furnace.
oxygen in
Compositional analysis of __________ is done using mass spectrometer.
an isotope
The function of a transducer is to
convert the primary signal into a more useful quantity, usually an electric impulse.
Nichol’s chart deals with
closed loop values vs. open loop values.
Which of the following thermocouples will give the highest output for the same value of hot and cold junction temperature ?
Chromel-constantan.
A proportional controller with a gain of Kc is used to control a first order process. The offset will increase, if
Kc is reduced.
__________ is undesirable in thermocouples used in industries,
Non-linear relation of emf to temperature
Continuous shell temperature measurement in a liquid-liquid heat exchanger is done by a
thermocouple
The __________ of a vapor pressure thermometer is a secondary element.
Bourdon tube
Emf developed by a thermocouple, while measuring a temperature of 600°C is about 5.5 mV. The type of thermocouple used is
platinum-platinum+rhodium
Which of the following relates the absorption & evolution of heat at the junctions of a thermocouple to the current flow in the circuit?
Peltier effect
In a shell and tube heat exchanger, the flow rate of heating/cooling fluid is the __________ variable.
manipulated
A non-linear chemical system is exemplified by a/an
non-isothermal CSTR
Gas chromatography is used for the measurement of
concentration
Which of the following thermocouples can measure the maximum temperature ?
Tungsten-molybdenum
Radiation pyrometers as compared to thermocouples
can measure higher temperature.
Liquid flow rate in a small channel is best measured by a/an
pitot tube
Specific gravity of a liquid can not be measured by a/an
anemometer
__________ temperature scale assigns 0° to the ‘ice point’ and 80° to the ‘steam point’.
Reumur
Dead zone is the
maximum change in the variable that does not change the reading of the instrument.
Which of the following thermometers is not suitable for distant reading upto 60 metres?
Mercury in glass thermometer
Degree to which an instrument indicates the changes in measured variable without dynamic error is called its
fidielity
Thermistors are made of
metal oxides
A barometer measures the __________ pressure.
absolute
Humidity of air can be determined by a
sling psychrometer
Thermocouple in a thermal well behaves as a true
multiple first order system.
Working principle of disappearing filament type optical pyrometer is based on the
Wien’s law
Strain gage uses an electrical conductor wire, which when elastically stretched increases in length and reduces in diameter. Both these dimensional changes result in __________ in the electrical resistance of the wire.
increase
The __________ of a vapor pressure thermometer is a primary element.
bulb
The time constant of a first order process with resistance R and capacitance C is
RC
A sinusoidal variation in the input passing through a linear first order system
gets attenuated (magnitude decreases).
Pick out the most suitable instrument for measuring temperature in the range of-40 to 425°C
bimetallic thermometer
Relationship between absorption/evolution of heat at the thermocouple junctions and the current flow in the circuit is given by __________ effect.
Peltier
Configuration of Bourdon spring tube is never made of __________ shape.
circular
In a closed loop system, the process to be controlled is an integrating process with transfer function l/2s. The controller proposed to be used in an integral controller with transfer function 1/T1s. When a step change in set point is applied to such a closed loop system, the controlled variable will exhibit
underdamped response.
Measurement of pressure in ammonia reactor is done by
Bourdon gauge
The fluid used in hydraulic controller is
oil
Flow rate of a river is measured by a/an
vane meter
Flow rate of those fluids which are insensitive to changes in their density, viscosity or flow velocity profile can be best measured by a
magnetic flowmeter
“A control system is unstable, if the open loop frequency response exhibits an amplitude ratio exceeding unity at the crossover frequency.” This is __________ criterion.
Bode stability
Feed forward controller accounts for the __________ changes.
load
Which thermocouple can be used to measure a temperature of around 1400°C ?
Platinum-platinum+rhodium
Concentration of sugar solution can be determined by the
polarimetry
Which of the following filled system expansion thermometer has the capability to measure the lowest temperature ?
Alcohol in glass thermometer
The temperature range for which copper resistance thermometer can be used is __________ °C
-200 to 150
Paramagnetism method is not used for the composition determination of __________ in gases.
carbon dioxide
An amplitude ratio of 0.1 corresponds to __________ decibels.
-20
For increased speed of response of an expansion pressure spring thermometer, the thermometer bulb should have a
all’a’, ‘b’ & ‘c’.
Pressure of 0.0001 absolute psi can be measured by __________ gauge.
Mcloid
Pirani gauge is used for the measurement of
high vacuum.
