Ski Slopes: Testing Sensor Cables for Faults
QUESTION
My recordings have started showing lots of low frequency noise (ski slope) and few normal vibration peaks. Could my sensor cable be at fault?
ANSWER
Cables suffer a lot of abuse and do wear out. vbX instruments provide sensor fault detection, however a cable with an incipient intermittent fault can still slip through this test (vbX000 instruments also provide sensor fault detection, but only those with serial numbers 11500 and higher, and only on channel 1). Use the following procedure to manually test your cable.
Setting up the Measurement
vbX
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From the instrument's main menu select Measure [7] then Spectrum Waveform [6].
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Press Store Units [6] repeatedly until 'Accel' is displayed.
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Press Spectrum Waveform [7] and select a resolution of '400 lines 1024 samples'. Press the Spec Wfm [0] button until 'Waveform' is selected then the tick key.
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Press Wfm Duration [9] and choose '1 s'.
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Connect your sensor(s) and begin measuring. Once the sensor has settled and the screen is displaying the measurement, press ALT then Y Axis Fixed [2] and select 10 m/s2.
vbX000
- Place the accelerometer in a low-vibration location.
- Select the Waveform Quick Setup option and press [0] Custom Setup.
- Set the following parameters. Mode: Acceleration; Duration 1000 ms
- Now press [0] Display Options.
- Press [7] and set Acceleration Max to 10 m/s2 (1 g).
- Press [ENTER] to continue then press ^ to save your Custom Settings.
Testing the Cable
- Tap the end of the accelerometer with your finger. The instrument screen should display a trace like that shown below (this verifies that the sensor is actually working).
vbX000
vbX
- Now gently flex the cable, in particular at the end connectors and around the break-free connector. You should see small signals from the movements of the sensor.
If you see dramatic swings, as in the example below, your cable has an intermittent contact and should be replaced.
vbX000
vbX
Please also see Cleaning the BNC Connectors on the Instrument.
FAQ ID: 19037 Last Reviewed: 5 June 2009