Amphenol Wilcoxon TN14 Dépannage des installations - Page 3
Parcourez en ligne ou téléchargez le pdf Dépannage des installations pour {nom_de_la_catégorie} Amphenol Wilcoxon TN14. Amphenol Wilcoxon TN14 7 pages. Accelerometer
Imprimer la pageThe BOV should be measured periodically to check sensor operation. The best measurement device is a
voltmeter, however, most portable data collectors can measure the BOV if the sensor is powered from a differ-
ent source (other than the data collector). When using the data collector as a voltmeter the DC voltage input
setting is used. Oscilloscopes can also measure the BOV by selecting the DC coupled input. The BOV can be
trended with many online systems. Trending the BOV provides a record of sensor operation. If the sensor is
disconnected or slowly develops a fault, the BOV data can show when the event occurred.
The BOV will also indicate the condition of the cabling and connectors. If the BOV level measurement is equal
to the supply voltage, the sensor may be disconnected or reverse powered. A measurement of 0 volts indicates
a short in the system. An unstable bias voltage can indicate poor connections, but can also be caused by a
clipped signal or severe electromagnetic interference.
Time waveform and FFT spectrum fault analysis
The time waveform of a sensor can be measured with an oscilloscope, most data collectors, and online vibra-
tion monitoring systems. Reviewing the time waveform can immediately indicate a clipped signal, which usually
looks truncated or flattened on one side and normal on the other. Severely clipped signals will cause the wave-
form to look jumpy. Poor connections can also cause a similar jumpy reading.
The FFT spectrum can give another quick indication of signal quality. The one-times (1X) operating speed
vibration is usually present and a good indication of proper operation. The presence of a large ski slope can
indicate distortion from sensor overload. However, a noisy accelerometer that has been integrated to velocity
or displacement may also produce ski-slopes for various reasons.
Cable routing faults can also be detected by analyzing the FFT. Multiples of the line power frequency usually
indicates improper shielding or grounding. If the time and frequency measurements read zero, the sensor is
disconnected or is not operating.
Fault indications
Open bias fault: Supply voltage (18 - 30 V)
When the measured BOV equals the supply voltage, the sensor amplifier is disconnected or reverse powered.
In most cases the problem is the connector or cabling. First check the cable termination at the junction box,
data collector or monitoring system. If the cable is connected to a terminal block, make sure the wires are
secure and in the proper terminal. Next check the cable connection to the sensor. Many times, the sensor was
disconnected for maintenance and was never reconnected. If a faulty connector is detected, it can be disas-
sembled or replaced, but avoid disassembling or removing the connector until all other fault sources have been
checked. If each end appears good, check all other terminations, splices and connectors. Also ensure that the
cable is not crushed or cut.
If the cable route and connections appear good, further test the cable continuity. Cable continuity can be tested
by shorting the signal leads at one end of the cable to the shield wire and measuring the opposite end with an
ohmmeter. Depending on the cable length, several ohms to no more than several hundred ohms should be
measured from each wire to the shield. If the cable and all connections are in proper working order, the fault is
in the sensor. However, open faults inside the sensor are very rare.
Short bias fault: 0 volts
When the bias measures 0 volts, power failure or a system short is usually the problem. First ensure that pow-
er is turned on and connected. If the power supply is on, check for a short in the cabling. Like the open fault, it
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