The __________ of the fluid contained in the temperature sensing element (i.e., bulb) of filled system thermometers changes with change in temperature.
all (a), (b) and (c)
The characteristic equation for the control system with a closed loop transfer function G1/1 + G2 is given by 1 + G2 = 0. The characteristic equation for the control system
all ‘a’, ‘b’ & ‘c’
__________ thermometer can not measure sub-zero (< 0° C) temperature,
Bimetallic
Starting temperature of optical radiation pyrometer is __________ °C.
800
Liquid argon level in a pressurised storage tank (at 3 kg/cm2 ) is measured by a/an
differential pressure gage
Which of the systems having following transfer functions is stable?
1/(s2 + 2s + 2)
What is the dynamic error in a critically damped second order instrument for a ramp input (At) ?
2 AT
The deflection of the free end of the bimetallic strips in a bimetallic thermometer with temperature is nearly
linear
Alphatron measures pressure __________ microns.
> 3
What is the ratio of output amplitude to input amplitude for a sinusoidal forcing function in a first order system ?
< 1
The term analogous to the electrical current in a thermal system is the
heat flow rate
Reset rate is the another term used for __________ time.
integral
Continuous measurement of moisture in paper is done by
high resistance Wheatstone’s bridge circuit.
Psychrometer determines the
humidity of gases
A mercury barometer measures the __________ pressure.
atmospheric
Positioning controllers are used for
high loads
The amplitude ratio for the sinusoidal response of a __________ is 1.
transportation lag
The response of two tanks of same size and resistance in series is
critically damped
The amplitude ratio for the sinusoidal response of __________ is < 1.
first order system
Which of the following is a ‘contact’ pyrometer ?
resistance pyrometer
Which of the following is not a speed measuring instrument ?
Psychrometer
Measurement of sub-zero Celcius temperature in industry is done most commonly by
resistance thermometers
Use of I-control along with P-control facilitates
elimination of offset
Turbine flow meters are suitable for
both (b) and (c).
Liquid discharge from a tank or reservoir can not be measured by
orificemeters
Which of the following is not a mechanical pressure sensing element ?
U-tube
__________ are analysed using a polarograph.
Solids
Which of the following judges the accuracy of an instrument ?
Static error
On-off controllers are normally used for
low loads
Magnetic flowmeters are generally not used for the velocity/flow measurement of hydrocarbons due to their
low electrical conductivity.
Pressure of 0.01 psi (absolute) can be measured by __________ gauge.
Mcloid
High temperature of around 2000°C of incandescent gas mantles is measured by a/an
radiation pyrometer.
The unit step response of the transfer function 1/(s2 + 2s + 3)
has a damped oscillatory characteristics.
Which of the following does not figure in the list of seven substances selected for international temperature scale ?
Zinc (B.P) and mercury (F.P)
The time constant of a unity gain, first order plus time delay process is 5 min. If the phase lag at a frequency of 0.2 rad/min is 60°, then the dead time (in minutes) is
5π/12
A constant volume gas thermometer employing __________ is used to measure sub-zero (i.e., < 0° C) temperature.
helium
pH meter has
two cells
Routh test
cannot be used to test the stability of a control system containing transportation lag.
When a bare thermocouple is covered by a protective sheath, the response becomes
slower and non-oscillatory.
What is the normal percentage of rhodium in platinum + rhodium element used in the thermocouple ?
13
Helium gas constant volume thermometer is suitable for the measurement of a temperature of __________ °C.
< 0
Vapour actuated pressure spring thermometer does not require ambient temperature compensation. Ambient temperature compensation is provided in gas or liquid expansion pressure spring thermometer by
all ‘a’, ‘b’ & ‘c’.
Bode diagram are generated from output response of the system subjected to which of the following input?
Sinusoidal
Which of the following thermocouples is the most suitable for measuring a temperature of about 1600°C in an oxidizing atmosphere ?
Platinum-platinum + rhodium
ercury thermometer can be used to measure the temperature upto __________ °C.
350
Working principle of mercury in glass thermometer is based on volumetric expansion of mercury with increase in temperature. Which of the following undergoes minimum volumetric expansion for a given temperature change ?
Mercury
Which of the following is not a differential pressure flow meter ?
Rotameter
Bourdon gauges are used for measuring pressure (kg/cm2 )
> 2 (gauge)
A photo electric device in which the resistance of the metal is directly proportional to the light striking on it, is known as photo-conductive cell. Photoelectric transducers are used for the measurement of those parameters, which can be used to produce variation in
light intensity
A typical example of a physical system with under damped characteristic is a
spring loaded diaphragm valve.
