Chemical Engineering
GATE CH topic:instrumentation-and-process-control PYQs
Build your understanding with focused practice from past exam papers.
Questions 11–20 of 54. Imported answers require independent review unless marked reviewed.
Question 23
Open questionCHMCQ1 markNeeds review
Consider the control structure for the overhead section of a distillation column shown in the figure. The composition controller (CC) controls the heavy key impurity in the distillate by adjusting the setpoint of the reflux flow controller in a cascade arrangement. The sign of the controller gain for the pressure controller (PC) and that for the composition controller (CC) are, respectively,
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Open questionCHMCQ2 marksNeeds review
For the block diagram shown in the figure, the correct expression for the transfer function
is 
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Open questionCHNAT2 marksNeeds review
Consider the surge drum in the figure. Initially the system is at steady-state with a hold-up
, which is 50% of full tank capacity,
, and volumetric flow rates
. The high hold-up alarm limit
while the low hold-up alarm limit
. A proportional (P-only) controller manipulates the outflow to regulate the hold-up
as
. At
,
increases as a step from
to
. Assume linear control valves and instantaneous valve dynamics. Let
be the minimum controller gain that ensures
never exceeds
. The value of
, in
, rounded off to 2 decimal places, is ________ 
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 64
Open questionCHNAT2 marksNeeds review
A PD controller with transfer function
is used to stabilize an open-loop unstable process with transfer function
, where
and time is in minutes. From the necessary conditions for closed-loop stability, the maximum feasible value of
, in minutes, rounded off to 1 decimal place, is __________Log in to check the answer
You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 25
Open questionCHMCQ1 markNeeds review
A liquid surge tank has
and
as the inlet and outlet flow rates respectively, as shown in the figure below.
is proportional to the square root of the liquid level
. The cross-sectional area of the tank is 20 cm². Density of the liquid is constant everywhere in the system. At steady state,
cm³s⁻¹ and
cm. The variation of
with
is approximated as a first order transfer function. Which one of the following is the CORRECT value of the time constant (in seconds) of this system? 
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 44
Open questionCHMCQ2 marksNeeds review
A cascade control strategy is shown in the figure below. The transfer function between the output (
) and the secondary disturbance (
) is defined as
Which one of the following is the CORRECT expression for the transfer function
? 
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 45
Open questionCHMCQ2 marksNeeds review
Level (
) in a steam boiler is controlled by manipulating the flow rate (
) of the make-up (fresh) water using a proportional (P) controller. The transfer function between the output and the manipulated input is
. The measurement and valve transfer functions are both equal to 1. A process engineer wants to tune the controller so that the closed-loop response gives decaying oscillations under servo mode. Which one of the following is the CORRECT value of the controller gain to be used by the engineer?Your answerChoose one option.
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 61
Open questionCHNAT2 marksNeeds review
The outlet concentration
of a plug flow reactor (PFR) is controlled by manipulating the inlet concentration
. The following transfer function describes the dynamics of this PFR.
In the above equation,
m
,
m
min
and
min
. The measurement and valve transfer functions are both equal to 1. The ultimate gain, defined as the proportional controller gain that produces sustained oscillations, for this system is _____ (rounded off to one decimal place).Log in to check the answer
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Open questionCHNAT2 marksNeeds review
The transfer function of a measuring instrument is
At time
, a step change of +1 unit is introduced in the input of this instrument. The time taken by the instrument to show an increase of 1 unit in its output is _____ (rounded off to two decimal places).Log in to check the answer
You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 21
Open questionCHMCQ1 markNeeds review
A control system on the jacket side of a reactor is shown in the figure. Pressurized water flows through the jacket to cool the reactor. The heated water flashes in the boiler. The exothermic reaction heat thus generates steam. Fresh boiler feed water (BFW) is added to make-up for the loss of water as steam. Assume that all control valves are air-to-open. The controller action, ‘direct’ or ‘reverse’, is defined with respect to the controller. Select the option that correctly specifies the action of the controllers.
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