FAQs Frequently Asked Questions about Our Products and Solutions

Using a CS650 or a CS655, why would the volumetric water content value be NAN or 9999999?

The CS650-series sensors have several logical tests built into their firmware to ensure that the sensors do not report a number that is known to be erroneous. Erroneous readings are either outside the sensor’s operational limits or outside of published accuracy specifications.

A reported value of NAN or 9999999 does not necessarily mean that there is a problem with the sensor hardware. The conditions outlined below can lead to a value of NAN or 9999999 for volumetric water content.

SDI-12 communications issue

If all of the following are true, there is likely an issue with the SDI-12 communications between the sensor and the datalogger: the sensor is being polled with an M! or M3! SDI-12 command, the volumetric water content value reported is NAN, and subsequent values are all zeroes or never change. Possible causes include the following:

• The sensor is not powered. Check to make sure that the red wire is well connected to a 12 Vdc source and that the black wire is connected to datalogger ground.
• The sensor signal wire is not connected properly. Ensure that the green wire is well connected to the universal terminal or control port specified in the datalogger program.
• The sensor has an SDI-12 address that does not match the datalogger program.
• The sensor has cable or lightning damage.

Permittivity is greater than 42

The CS650 and the CS655 calculate real apparent bulk permittivity of soil and then use the Topp et al. (1980) equation to convert permittivity to volumetric water content. A permittivity value of 42 is the upper limit for making that conversion. This is equivalent to a volumetric water content of 0.52.

If the M3! command is being used and the permittivity reading is being saved as part of the data set, volumetric water content  numbers higher than 0.52 may be calculated by applying the Topp et al. (1980) equation or another equation to the permittivity reading. This may be done in the datalogger program or in post-processing software, such as a spreadsheet. 

Permittivity value is NAN or 9999999

Because volumetric water content is calculated from the permittivity reading, conditions that cause the sensor to report NAN or 9999999 for permittivity will give the same value for volumetric water content. 

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