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Subject: Re: I'm looking for an instrument for detect cable damage

Date: 12/06/01 at 9:57 PM
Posted by: Ray
E-mail: rrogers@plaidheron.com
Message Posted:

In Reply to: I'm looking for an instrument for detect cable damage posted by Agung Irfan on 12/06/01 at 1:07 AM:

I know of three techniques.
One is called Time domain reflectometry (TDR). A pulse with a fast leading edge is sent down the cable and the time till it is reflected is measured. Unless your cable has a great deal of consistancy this will yield a lot of confusing echo's. They do sell/rent them; I think HP/AGlent made them. You probably should arrange to calibrate it with a referance cable.
Two is using a constant current into an open cable. The ramp time until the voltage ramp quits ramping indicates how long the cable is electrically.
Third is the old standby (which is probably best in your case) inject a RF signal (say 800kHz AM) into the cable and walk the cable path with a radio until the signal stops.
Actually you should be able to do this with 1kHz and a scope probe.
If your cable is in a bundle then the lower frequencies might be better to reduce pickup. The scope would be inconvient to lug around so a loop and ac voltmeter might work with a little more signal level.


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