Overview
In this example, an implementation of Time Domain Reflectometry (TDR) is shown. A NI Arbitrary Waveform Generator and NI Digitizer are used. The application measures the distance between the origin of the sent signal and the first impedance change in a coaxial cable (open or short termination condition).
Description
The IVI Time-domain reflectometry or TDR is a measurement technique used to determine the characteristics of electrical lines by observing reflected waveforms. Time-domain transmissometry (TDT) is an analogous technique that measures the transmitted (rather than reflected) impulse. Together, they provide a powerful means of analysing electrical or optical transmission media such as coaxial cable and optical fiber. Hardware is necessary for this application.
Requirements
Software:
- LabVIEW 2012 (or compatible)
- NI-FGEN,
- NI-SCOPE
Hardware:
- NI PXI-1042Q
- NI PXI-8196
- NI PXI-5421
- NI PXI-5142
- BNC T
- SMB112 (Double Shielded SMB to BNC Male Coax Cable)
- Coaxial Cable (at least 4 meters)
Steps to Implement or Execute Code
- Open Measurement & Automation Explorer (MAX).
- Make sure that in MAX, NI PXI-5421 is named as “Dev1”, and the NI PXI-5142 is named as “Dev 2”.
- Open the “TDR DEMO.lvproj”. Then, double click on Cable Length Meter (MAIN).vi.
- If it´s necessary, modify the Filter Parameters and/or TDR Parameters. After that, Run the application.
- Check the results. The estimated cable length is shown. In addition, other results are included. The TDR ORIGINAL SIGNAL tab presents the raw signal in the coaxial cable. The TDR FILTERED SIGNAL tab shows this signal after a band pass filter is applied. Finally, the TDR NON NEGATIVE SIGNAL tab presents two parabolas used to estimate the distance to the cable termination (or cable length).
Additional Information or References
VI Snippet
**This document has been updated to meet the current required format for the NI Code Exchange.**