My user want to use TDR100 for Rock Mass deformation application, the expect distance is 1500m. I am worried about cable length, What is the maximum length of TDR100 using the RG8 cable?
I noticed the specification of TDR100 as follow:
distance(Vp=1) time(1 way travel)
range : -2 to 2100m 0 to 7us
resolution: 1.8mm 6.1ps
If we change the VP to 0.78, how about the range, how to calculate?
If use multiplexer to observe two cable, how about each cable range?
the manual talks about a length of over 2000m.
but it also talks about minimizing cable loss by using low loss cable. you might consider using an even lower loss cable than rg8 - like lmr400 or better.
but i suggest you give the soils group at csi a call
Best to speak to an expert (not me), but to clarify a few points.
1) The maximum distances for this type of application is ultimately limited by the "time base" limit of 7 microsecs.
2) For a cable with a lower Vp than 1 then the maximum distance will come down proportionally. 1500m will be close to the limit with that cable.
3) the distance resolution again is proportional to Vp, but is the absolute maximum resolution if you select to capture a trace from a short length of cable. The maximum number of points you can capture in one go is 2048 points. If you tried to sample the entire trace for a 2000 m cable, in one go, the resolution would only be 1 metre. You can capture at higher resolution for long cables by measuring the cable in a stepwise fashion.
4) Sam mentions that you need to select the cable carefully. This is more of a problem for soil moisture measurements, but also applies to mass deformation use as you can loose sensitivity to the start of deformation if you use a higher loss cable for long distances.