An aneroid barometer measures the __________ pressure.
absolute
A bolometer is
both (a) & (b).
The offset introduced by proportional controller with gain Kcin response of first order system can be reduced by
introducing integral control.
Thermal wells are used in the temperature measurement to
guard against corrosive and oxidising action on thermocouple materials
A system with a double pole at the origin is unstable since the corresponding term in the time domain
grows linearly with time.
To increase the speed of response of a pressure spring liquid or gas expansion thermometer, the clearance space between the thermometer bulb and the thermal well should not be filled with
air
In an exothermic chemical reactor, the manipulated variable is the flow rate of
coolant
Very low pressure is expressed in microns(μ), which is equal to __________ mm of Hg coloumn (absolute) at 0°C.
0.001
Thermal conductivity based continuous flue gas analyser makes use of varying thermal conductivity of the constituents of flue gases. Which of the following constituents of flue gases has the maximum thermal conductivity ?
CO2
Emf generated in a thermocouple depends on the temperature
difference between hot and cold junctions.
Working principle of mercury in glass thermometer is based on the __________ of mercury with increase in temperature.
volumetric expansion
Radiation thermometer can not measure the temperature
of liquid oxygen.
Temperature measurement by optical pyrometer is done above __________ point, which is 1063°C.
gold
Continuous flue gas analyser makes use of paramagnetic properties of some of its constituents, which move towards the strongest part of the magnetic field thus displacing diamagnetic gases. Which of the following gases is diamagnetic ?
CO2
A first order system with a time constant of 1 min is subjected to frequency response analysis. At an input frequency of 1 radian/min, the phase shift is
-45°
__________ stability method uses open loop transfer function.
Nyquist
Dilatometer is used to measure
contraction/expansion due to changes in temperature
Mass spectrometer is used for the composition analysis of
isotopes
A pyranometer is an instrument used for measuring the
global radiation.
All the thermocouples used for temperature measurement use dissimilar metal
wires
Composition of alloys can be determined by
polarograph
Optical activity of a solution can be determined using a
polarimeter
Stability of a control system containing a transportation lag can be best analyzed by
frequency response methods
Stabilizing time for the controllers is the time required for the response to reach __________ percent of its ultimate value.
95
Time constant is the
time taken by the controlled variable to reach 63.2% of its full change.
Mercury manometer (U-tube type) exemplifies a __________ order system.
second
Emf developed by a thermocouple while measuring a temperature of 400°C is 22 mV. The type of thermocouple used is
iron-constantan
Bode stability method uses __________ loop transfer function.
open
Working principle of bimetallic thermometers is difference in linear co-efficient of thermal expansion of two strips of different metals welded together. Which of the following has the maximum thermal co-efficient of linear expansion?
Brass
Which of the following is not a second order instrument ?
Bare mercury in glass thermometer.
Small furnace draught is accurately measured by an inclined tube manometer, in which the manometric liquid used most commonly is
paraffin
Specific conductance is defined as the reciprocal of resistance in ohms of 1c.c. of liquid at a specified temperature. Its value for distilled water is about __________ micro mho/cm3.
1
A simple pitot tube measures the
static pressure
For a feed back control system to be stable, the
poles of the closed loop transfer function should lie in the left half of the complex plane.
A mercury thermometer can not be used to measure the temperature below the freezing point of mercury, which is __________ °C.
-38.9
__________ controller has the maximum stabilizing time.
PI
Out of the following temperature measuring instruments, the measurement accuracy will be minimum for the
optical pyrometer.
Stalagmometer is used for the measurement of
surface tension
The deflection in diaphragm (which is used as pressure sensor in pneumatic and electronic instruments) is dependent on the metal thickness, its diameter (d) and shape & number of corrugations. Its deflection is proportional to
d4
Working principle of radiation pyrometer is based on the
stefan-Boltzman law
Liquid levels in autoclaves are measured by
differential float type manometer
E.m.f. generated by thermocouples is of the order of
millivolts
A pyrheliometer is an instrument used for measuring the
beam radiation.
__________ is the static characteristics of an instrument,
Drift
Phase lag of the frequency response of a second order system to a sinusoidal forcing function
approaches 180° asymptotically
Flow rate through an orifice is __________ the pressure differential.
proportional to the square root of
Dead zone in an instrument must be less than __________ percent of the scale.
0.2
Emission spectroscopy is used for
solids and metal analysis.
Gas analysis is commonly done using the
thermal conductivity cell
Thermal conductivity measurement is used for the determination of
CO2 percentage in the flue gas.
