CMRT Predictive Maintenance Technologies 3 ā Questions and Answers
Question 1: In infrared thermography, what is the primary significance of emissivity when measuring surface temperatures?
- It determines the distance at which measurements can be taken
- It affects the accuracy of the temperature reading if set incorrectly (Correct answer)
- It controls the resolution of the thermal camera
- It sets the alarm threshold for the imager
Correct answer: It affects the accuracy of the temperature reading if set incorrectly
Emissivity is the ratio of energy emitted by a surface to that of a perfect blackbody; an incorrect emissivity setting causes significant temperature measurement errors.
Question 2: During an electrical panel thermography inspection, a single-phase connection shows a temperature of 85Ā°C while the other two phases are at 35Ā°C. This most likely indicates:
- Normal load imbalance
- Loose or high-resistance connection (Correct answer)
- Overloaded circuit breaker
- Phase reversal
Correct answer: Loose or high-resistance connection
A single hot spot at one connection point with significantly elevated temperature compared to similar phases indicates a loose or corroded high-resistance connection.
Question 3: Airborne ultrasound technology detects faults primarily by sensing:
- Low-frequency vibration below 20 Hz
- High-frequency sound in the 20ā100 kHz range (Correct answer)
- Infrared radiation emitted from hot components
- Changes in magnetic flux around conductors
Correct answer: High-frequency sound in the 20ā100 kHz range
Ultrasound instruments detect high-frequency acoustic emissions (20ā100 kHz) produced by turbulent flow, arcing, or friction that are inaudible to the human ear.
Question 4: Which lubricant oil analysis test is most directly used to detect ferrous wear particles from gear or bearing surfaces?
- Viscosity measurement
- Total acid number (TAN)
- Ferrography or particle count (Correct answer)
- Flash point test
Correct answer: Ferrography or particle count
Ferrography and particle count tests quantify wear metal particles in the oil, directly indicating the rate of metallic component wear.
Question 5: In motor circuit analysis (MCA), a low megohm reading between a motor winding and ground indicates:
- An open winding
- Insulation degradation to ground (Correct answer)
- High rotor resistance
- Broken rotor bars
Correct answer: Insulation degradation to ground
Megohmmeter (Megger) testing measures insulation resistance; low values indicate moisture ingress, contamination, or physical breakdown of winding insulation to ground.
Question 6: Which condition monitoring technology is most effective for detecting compressed air or steam leaks in pressurized systems?
- Vibration analysis
- Infrared thermography
- Airborne ultrasound (Correct answer)
- Oil particle analysis
Correct answer: Airborne ultrasound
Airborne ultrasound detects the turbulent flow noise created at leak points in pressurized systems, making it highly effective for leak detection.
Question 7: The viscosity index (VI) of an oil describes:
- The oil's resistance to oxidation over time
- How much the oil's viscosity changes with temperature (Correct answer)
- The oil's ability to carry extreme pressure loads
- The concentration of additives in the oil
Correct answer: How much the oil's viscosity changes with temperature
Viscosity index is a measure of how much an oil's viscosity changes with temperature; a higher VI means the viscosity is more stable across temperature ranges.
CMRT Predictive Maintenance Technologies 3
In infrared thermography, what is the primary significance of emissivity when measuring surface temperatures?