Data Collection & Instrumentation Flashcards

What is the primary advantage of an ICP® (Integrated Circuit Piezoelectric) accelerometer over a charge-mode accelerometer?

Answer: ICP sensors have built-in signal conditioning and can use long, low-cost coaxial cables without signal degradation

ICP (IEPE) accelerometers have built-in MOSFET electronics that convert high-impedance charge to low-impedance voltage output, allowing use of standard coaxial cable runs of hundreds of feet without signal quality loss.

What is the transverse sensitivity of an accelerometer?

Answer: The response of the accelerometer to vibration perpendicular to its primary measurement axis

Transverse sensitivity (typically expressed as a percentage) measures how much the accelerometer responds to motion perpendicular to its primary axis; low transverse sensitivity (< 5%) ensures measurements reflect only the intended direction.

What is the resonant frequency of an accelerometer, and why does it matter for measurements?

Answer: The frequency at which the sensor output is maximum; usable range ends well below this to avoid amplitude errors

The mounted resonant frequency of the accelerometer is its highest natural frequency; the usable frequency range is typically up to 1/3 to 1/5 of this resonant frequency to keep amplitude error below ±3–5%.

Which accelerometer mounting method typically provides the highest usable frequency range?

Answer: Threaded stud mount directly into the machine surface

A threaded stud mount directly into the machine provides the most rigid coupling, preserving the accelerometer's full mounted resonant frequency and giving the widest usable frequency range.

What is a proximity probe (eddy current sensor) primarily used for in rotating machinery instrumentation?

Answer: Measuring the relative displacement between the shaft and the bearing housing in fluid-film bearing machines

Eddy current proximity probes measure the dynamic and static gap between the probe tip and a conductive shaft, providing relative shaft displacement measurements within journal bearings as required by API 670.

What is the purpose of a low-pass anti-aliasing filter in a vibration data acquisition system?

Answer: To remove frequency components above the Nyquist frequency before analog-to-digital conversion, preventing aliasing

An anti-aliasing filter is a low-pass filter set at or below the Nyquist frequency (half the sampling rate) that removes high-frequency content before digitization, preventing those frequencies from appearing as false low-frequency aliases.