TDR Metters

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ITO

Senior Member
Location
Texas
I have a remediation job in big lab, with VERY small windows of time the lab can be down. The problem is I am replacing all the feeders including the emergency power feeders and I do not have exact wire measurements. (In a nutshell the insulation on the old feeders is failing)

The plan is to use a TDR meter to measure the feeders a week ahead of time, then get my wire cuts in the Southwire, no-lube, with color insulation. Yeah I am trying to save time ANY way I can.

Here is my question: Does ayone have any experience with TDR meters? Specifically I am looking at the Megger TDR-900 which is good to withing 20".

Any comments welcome.
 
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Power Tech

Senior Member
Location
Lebec, California
ITO said:
I have a remediation job in big lab, with VERY small windows of time the lab can be down. The problem is I am replacing all the feeders including the emergency power feeders and I do not have exact wire measurements. (In a nutshell the insulation on the old feeders is failing)

The plan is to use a TDR meter to measure the feeders a week ahead of time, then get my wire cuts in the Southwire, no-lube, with color insulation. Yeah I am trying to save time ANY way I can.

Here is my question: Does ayone have any experience with TDR meters? Specifically I am looking at the Megger TDR-900 which is good to withing 20".

Any comments welcome.
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Looked at them. Want one. That's my experience with them. Think you have a good idea if the job will pay for it.
 
ELA

ELA

Senior Member
Occupation
Electrical Test Engineer
I have used TDRs on LAN and coax cables but not on individual conductors. How accurate do you want your estimate to be?

Be careful to read the specifications. The meter you mentioned has a resolution of 20".
Its accuracy is +/- 2% of reading + 20" when the cable length is less than 300ft.

You also must set the cable impedance and Velocity factor correctly in order to get accurate readings.

It is helpful if you have a test piece -of the cable of known length- that you then can calibrate the meter to in advance.
 
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dbuckley

Senior Member
Location
Canterbury, New Zealand
Used these a lot back in the day with coax 10neg ethernet.

I think the problem you'll face is that you have non-constant impedence and probably non constant velocity, as the cables are not mechanically "structured" like coax or twisted pair is. So yeah, I'd definitely want to try it first in a non-time-critical environment!
 
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