The Modal Shop, Inc. A PCB Group Co.    Global Sales   Video   Newsletters   Library   About Us  
Home > Industrial > VibeAlarm™ FAQ

VibeAlarm™ FAQ

Frequently Asked Questions

What is the basic value of the SDC002 VibeAlarm?
Well known standards are published for vibration severity levels of various classes of machinery to aid in condition health monitoring programs. In prior years it would have taken a $20,000.00 analyzer to measure these levels. Now, for well under $1000.00, the SDC002 can measure vibration severity at a price which accommodates continuous monitoring and direct connection to the process bus.

For what types of applications is the SDC002 especially well suited?

  • The SDC002 is well suited for long-term machinery-health monitoring of steady-state vibration levels (ex. pumps, fans, motors, etc.), not for detecting occasional impact events.
  • Note that the response time of the SDC002 can range from several seconds up to several minutes, depending on its configuration.
  • The adjustable band-pass filter in the SDC002 cannot be used for narrowband filtering. If the upper band edge frequency is less than about 5 times the lower band edge frequency, accuracy will be degraded by the filter roll-off near the corner frequencies.

How do power failures affect the SDC002?
The SDC002 will not operate without power, but will automatically resume normal operation as soon as power is restored. The configuration is retained without power.

Is the Peak measurement a "Calculated Peak (RMS value * 1.414)" or "True Peak?"
True Peak.

Is it possible to speed up the response time?
Yes.  For a faster response time, configure the SDC002 for:

  • Acceleration measurements rather than velocity or displacement measurements.
  • A narrower bandwidth, either by raising the lower band edge, lowering the upper band edge, or both.
  • Less accuracy.

How does the Update Rate relate to the response time of the Alert and Alarm outputs?
The response time may be limited either by the user-selectable "Time Delay", which minimizes false alarms by requiring that the condition be observed for at least the duration of the time delay, or by the measurement update rate. The minimum response time of the SDC002's Alert and Alarm outputs may be up to three times longer than the update rate.

For velocity or displacement measurements, why is the FRF plot in the Advanced Options panel flat, instead of sloped to represent integration of the accelerometer signal?
When velocity or displacement measurement is selected, the FRF plot represents the SDC002's response to a given velocity or displacement, not the response to a given acceleration.

Can the SDC002 be used for "envelope detection," or multiple frequency band monitoring?
No. But The Modal Shop’s SDC003 LanSharc with BEAR™ application firmware is well suited for these and other computationally intensive applications.

Can the design be modified to better suit my application?
Yes. When warranted by sufficient demand, we can add, subtract, or modify features of the SDC002.

Why does the band energy calculation of the VibeAlarm disagree with that of my traditional FFT analyzer?
For proper comparisons between the band energy calculations made by the VibeAlarm and those of a traditional FFT analyzer, the accelerometer signal received by both instruments must be the same (connect the FFT analyzer to the VibeAlarm's BNC output), both instruments must be configured for the same filter frequency band and the same units of measure, both instruments must be configured for RMS measurements, and the signal being measured must not have a substantial portion of its energy content near the filter band edges. The VibeAlarm and the traditional FFT analyzer will often disagree if configured for "peak," or "peak-to-peak," measurements. This is because traditional FFT analyzers compute the, "calculated peak," of the vibration, while the VibeAlarm computes the, "true peak." Calculated peak is computed by multiplying the RMS value by 1.414. True peak represents the actual peak value of the filtered, integrated time waveform. These two results should be expected to match if and only if the accelerometer signal is a pure tone sine wave. A pure tone sine wave acceleration may be generated by a PCB 394C06 Handheld Shaker, which produces a 1g RMS, 159.2 Hz sine wave acceleration. Measured with the VibeAlarm in its default 10 - 1000 Hz bandwidth, this signal may be used to compare the peak measurement of the VibeAlarm with that of a traditional FFT analyzer. A second case of disagreement occurs when a large portion of the energy content of the signal being measured lies near the edges of the bandpass filter. In this case, differences in the shape of the filter roll-off account for differences in the filter result.


Back to VibeAlarm