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PC-TDR/TDR200 "NAN" for VWC?

andrean Mar 6, 2024 01:32 AM


I am currently attempting to measure the volumetric water content of soil in large plastic containers, but the measurement summary on PC-TDR keeps returning “NAN” for EC, VWC, and permittivity.

I am using a homemade coaxial probes (120 cm cable attached to two 10.5 cm stainless steel prongs and held together with an epoxy resin) and a TDR200 reflectometer.  I am calibrating my probes and measuring VWC with PC-TDR(v.3.00.47) on a Windows 10 laptop.

First, I set up a new configuration with TDR200 as my base type, COM4 as the serial port, SDM address of 1 (same as on the physical TDR200), 50 Hz noise rejection frequency, Filter level 1, and Tangent Line Method (wintdr) as my Length Apparent Algorithm.

I then follow the steps of the calibration wizard with my coaxial cable probe.  All of the values match the dimensions of my probe and the generated figures seem similar to the ones shown on the calibration wizard in the manual, but I may be missing something.  Here are my values generated during calibration:
- Cable Length 1.7
- Window Length 3.0
- Start & End Distances in Air 2.197, 2.361
- Start & End Distances in H2O 2.191, 3.181
- Permittivity of Water 80.05 at 20.8 C
- Calibrated Probe Offset 0.0613
- Calibrated Probe Length 0.1038
- Probe Cell Constant (Kp) 76.27
- p shorted -0.9874
- p Open 0.9595

I then finish up the calibration wizard, place the probe into the pot of soil, and then refresh to take a measurement.  At this point, the program generates a waveform, but reports NAN for EC, VWC, and permittivity, as well as for the probe start and end.  If I toggle “Show Probe Start/End” under “View,” nothing in the figure changes -- there aren't the thin vertical lines indicating the start and end of the probe.

I’ve poked around in the manual and in the program but can’t seem to find any settings I’ve overlooked.  Does anyone have any ideas of what might be going wrong or of what next steps I should try?  I’ve attempted this with several of my probes and with the other algorithms, to the same result.

Thank you for your help!

Best wishes,

Andrea N

Laydi121 Mar 21, 2024 09:22 AM

This post is under review.

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