Process Dynamics and Control Flashcards
This contains concepts and heuristics necessary for the development of process models in complex chemical engineering systems and the design of process control equipment.
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
Pick out the one which is a first order instrument.
All (a), (b) and (c).
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.
CO2is 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
Stefan-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
In a single tank system, the transfer function of level to inlet flow rate is
R/(TS+ 1)
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
Instrumentation in a plant offers the advantage of
all (a), (b) and (c)
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
CO2analyser
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
Transfer function of transportation lag is
e-TS
Temperature measuring instruments are standardised mostly with ____ points of pure substances.
both (a) & (b)
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
Which of the following controllers has the least maximum deviation ?
P-Dcontroller
Volumetric expansion is the working principle of the ____ thermometers.
mercury in glass
Which of the following measurements can be made by the measurement of emf ?
All (a), (b) & (c)
A magnetic flowmeter is
all (a), (b) and (c).
Zirconia probe is used for the continuous measurment of ____ flue gases going out of the furnace.
oxygen in
Strain gage pressure transducers are used to measure ____ pressures.
both (a) and (b)
The transfer function for a PID controller is (where, τiis the integral (reset) time and τDis the derivative time.)
Kc(1 + 1/τis+ τD * s)
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 valuesvs. 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 ofKcis used to control a first order process. The offset will increase, if
Kcis reduced.
The symbol for “capillary line” in instrumentation diagram is
0
____ is undesirable in thermocouples used in industries,
Non-linear relation of emf to temperature
Select the correct statement from the following.
The amplitude ratio of a pure capacity process is inversely proportional to frequency.
For an input forcing function,X(t) = 2t2, the Laplace transform of this function is
4/s3
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
The second order system with the transfer function (4/s2+2s+4) has a damping ratio of
0.5
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
The transfer function for an ideal proportional plus reset controller (reset time T) is
Kc (1 + 1/TS)
The frequency response of a first order system, has a phase shift with lower and upper bounds given by
0, π/2
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.
The transfer function for a P-D controller is
Kc (1 + τDs)
Bode diagram is a plot of
log (AR)vs. log (f) and (Φ) vs. log (f).
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
Pick out the wrong statement
CSTR can be considered as a distributed parameter system.
Range of hydrogen gas constant volume themometer is ____ °C.
0 to 100
The initial value (t=0) of the unit step response of the transfer function [(s + 1)/(2s + 1)] is
1/2
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).
Nitrogen gas constant volume thermometer is suitable for measuring a temperature of ____ °C.
> 100.
What is the overall transfer function (C/R) of the following block diagram if G = G1. G2. G3 and H = H1.H2.
G / (1 + GH)
Pick out the most suitable instrument for measuring temperature in the range of-40 to 425°C.
bimetallic thermometer
Accurate temperature measurement performance of a radiation pyrometer can not be affected, if the
object and surrounding are at almost the same temperature.
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
Thermodynamic celcius scale of temperature measurement is
both (b) and (c)
According to Bode stability criterian, a system is unstable, if the open loop frequency response exhibits an amplitude ratio exceeding unity at frequency for which phase lag is
180°
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.
Resistance of a gas in a vessel is given by (where,P= pressure,V= volume of the vessel,n= no. of moles of the gas,R= gas constant)
V/nRT
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
Which of the following thermocouple materials does not contain nickel ?
None of these.
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
Identify an unbounded input from inputs whose transfer functions are given below
1/S2
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
Which of the following filled system expansion thermometer has the capability to measure the lowest temperature ?
Alcohol in glass thermometer
Concentration of sugar solution can be determined by the
polarimetry
In a single tank system, the transfer function of ____ to inlet flow rate is 1/
outlet flow rate
Which of the following can not measure a temperature of 1600°C ?
Platinum resistance 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)
Transfer functionsX/Yfor which of the following block diagrams is
0
The characteristic equation for the control system with a closed loop transfer function
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/cm
differential pressure gage
Which of the systems having following transfer functions is stable?
1/(
What is the dynamic error in a critically damped second order instrument for a ramp input (At) ?
2 AT
The transfer function for a first order process with time delay is
0
An ideal PID controller has the transfer function
1/
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 unit step response of the transfer function
a monotonic increase.
A process is initially at steady state with its output y=l for an input u=l. The input is suddenly changed to 2 at time t=0. The output response is y(t)=1+2t. The transfer function of the process is
0
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
Which of the systems having the following transfer function is stable ?
0
The calibration data of a thermocouple with its cold junction at 0°C are given below.
2.46 mv
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 frequency response of a dynamic element shows a constant magnitude ratio at all frequencies. The element exhibits a negative phase shift at all frequencies. The absolute value of the phase shift increases linearly with frequency. The element has the transfer function
e
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
For the block diagram shown below :
τ
Use of
elimination of offset
Turbine flow meters are suitable for
both (b) and (c).
