This product is no longer available and has been replaced by: TDR200. Some accessories, replacement parts, or services may still be available.
TDR100 Time-Domain Reflectometer
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The TDR100 Time-Domain Reflectometer is the core of the Campbell Scientific time-domain reflectometry system. This system is used to accurately determine soil volumetric water content, soil bulk electrical conductivity, rock mass deformation, or user-specific time-domain measurement. Up to 16 TDR100s can be controlled using a single Campbell Scientific datalogger. PC-TDR software is used with our TDR100-based systems during system setup and troubleshooting. It can be downloaded from the Downloads section of the web page.

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Benefits and Features

  • Compact, low-cost reflectometer
  • Designed for use in remote applications
  • Determines volumetric water content and electrical conductivity in soil and other porous media
  • Compatible with CR800, CR850, CR1000, and CR3000 dataloggers


Technical Description

The TDR100 (1) generates a short rise time electromagnetic pulse that is applied to a coaxial system that includes a TDR probe for soil water measurements and (2) samples and digitizes the resulting reflection waveform for analysis or storage.

The elapsed travel time and pulse reflection amplitude contain information used by the on-board processor to quickly and accurately determine soil volumetric water content, soil bulk electrical conductivity, rock mass deformation or user-specific, time-domain measurement.

The data logger collects a 250-point waveform and analyzes it in approximately two seconds. Each waveform can have up to 2,048 data points for monitoring long cable lengths used in rock mass deformation or slope stability. Averaging up to 128 readings makes accurate measurements possible in noisy environments.


Pulse Generator Output 250 mV into 50 Ω
Output Impedance 50 Ω ±1%
Time Response of Combined Pulse Generator & Sampling Circuit ≤ 300 ps
Pulse Length 14 µs
Timing Resolution 12.2 ps
Waveform Averaging 1 to 128
Electrostatic Discharge Protection Internal clamping
Power Supply Unregulated 12 V (9.6 to 16 V)
300 mA maximum
Operating Temperature Range -40° to +55°C
Pulse Generator Aberrations
  • ±5% (within first 10 ns)
  • ±0.5% (after 10 ns)
Dimensions 23.6 x 5.9 x 12.6 cm (9.3 x 2.3 x 5.0 in.)
Weight 726 g (1.6 lb)

Waveform Sampling

-NOTE- 20 to 2048 waveform values over chosen length

Distance is Vp=1. Time is one-way travel.
  • -2 to 2100 m (distance)
  • 0 to 7 µs (time)
  • 1.8 mm (distance)
  • 6.1 ps (time)

Current Drain

During Measurement 270 mA
Sleep Mode 20 mA
Standby Mode 2 mA


Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.


Product Compatible Note
CR1000 (retired)
CR200X (retired)
CR216X (retired)
CR5000 (retired)
CR800 (retired)
CR850 (retired)
CR9000X (retired)

Mounting Equipment

Product Compatible Note

Additional Compatibility Information

Data Logger Considerations

To control the TDR100, the data logger uses TDR100 instruction in CRBasic or Instruction 119 in Edlog. All CR800-series, CR1000, and CR3000 operating systems (OS) are compatible with the TDR100. The CR10X operating system (OS) should be version 1 rev. 13 or higher and the CR23X OS should be version 1 rev. 10 or higher.

Enclosure Considerations

The TDR100 requires a desiccated, non-condensing environment; a Campbell Scientific enclosure is recommended. The TDR100's case has mounting flanges for attachment to the 1 in.-on-center hole grid of Campbell Scientific enclosures.


TDR100 OS v.0.9724 (60 KB) 15-08-2012

Current TDR100 Operating System. PC-TDR must be connected to TDR100.

PC-TDR v.3.0 (7.34 MB) 15-12-2016

Support software designed for the TDR200 and is also compatible with the retired TDR100 Time-Domain Reflectometer.

View Revision History

FAQs for

Number of FAQs related to TDR100: 19

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  1. Theoretically, yes, this can be done. However, it is more common to use a second data logger both for resilience reasons and because there are advantages in keeping TDR cables short. It is best to distribute the systems across the test site rather than trying to centralize everything.

  2. These three multiplexers all use the same relay board, but the housing differs. The multiplexers are described side-by-side on page 2 of this brochure.

    The most popular model is the SDMX50SP, followed by the SDMX50.

  3. Campbell Scientific offers six soil probes that have different rods and connector cables, allowing them to be used in diverse soil types and with a variety of cable lengths. For more details, see the listed TDR100 probes.

  4. Yes. The data logger can be programmed to store time-series data from the TDR100. The time-series data can then be viewed using PC400 or LoggerNet. For program examples, see the TDR100 Instruction Manual.

  5. The TDR100 ships with the items listed in the Ships With box on the right side of this page.

    In addition, consider purchasing the ENCTDR100 TDR System Enclosure. This enclosure ships with many items necessary for a TDR100 Data Acquisition System. See the Ships With box on the right side of this page.

  6. Slope stability/rock mass deformation instrumentation is used to detect slope movement and rock mass deformation associated with landslide, mining, and construction activities. In many applications, the ground movement readings are processed by a data logger.

    Application engineers at Campbell Scientific can provide a list of geotechnical system integrators who can offer guidance and/or support for TDR cable selection, installation, waveform interpretation, and alarm condition set points.

  7. To understand the readings obtained from a data logger program, it is necessary to see how the TDR100 operates in PC-TDR. Either the TDR100 commands are entered in PC-TDR and the user waits to see the results, or the data logger sends the TDR100 commands and automatically stores the results.

    Campbell Scientific suggests initially entering the TDR100 commands in PC-TDR and waiting for the results before writing a data logger program. This allows verification that the TDR100 is operating correctly in PC-TDR. After that has been verified, a data logger program can be created for the TDR100 that sends the commands and stores the results.

  8. Yes. PC-TDR can send control commands to advance through the channels of a SDMX50-series multiplexer. To do this, select Settings | Multiplexer and then add the multiplexers and probes that match the TDR100 system.

  9. No, as of September 2014. The PC-TDR support software can be downloaded free-of-charge from the Downloads section of the PC-TDR product page.

Case Studies

Illinois: Automating a Data System
The McCook Reservoir is a ten-billion-gallon reservoir located in La Grange, Illinois. The Metropolitan more
Illinois: Automating a Data System
The McCook Reservoir is a ten-billion-gallon reservoir located in La Grange, Illinois. The Metropolitan more
California: Coastal Slope Monitoring
The North County Transit District (NCTD) of San Diego County, California, determined that three more
Ohio: Monitoring Sinking Highway
When the Ohio Department of Transportation (Ohio DOT) was preparing to widen Interstate 77, more

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