Subtopic: Fundamentals of Biomolecules, enzyme kinetics
Question Statement:
The process and instrumentation diagram for a feedback control strategy to
maintain the level (h) of a liquid by regulating a valve (V) in a tank is shown
below. F, is inlet liquid flow rate, F, is outlet liquid flow rate, LT is the liquid
level transmitter, LC is the liquid level controller, hs is the setpoint value of
the liquid level, his the measured value of the liquid level and P, is the valve
pressure.
F,
LT
(LC
_h
Sp
h
F,
The manipulating variables) is/are
Options:
(A) F, only
(B) F, only
(C) hm and P, only
(D) hs and P, only
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2021 Q.23)**
**1. Governing Concept**:
- **Topic**: Process Dynamics & Control (Feedback Control Loops)
- In a feedback liquid level control loop:
- Controlled variable: Liquid level $h$.
- Measured variable: $h_m$ (via level transmitter LT).
- Setpoint: $h_{sp}$.
- Manipulated variable: The variable adjusted by the controller/actuator to maintain the level at setpoint. The control valve $V$ is installed on the inlet line to modulate the **inlet liquid flow rate $F_1$** (or outlet flow rate $F_2$, whichever line contains the control valve).
- In the schematic, the control valve regulates flow rate $F_1$.
**2. Option Analysis**:
- **Option (A) [F1 only] is CORRECT**: The manipulated variable directly actuated by the control valve.
- **Option (B) is INCORRECT**: Unmanipulated flow rate.
- **Option (C) is INCORRECT**: $h_m$ is the measured variable, $P_v$ is the controller output signal.
- **Option (D) is INCORRECT**: $h_s$ is the setpoint.
**3. Final Answer**:
- **Correct Choice**: **A**
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