If the CS215-L is displaying a -100 (actually a -99.999) for temperature and RH, what is wrong?

If the -100 is actually -99.999 for both temperature and RH, this is an indication of what should be a rare condition. This indicates that the microprocessor in the body of the probe cannot communicate with the sensor element correctly. To be more specific, the communication between the microprocessor and the sensor element includes a CRC check. The microprocessor tries up to three times to get data with a good CRC. If it does not succeed, its sets both values to -99.999.

The following are some reasons why this might happen, as well as some suggested solutions:

  • There is a source of very strong RF interference near the tip of the probe. Check that the probe is not mounted close to a cellular telephone or radios.
  • The sensor element does not have a good connection with its socket, or the socket is corroded. Remove the cap of the sensor, and inspect or reseat the sensor element.
  • The sensor element is faulty. A replacement element can be ordered from the Sensirion website.
  • There is an internal connection issue or dry solder joint inside the sensor body. In 2011, some sealing glue ran down inside the probe’s body into a connector, which caused a poor, intermittent connection. Measures were taken to prevent this from happening in CS215-L sensors produced later.

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