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