CMRT Predictive Maintenance Technologies Questions and Answers

Question 1

A vibration analyst observes a predominant spectral peak at two times (2x) the running speed on a direct-coupled pump and motor. This is a classic indicator of which of the following mechanical faults?

Accepted Answer

Angular misalignment

Answer

A strong vibration signal at twice the running speed (2x) is a primary indicator of angular misalignment between coupled shafts. Imbalance typically shows at 1x, bearing faults have their own specific non-harmonic frequencies, and looseness often presents as multiple harmonics (1x, 2x, 3x, etc.).

Question 2

While performing an infrared scan on an energized Motor Control Center (MCC) panel, a technician identifies a circuit breaker's terminal lug that is significantly hotter than adjacent ones under similar load. What is the most probable cause of this thermal anomaly?

Accepted Answer

High electrical resistance

Answer

Heat is generated when current flows through resistance (P=I²R). A loose, corroded, or improperly crimped connection creates high resistance, which manifests as a localized hot spot under electrical load. Since adjacent components under similar load are not hot, it rules out motor load or ambient temperature as the primary cause.

Question 3

A technician is using an ultrasonic sensor to perform condition-based lubrication on a motor bearing. What is the primary indicator that the correct amount of grease has been applied?

Accepted Answer

The decibel (dB) level of the bearing drops to a normal baseline.

Answer

Ultrasonic instruments detect the high-frequency sounds of friction within a bearing. As the correct amount of grease is applied, it lubricates the components, reducing friction and the associated sound. The technician listens for the decibel (dB) level to drop to a pre-determined baseline for a healthy bearing. Over-greasing can cause the dB level to rise again due to churning.

Question 4

An oil analysis report for a large hydraulic system shows a high particle count, an elevated silicon (Si) level, and a noticeable increase in oil viscosity. Which of the following is the most likely root cause?

Accepted Answer

Ingress of dirt and dust from the environment

Answer

Silicon (Si) is the primary elemental indicator of dirt/sand ingress, often from a faulty breather or seal. This external contamination is abrasive, which explains the high particle count from accelerated wear. Dirt particles can also cause the oil to thicken, leading to an increase in viscosity.

Question 5

Which of the following predictive technologies is most effective for detecting broken or cracked rotor bars in an AC induction motor while the motor is in operation?

Accepted Answer

Motor Current Signature Analysis (MCSA)

Answer

Motor Current Signature Analysis (MCSA), a form of Motor Circuit Analysis, analyzes the motor's current draw. Broken rotor bars create distinct sideband frequencies around the main 60 Hz (or 50 Hz) line frequency peak in the current spectrum, allowing for early and accurate detection while the motor is running under load.

(CMRT) Certified Maintenance and Reliability Technician Practice Test

(CMRT) Certified Maintenance and Reliability Technician Practice Test

CMRT Predictive Maintenance Technologies Questions and Answers