ITMC Instrumentation & Measurement 2 — Questions and Answers
Question 1: What is the purpose of instrument calibration?
- To clean and lubricate the sensing element of a field instrument
- To verify and adjust an instrument's output to match a known traceable standard (Correct answer)
- To replace worn sensing components with factory-new parts
- To document an instrument's historical failure modes
Correct answer: To verify and adjust an instrument's output to match a known traceable standard
Calibration verifies that an instrument's output accurately matches a known traceable reference standard and makes corrections as needed to ensure measurement accuracy.
Question 2: Which device converts a non-electrical physical quantity such as pressure or temperature into a standardized electrical signal?
- Actuator
- Relay
- Transducer (Correct answer)
- Controller
Correct answer: Transducer
A transducer converts one form of energy or physical quantity into another, most commonly converting process variables like pressure, temperature, or flow into electrical signals.
Question 3: What physical principle does an orifice plate use to infer fluid flow rate?
- Doppler frequency shift of ultrasonic waves
- Bernoulli's principle relating velocity to differential pressure (Correct answer)
- Coriolis effect on a vibrating flow tube
- Electromagnetic induction in a conductive fluid
Correct answer: Bernoulli's principle relating velocity to differential pressure
Per Bernoulli's principle, fluid velocity increases and static pressure decreases as it passes through the orifice restriction, creating a differential pressure proportional to flow rate.
Question 4: What type of thermometer measures temperature by detecting the infrared energy emitted by an object?
- Bimetallic thermometer
- RTD probe thermometer
- Infrared pyrometer thermometer (Correct answer)
- Filled-system thermometer
Correct answer: Infrared pyrometer thermometer
An infrared pyrometer measures temperature by detecting the infrared radiation emitted by an object, enabling non-contact temperature measurement of moving or hazardous targets.
Question 5: In process instrumentation, what does the term 'span' refer to?
- The time required for an instrument to respond to a step change in input
- The arithmetic difference between the upper and lower range limits of the instrument (Correct answer)
- The accuracy of the instrument at the midpoint of its range
- The maximum cable length allowed between sensor and transmitter
Correct answer: The arithmetic difference between the upper and lower range limits of the instrument
Span is the difference between the upper range value and the lower range value, representing the total measurement range the instrument is configured to cover.
Question 6: What is the function of a control valve as the final control element in a process loop?
- To measure and transmit the process variable to the controller
- To manipulate fluid flow in response to the controller's output signal (Correct answer)
- To supply electrical power to the sensing instruments in the field
- To display the current process variable value to the operator
Correct answer: To manipulate fluid flow in response to the controller's output signal
The control valve is the final control element that physically manipulates process fluid flow in response to the controller signal, bringing the process variable to the desired setpoint.
Question 7: What is the standard pneumatic signal range used in industrial process instrumentation?
- 0–10 PSI
- 3–15 PSI (Correct answer)
- 0–20 PSI
- 5–25 PSI
Correct answer: 3–15 PSI
The standard pneumatic control signal range is 3–15 PSI, where 3 PSI represents 0% of span and 15 PSI represents 100%; the live-zero at 3 PSI allows detection of a broken or disconnected signal line.
ITMC Instrumentation & Measurement 2
What is the purpose of instrument calibration?