Long Cable Runs (Accelerometers)
Choose a conductor size that keeps the cable resistance at or below 10 Ω. This is to ensure signal accuracy and to minimize susceptibility to noise. This guideline results in the following limits to cable runs.
Long cable runs cause capacitive loading at high frequencies increasing the sensor's susceptibility to amplifier overload. A condition to be avoided is very long cables in the presence of high amplitude, high frequency signals when measuring low frequency, low amplitude signals.
The maximum permissible cable run depends on the maximum frequency of interest and the amount of current supplied to the IEPE/ICP® accelerometer. For the vbOnline device this results in the following guidelines for a typical 100 pF/m (30 pF/ft) cable.
We recommend that the sensor manufacturer reviews your measurement specifications to determine the suitability of long cable runs. If you intend to mount several sensors a considerable distance from a vbOnline device it will be more economical to install a junction box near the sensors and run a single multi-pair cable to cover the distance. This removes the need for external multiplexer boxes. Suitable junction boxes are available from most sensor manufacturers.
The multi-pair cable must have an overall shield and, ideally, should also have individual shields for each pair. Each multi-pair shield should connect to the individual sensor cable shield, but only connect to ground at the vbOnline device (not at the junction box).
Last Reviewed: 25/Mar/2011 Source: vbOnline Reference Guide Revision 11 April 2009 - pages 14 - 16