Presence of a small amount of water in the organic systems can be determined by the __________ method.
dielectric constant end loss factor
Thermal conductivity cell is the primary element of a/an __________ analyzer.
carbon dioxide
Zirconia probe is used for the measurement of
% O2 in flue gas.
__________ type of element is normally not used in the bimetallic thermometers.
Bourdon tube
The root locus method, a pole of a transfer function G(s) is the value of s for which G(s) approaches
∞
Suppose that the gain, time constant and dead time of a process with the following transfer function:Gc(s) = 10 exp( - 0.1s)/(0.5s + 1) are known with a possible error of ± 20% of their values. The largest permissible gain Kc of a proportional controller needs to be calculated below taking the values of process gain, time constant and dead time as
12, 0.6, 0.12
Process degree of freedom indicates __________ number of controllers to be used.
the maximum
Characteristic equation is the denominator of __________ loop transfer function.
closed
Operating range of a temperature measuring instrument is 800 to 1600°C. It could be a/an __________ pyrometer.
photoelectric
Polarograph is meant for the analysis of
solids
Which of the following fluid flow measuring devices can measure the largest flow rate ?
Weir
Flow rate of sludge is not measured by a/an
both(b)&(c)
In a shell and tube heat exchanger, the inlet temperature of heating/cooling fluid is the __________ variable.
load
Polarization of light forms the working principle of a
polarimeter
A bimetallic thermometer as compared to industrial mercury in glass thermometer has almost the same
all a, b & c.
Thermal wells used in temperature measurements should have
high transmissivity of radiation.
Which of the following flow-metering instruments is an area meter ?
Rotameter
Out of the following themocouple wire insulating material, the highest temperature rating is for
ceramic fibre
Which is the most suitable instrument for measuring pressure below 3 microns ?
Ionisation gauge
Photoelectric pyrometers are suitable in the temperature range of __________ °C.
800-1600
Routh stability method uses __________ loop transfer function.
closed
Pyrometry refers to the measurement of temperature
which is of higher magnitude.
Non-metallic diaphragm used as pressure sensor in instruments is generally made of
synthetic rubber
Response of a linear control system for a change in set point is called
servo problem
Hot wire anemometer is used for the measurement of
flow rates of fluids.
Which of the following thermocouples has the widest temperature measurement range ?
Platinum-platinum/rhodium
Temperature control of an exothermic chemical reaction taking place in a CSTR is done with the help of cooling water flowing in a jacket around the reactor. The types of valve and controller action to be recommended are
air to open valve with the controller indirect acting.
Bourdon tube is never made of
cast iron
An emf of the order of mV is generated when two solutions of different hydrogen ion concentration are separated by a thin glass wall”. This is the working principle of a
pH meter
Mcleoid gauge is used to measure the
vacuum
Bimetal strips are not used in
thermocouples.
When the damping co-efficient (ξ) is unity, the system is
Critically damped.
Nickel percentage in invar which is an iron-nickel alloy, and is used as a thermocouple material is
36
Silver point temperature is __________ °C.
960.5
A non-linear system will have __________ steady state values.
more than one
Which of the following is not a variable area flow meter ?
Magnetic flow meter
With increase in temperature, the electrical conductivity of the platinum used in the resistance thermometer
decreases
Sub-zero temperature (< 0°C) can be measured by a constant volume gas thermometer employing
helium
__________ is an example of distributed parameter system
Tubular reactor
Which of the following is not classified as a thermo electric pyrometer ?
Optical pyrometer (disappearing filament type)
Maximum differential pressure in liquid manometer is __________ psi.
30
Phase margin is equal to
180° - phase lag
Flow rate measurement of hostile acids and alkalis can be most suitably done by a/an
magnetic flow meter
Compositional analysis of flue gas coming out of a furnace in respect of O2 and CO2% can be continuously done by a/an
thermal conductivity cell
Thermisters which have a very high temperature co-efficient of resistivity belong to the class of solid called
semi conductors
The pressure sensing element of elastic type pressure gauge is never made in the form of a
strip
Liquid flow rate in an open channel can not be measured by a/an
orifice meter
The unit of ‘time constant’ of a system is the same as that of
time
Which of the following filled system expansion thermometers has the lowest positive temperature measurement capability ?
Alcohol in glass thermometer.
The term analogous to voltage in a single tank system is the
level of liquid.
In a shell and tube heat exchanger, the outlet temperature of heating/cooling fluid is the __________ variable.
controlled
Thermocouple is suitable for measuring
both high and low temperatures.
