Instrumentation and Process Control Flashcards
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what is the laplace transform of sin t?
1/s^2+1
The transfer function of the first order system is
1/Ts+1
Pick out the first order system from among the following
mercury in glass thermometer kept in boiling water
Response of a system to a sinusoidal input called
frequency response
What is the ratio of output amplitude to input amplitude for a sinusoidal forcing function in a first order system?
none of these
(a) 1
(c) < 1
(b) > 1
Phase lag of the sinusoidal response of a first order system is
120 degree
Conversion formula for converting amplitude ratio (AR) into decibels is
Decibel=20 log10 (AR)
“A control system is unstable if the open loop frequency response exhibits an amplitude ratio exceeding unity at the cross-over frequency.” This is
Bode stability criterion
Typical specifications for design stipulates the gain margin and phase margin to be respectively
> 1.7 and > 30°
The frequency at which maximum amplitude ratio is attained is called
resonant frequency
A negative gain margin expressed in decibels means
unstable system
Bode diagram is a plot of
log (AR) vs. log (f) and Ø vs. log (1)
For measuring the temperature of a furnace, which is the most suitable instrument?
Optical pyrometer
Degree to which an instrument indicates the changes in measured variable without dynamic error is called
fidelity
Which of the following is a desirable characteristic of an instrument?
high fidelity
Which of the following shows maximum dip affect
(indicating reverse direction of temperature change)?
mercury thermometer
Pick out the most suitable instrument for measuring temperature in the range of -40 to 800°F.
bimetallic thermometer
Thermocouple is suitable for measuring
both high and low temperature
Which of the following relates the absorption and evolution of heat at the junctions of a thermocouple to the current flow in the circuit?
Peltier effect
Thermal wells are used in temperature measurement to
guard against corrosive and oxidizing action on thermocouple materials
Gas analysis is commonly done using
thermal conductivity cell
Psychrometer determines
humidity of gases
Continuous measurement of moisture done by measuring
electrical resistance through the paper
Optimal activity of a solution can be determined using a
polarimeter
A simple pitot tube measures
Static pressure
Pirani gauge also known as thermal conductivity gauges is used for
measurement of high vacuum
A barometer measures
absolute pressure
The level of a liquid under pressure can be determined using
Differential pressure manometer
Continuous measurement of specific gravity of a liquid is done by
Hydrometer and displacement meter
Hot wire anemometer is used for the measurement of
flow rates of fluid
Flow rate through an orifice is
proportional to the square root of pressure
Which of the following flow-metering instruments is an area meter?
rotameter
Continuous measurement of flow rates of dry granular fertilizer is done using
weighing meters
Pick out the symbol for “locally mounted instrument” in instrumentation diagram
O
Which is the symbol for “pneumatic control valve”
The symbol for “capillary line” in instrumentation diagram is
Instrumentation in a plant offers the advantage of
greater safety of operation
better quality of product
greater operation economy
Dilatometer is used to measure
contraction/expansion due to changes
Stalagmometer is used for the measurement of
surface tension
Stroboscope is used for the measurement of
rpm of a flywheel
Minute depression of freezing point of a liquid solvent or addition of a solid solute
Beckman thermometer
Gain margin is equal to the
Reciprocal of amplitude ratio
Phase margin is equal to
180° - phase lag
A system with a transfer function 2s is of 4s+1
1st order
Bode stability method uses
open loop transfer function
Routh stability method uses
closed loop transfer function
Nichel’s chart deals with
closed loop values vs. open loop value
The fluid used in hydraulic controller is
oil
Number of poles in a system with transfer function 1/s^2 + 2s^2 + 1 is
3
Which of the following controllers has maximum offset?
P-controller
Process degrees of freedom
indicates the maximum number of controllers to be used
Resistance of a gas in a vessel is
V/NRT
In an exothermic chemical reactor, the manipulated variable is the flow rate of
coolant
Which of the following error integral is considered as the best criterion in controller settings?
Integral from 0 to infinity | e |dt
Cascade control means
more than one feed-back loop
Which of the following controllers has the least maximum deviation?
