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why does the digi humidity sensor have a negative humidity ?

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I have 3 digi L/T/H deployed. After a couple of weeks one of the sensors starting sending a negative humidity value (using digi formulas for calculation). A week later another sensor did the same. Does anyone know why are these sensors sending negative values?

Thank you
asked Feb 21, 2017 in RF Solutions and XBee by albe New to the Community (4 points)

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1 Answer

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What is your voltage source? Could the batteries be running low?
answered Feb 21, 2017 by mvut Veteran of the Digi Community (13,036 points)
Thank you. Batteries are new. The humidity errors began when the humidity lowered from value when installed. I notice the two sensors that are reporting incorrectly  send two samples one after the other - first sample is correct - second negative or really low. 1 sensor reports one sample correctly - 2 reports 2 samples and the last is incorrect. All 3 sensors were configured the same. The L/T/H devices seem to be unstable and prone to error.
How are you determining that you are getting two values? What are you using to collect the data from or issue the commands from?  Are you sending the IS command or are the module sending samples after x number of samples are taken?
Thanks for your response. The L/T/H sensors are deployed in our automation platform where we use xBees. Our software picks up radio messages from all sensors and relays. Here are the messages for the 3 digi L/T/H sensors.
.../40AEC262/ad1 2017-02-21 14:40:18|Cockpit|LightLevel|1201.17
.../40AEC262/ad2 2017-02-21 14:40:18|Cockpit|Temp F|89°f
.../40AEC262/ad3 2017-02-21 14:40:18|Cockpit|Humidity|33%
.../40D58F83/ad2 2017-02-21 14:41:07|Galley|Temp F|63°f
.../40D58F83/ad1 2017-02-21 14:41:07|Galley|LightLevel|76.25
.../40D58F83/ad3 2017-02-21 14:41:07|Galley|Humidity|56%
.../40D58F83/ad1 2017-02-21 14:42:10|Galley|LightLevel|87.98
.../40D58F83/ad2 2017-02-21 14:42:10|Galley|Temp F|72°f
.../40D58F83/ad3 2017-02-21 14:42:10|Galley|Humidity|-14%
.../40AEC249/ad2 2017-02-21 14:42:14|AftCabin|Temp F|66°f
.../40AEC249/ad1 2017-02-21 14:42:14|AftCabin|LightLevel|91.5
.../40AEC249/ad3 2017-02-21 14:42:14|AftCabin|Humidity|64%
.../40AEC249/ad1 2017-02-21 14:43:17|AftCabin|LightLevel|110.26
.../40AEC249/ad3 2017-02-21 14:43:17|AftCabin|Humidity|-7%
.../40AEC249/ad2 2017-02-21 14:43:17|AftCabin|Temp F|73°f

All 3 are configured the same. We are testing these to see if we can use them in deployments.
This is going to be something in your code that is causing this and not int XBee or the LTH sensor.  I would suggest that you add some break commands or print functions to help determine where the issue is.
Thank you.. Our code has been thoroughly tested and has been running for over a year in different deployements. It the same code that processes all sensor data. If our code was at fault we would see the errors on all 3 sensors and other sensors deployed through the xBee network over deployments. Errors are consistent from 2 of the digi l/t/h sensors. I am sure based on our experience there is something wrong with the 2 digi sensors. Maybe a setting that does not show in xtcu. The digi l/t/h/sensors are difficult to configure.
Other than enabling the specific ADC lines, sleep mode, and how often to sample the data, there is nothing else to enable or configure on an LTH sensor. That is all there is to that product.

What I would suggest then is to move the two devices in question to your office and see if they do the same thing with XCTU and a module connected to a PC.
Thank you.. We tested these with XCTU when they were deployed. The 2 sensors sent 2 samples as they currently do, however the values were the same until humidity dropped then the 2 samples from the 2 sensors began sending different values. We plan to pull the sensors out of the deployment due to errors. Again thanks for your responses.