Condition Monitoring & Diagnostics Flashcards

When no OEM limits exist, a common way to set statistical alarm levels for a machine group is:

Answer: Use the baseline mean plus a multiple of the standard deviation (e.g., +2 to +3 sigma)

Statistical alarms use the population mean plus 2-3 standard deviations to flag abnormal readings.

ISO 10816-3 / 20816-3 severity zones for industrial machines are primarily based on which measurement?

Answer: Broadband velocity RMS, typically 10-1000 Hz

These standards evaluate broadband RMS velocity measured on non-rotating parts, typically 10-1000 Hz.

What do non-contact proximity probes on a fluid-film bearing machine measure?

Answer: Relative displacement of the shaft with respect to the bearing housing

Eddy-current proximity probes measure shaft motion relative to where the probe is mounted.

An orbit plot that looks banana-shaped or figure-8 most often suggests which condition?

Answer: High preload such as misalignment

Misalignment preload constrains the shaft, flattening the orbit into banana or figure-8 shapes with 2x content.

Which accelerometer mounting method provides the widest usable frequency response?

Answer: Stud mount on a flat, spot-faced surface

Stud mounting gives the highest mounted resonance and therefore the widest usable frequency range.

With an Fmax of 1,000 Hz and 800 lines, what is the spectral resolution (bin width)?

Answer: 1.25 Hz

Resolution = Fmax / lines = 1,000 / 800 = 1.25 Hz.

Why can trending overall velocity alone miss early rolling-element bearing defects?

Answer: Early bearing defects produce low-amplitude, high-frequency energy that barely changes overall velocity

Early defect energy is small and high-frequency, so it is masked by larger low-frequency components in the overall value.