We have a job where the analyser is a long way away from the analyser powered 100mv/g accelerometer. Using RG58 coax cable does anyone know the maximum cable length before signal problems?

Thanks in advance. John

Pending the resistance drop in the cable you may need a external xducer supply that provide higher constant current supply like 4 or 8 mA or more to make sure the xducer amplifer get voltage supply enough to operate. Check manufacturer they normally have chart for supply current versus cable length for their xducers. Olov

You may want to use an external power supply but and if you have a good setup basically you can drive a 1000' of cable from pwr supply to transducer and 50' from pwr supply to RTA as a basic rule. As Olov suggest; do it per your setup and ensure it's adequate else change to something that is adequate.

I think some data collectors only recommend ~15' from box to transducer if you're using the internal pwr supply but don't take this as fact and check your system.

The current supplied and the capacitance of the cable are the limiting factors. IF the data collector supplies 4 - 5 mA, several hundred feet of cable shouldn't be a problem. If insufficient current is supplied, the "slew rate" is limited, resulting in some hgih frequency roll-off and rounding of square waves.

If you need to go more than a few hundred feet, knowing the supply current, cable capacitance and accelerometer specs will allow some calculations to be made.

Jon
jon@spintelligentlabs.com

IMI has a technical note regarding long cables available at:

http://www.imi-sensors.com/technical/driving.asp


RG-58 cable has a capacitance of about 30 pF/ft.

Based on the above, with a 2 mA ICP supply current , and a 10 kHz maximum signal at 70 g peak (the maximum level for a 100 mV/g accelerometer), you could drive around 700 feet of cable with no deterioration in the signal.

Impacting/impulsive signals would show some rounding of the waveform at this level and length.

A couple hundred feet of cable should be no sweat for any data collector.

One caution.....if you join lengths of cables using "bullets"....keep them insulated from each other and from any metal objects. Also avoid running cables parallel to high voltage or high current cables. Strapping them to the power cable seems convenient, but is a really bad idea.

Jon
Spintelligent Labs

Thanks very much, most helpful. I will only be looking at low frequency so it looks like the 60 metres of cable should be fine.
Cheers, John