P-D controller
Measurement of pressure in ammonia reactor is done by
Bourdon gauge
Pressure of 0.01 psi (absolute) can be measured by
Mcleoid gauge
Continuous measurement of moisture in paper is done by
high resistance
Wheatstone’s bridge circuit (strain gauge)
Pressure of 0.0001 absolute psi can be measured by
Meloid gauge
E.m.f. generated by thermocouples is of the order of
millivolts
Measurement of sub-zero Celsius temperature in industry is done by
resistance thermometers
Starting temperature of optical radiation pyrometer is
800°C
Which thermocouple can be used to measure temperature around 1400°C?
platinum-platinum+rhodium
pH meter has
Two cells
Maximum differential pressure in liquid manometer is
30psi
Interfacial level in pressure vessel is measured by
manometers of float type
Flow rate of sludge is measured by
Kennison nozzle
Composition of natural gas can be determined by
chromatograph
Bellows are made of
Thin copper
Flapper nozzle is a
pneumatic controller
Weir valve is used for
slurries
Valve used to supply oil to burner is
rotary plug valve
Mode used for transmitting signal for one kilometer distance is
electronic
Use of pilot in transmission (pneumatic) is to
Change the flow of air
Final control element is a
valve
Example of a second order instrument is a
mercury-glass thermometer with covering
does not vary with time
Offset
Regulator problem means that
set point is constant
Servo problem means that
load is constant
Critically damped system means that the damping coefficient is
1
In Bode stability criterion, amplitude ratio at 180° should be
< 1
Phase plane method is used for
nonlinear-behavior
Laplace transform method is used for
linear behavior
Phase lag of first order system is
tan^-1 (w T)
P-I controller as compared to P-controller has a
higher maximum deviation
longer period of oscillation
longer response time
Difference at any instant between the value of controlled variable and the set point is called
deviation
The time difference by which the output of a P-D controller leads the input when theinput changes linearly with time is called
derivative time
Steady state deviation resulting from a change in the value of the load variable is called
offset
Time required for the output of a first order system to change from a given value to within 36.8% of the final value when a step change of input is made is called
time constant
A controller action in which there is a continuous linear relation between value of the controlled variable and rate of change of controlled output signal is called
integral action
A controller action in which there is a continuous relation between value of the controlled variable and the value of the output signal of the controller is called
Proportional action
Steady state ratio of the change of proportional controller output variable and the change in actuating signal is called
proportional sensitivity
In case of flow measurement by an orifice, the pressure difference signal is proportional to
Q^2
Thermistor is a
semiconductor whose resistance decreases with temperature rise
Which of the following factors does not influence measurement accuracy?
(none) : static and dynamic error, dead zone and reproducibility
Which of the following is suitable for measuring the temperature of a red hot moving object (e.g. steel ingots on roller table)?
radiation pyrometer
need cold junction compensation
Thermocouples
Selection of material for thermocouple depends on the
minimum and maximum temperature
Radiation pyrometers
none of these :
(a) have very low speed of response
(b) need not “see” the temperature source; it is measuring
(c) can’t measure temperature of objects without making physical contact
V-notch is used to measure flow rate of a liquid in
an open channel
Which of the following is not a head flowmeter?
rotameter
Use of I-control along with P-control facilitates
elimination of offset
Flow rate of a liquid containing heavy solids (e.g. sand) can be best measured by
eccentric orifice
has poor accuracy on high orifice ratios (above 0.75)
Orifice plates for flow measurement
Pitot tube is used
line is large
velocity is high
In an area meter (e.g. rotameter), the flow rate is
inferred from the change in area of an orifice in the flow line across which the pressure differential is constant zero
incurs constant and small permanent pressure drop
A rotameter
is a two position (fully open or fully closed) control adequate to control a process with slow reaction rate and minimum dead time or transfer lag
On-off control
moves the final control element at constant speed in either direction in response to an error signal
Floating control action
All:
(a) the continuous adjustment of the set point index of an automatic control loop by a primary (master) controller
(b) used when changes in process conditions cause serious upsets
in controlled variable
(c) useful to control flow from temperature
Cascade control
