PO Instrumentation & Measurement 1 — Questions and Answers
Question 1: What does a differential pressure transmitter measure?
- The difference in pressure between two points in a system (Correct answer)
- The absolute pressure at a single measurement point
- The temperature of a fluid using pressure correlation
- The flow velocity at the pipe centerline
Correct answer: The difference in pressure between two points in a system
A differential pressure transmitter measures the pressure difference between two points, which is commonly used to infer flow rate, level, or filter condition.
Question 2: Which type of flowmeter uses the principle of electromagnetic induction to measure the flow of conductive fluids?
- Turbine flowmeter
- Magnetic flowmeter (Correct answer)
- Vortex flowmeter
- Coriolis flowmeter
Correct answer: Magnetic flowmeter
Magnetic flowmeters apply Faraday's law of electromagnetic induction — a conductive fluid moving through a magnetic field generates a voltage proportional to the flow velocity.
Question 3: What is the primary purpose of a thermowell installed in a process pipe or vessel?
- To amplify the temperature signal before transmission to the control room
- To protect the temperature sensor from direct contact with the process fluid (Correct answer)
- To convert temperature directly into a 4-20 mA signal
- To compensate for ambient temperature variations around the instrument
Correct answer: To protect the temperature sensor from direct contact with the process fluid
A thermowell is a closed-end tube that shields the temperature sensor from corrosive, high-pressure, or high-velocity process fluid while still allowing accurate heat transfer for measurement.
Question 4: A pressure gauge reads 50 psig. If local atmospheric pressure is 14.7 psia, what is the absolute pressure?
- 35.3 psia
- 50.0 psia
- 64.7 psia (Correct answer)
- 100.0 psia
Correct answer: 64.7 psia
Absolute pressure equals gauge pressure plus atmospheric pressure: 50 psig + 14.7 psia = 64.7 psia.
Question 5: Which instrument detects whether liquid is present or absent at a specific elevation inside a vessel?
- Pressure transmitter
- Level switch (Correct answer)
- Flow totalizer
- Density meter
Correct answer: Level switch
A level switch provides a discrete (on/off) output signal when liquid reaches or drops below a set point, triggering alarms or shutdown actions.
Question 6: What does PID stand for in the context of a process controller?
- Process Integral Distribution
- Proportional-Integral-Derivative (Correct answer)
- Pressure-Indicator-Display
- Process Input Data
Correct answer: Proportional-Integral-Derivative
PID stands for Proportional-Integral-Derivative — the three mathematical control actions applied to the error signal to calculate the controller output and minimize process deviation.
Question 7: An orifice plate installed in a process pipeline creates a measurable pressure drop used to determine which variable?
- Temperature
- Liquid level
- Fluid density
- Flow rate (Correct answer)
Correct answer: Flow rate
An orifice plate restricts flow and creates a differential pressure proportional to flow rate squared; higher flow produces a greater pressure drop, per Bernoulli's equation.
PO Instrumentation & Measurement 1
What does a differential pressure transmitter measure?