Liquid column manometers are used for measuring the pressure __________ kgf/cm2 .
< 3 (gage)
Cascade control means
more than one feed-back loop.
The level of a liquid under pressure can be determined using
differential pressure manometer
Temperature measurement range of iron-constantan thermocouple is 0 to 870°C. It can be used to measure sub zero temperature, because at lower temperature
both (b) and (c).
Which of the following is never used as an element of industrial resistance thermometer ?
Lead
A stable system is the one
for which the output response is bounded for all bounded input.
Which of the following shows maximum dip effect (indicating reverse direction of temperature change) ?
Mercury thermometer
Meleoid gauge measures the __________ pressure.
sub-atmospheric
Which of the following thermocouples is capable of measuring a temperature of -50°C?
Platinum - platinum + rhodium
Change of angle of refraction with composition comprises the working principle of a
refractometer
Which of the following instruments is not used for measuring sub-zero (<0°) temperatures ?
Radiation pyrometer
Which of the following is not suitable for measuring the temperature of a red hot object in the range of 800 - 1600°C ?
Thermocouples
Flame photometry is used for the determination of compositional analysis of
alkali metals
Reference points i.e., ice point and steam point in Reaumer temperature scale are respectively
0° & 80°
Emf developed by a thermocouple while measuring a temperature of 800°C is about 31 mV. The type of thermocouple used is
chromel-alumel
Which of the following is not a composition measuring instrument ?
Hot wire anemometer
Which of the following thermocouples is incapable of measuring sub-zero (i.e., < 0°C) temperature ?
Platinum-platinum + rhodium
Platinum resistance thermometer is the international standard for temperature measurement between
both (a) and (b)
0n-off control which is a special case of proportional control, has a band width of about __________ percent.
0
The thermal emf-temperature relationship of most thermocouples is
parabolic
Which is the strongest paramagnetic gas?
O2
In Bode plot, A.R. vs. w is plotted on a/an __________ graph paper.
log-lag
Dome temperature of blast furnace stove is most accurately measured by a
platinum-platinum/rhodium ther-mocuple.
Phase lag of the sinusoidal response of a first order system is
90°
Continuous measurement of moisture content of paper in paper industry is done by measuring the
electrical resistance through the paper
Thermal well made of __________ gives the fastest speed of response, while measuring temperature by thermocouples.
vycor (a glass)
For measuring the temperature of a red hot furnace, which is the most suitable instrument ?
Optical pyrometer
Continuous measurement of specific gravity of a liquid is done by
both (a) and (c)
Stroboscope is used for the measurement of
rpm of a flywheel
In second order underdamped system,
decay ratio = (overshoot)2
Pick out the wrong statement.
Transfer lag decreases as the number of stages decreases.
Working principle of mercury in glass thermometer is
volumetric expansion.
The frequency at which maximum amplitude ratio is attained is called the __________ frequency.
resonant
Conversion formula for converting amplitude ratio (AR) into decibels is
Decibel = 20 log10 (AR)
A manometer measures the __________ pressure.
gauge
Which of the following can measure temperatures in the range of - 20 to 300°C ?
None of these.
If response of a control system is to be free of offset and oscillation, the most suitable controller is
proportional integral-derivative (PID) controller.
Normal mercury thermometer can be used to measure a temperature of about 300°C. However, its maximum temperature measurement range can be increased up to about 500°C by
filling nitrogen under pressure in the stem.
Minute depression of freezing point of a liquid solvent on addition of a solid solute can be best measured by a
Beckman thermometer
Temperature of __________ can not be measured by an optical or radiation pyrometer.
hot blast (air) from stoves
Gain margin is equal to the
reciprocal of amplitude ratio
For two non-interacting first order systems connected in series, the overall transfer function is the __________ of the individual transfer functions.
product
In Bode plot, Φ vs ω is plotted on a/an __________ graph paper.
log-log
Temperature of molten pig iron (1450°C) and molten slag (1500°C) flowing out of a blast furnace is measured by a/an
either (b) or (c)
Ordinary mercury in glass thermometer is used for measuring temperature upto 120°C. However, for measuring higher temperature upto __________ °C, thermometer is made by filling nitrogen under pressure above the mercury, which stops the evaporation of mercury and reduces the chance of broken thread of mercury.
550
Mercury thermometer is commonly used for low temperature measruement. The freezing point and boiling point of mercury are respectively __________ °C.
- 39 and 350
Which of the following thermocouples has the least temperature measurement range?
Copper-constantan
