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GATE 2026 CH – Question 12

Instrumentation and Process Control · Measurement of process variables, sensors, transducers and P&ID symbols · 1 mark · Multiple choice

In the P&ID shown below, which one of the following is the function of PAH in the process?

a gas storage tank T-101 fed by a pump P-101 and discharging through a control valve V-101 to the user. A pressure transmitter PY 101 on the tank is connected by dashed signal lines to a bubble labelled PAH 101, to a controller PIC 101 and on to PY 102 which operates the valve.
  1. to maintain a constant pressure in the vessel by throttling the pump outlet
  2. to alert when high pressure is detected in the tank
  3. to measure the average pressure in the vessel and display it locally
  4. to regulate the flow from the vessel to downstream users

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Correct answer: (B) to alert when high pressure is detected in the tank

Explanation

In P&ID tag codes the first letter gives the measured variable (P is pressure) and the later letters give the function. A is alarm and H is high, so PAH is a pressure alarm high. It warns the operator when the tank pressure goes too high. Regulating the flow is done by the controller PIC and the valve.