Home Forum Software What is "WDT"? And other values

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    The uRADMonitor has a bunch of values in its output with labels that I don’t understand. Can anyone shed some light on what the values are and what the units are? Specifically the following fields either have values I can’t understand or can’t figure out the units for, or have labels that I can’t identify: type hw sw VOL VOC WDT INT http

    If there’s any documentation that lists everything and defines it all, that’d be great.


    Type is the device class as defined in specs v1. Originally the model A was 1, the A2 was 4, the KIT1 was 5 , the D was 6 , the A3 was 8.
    It was the first digit of the Device ID. You’re using an A3 so it starts with 8.

    The second digit was a code for the Geiger tube used. 1 was SBM20 while the 2 was SI29BG. 4 was LND712. So your device ID starts with 82.

    Having the Geiger tube encoded in the device ID started to loose meaning with the recent units that only do Air Quality monitoring and have no radiation sensors. So the device class defined in specs v2 became two digits big. As an example, the device class for an INDUSTRIAL is 14.

    HW is the hardware version. Each model was multiple iterations. With the A3, HW103 and HW105 were the most common. You can still see a first HW100 (first iteration) here: https://www.uradmonitor.com/?open=82000001 . This particular unit is not only part of the first production batch, but it is also the very first uRADMonitor A3 unit produced. It is installed on a bus in the city of Cluj Napoca. Its data is linked to an external GPS module so we have the Air Quality measurements mapped to location. Here’s how that looks: http://www.uradmonitor.com/cluj

    SW is the firmware version, the actual software running on the devices themselves. This can be updated from time to time, as I push out newer software versions to fix bugs or add new features: https://www.uradmonitor.com/firmware-upgrade-a3-wifi/

    VOL is the voltage on the Geiger tube. It is configured to 380V in software, as the Geiger tube needs this High Voltage to run. It is low current, so you cannot electrocute yourself, however touching the internals while the device is running can give you a little shock. So don’t do it.

    VOC is the Volatile Organic Compounds sensor. You can read about those here: https://www.uradmonitor.com/products/?sel=4 under the “IMPACT” tab or in the datasheet here: https://www.uradmonitor.com/wordpress/wp-content/uploads/2017/02/datasheet_a3.pdf

    WDT is the watchdog, a timer that will reboot the device when it reaches a certain value. Normally this doesn’t happen, as periodically the Watchdog is reset to 0 if all critical operations are successful (mainly reading the sensors and communicating the data to the server). Resetting the watchdog is called “patting the dog”.

    INT is the time interval for sending data. It is set to 60seconds on the A3. This means that every minute your A3 will send data. This can be customised.

    HTTP is the server’s return code when the A3 send some data. 200 means OK. Anything else means error. There can be various errors codes. These are the standard HTTP Error codes, you can find documentation about them online if interested.

    Let me know if you have any additional questions here, and thanks for your interest. This is much appreciated.



    Finally got around to writing the software that reads this data. Thanks for your reply. 🙂

    I continue to be very happy with the A3. I recently especially appreciated the wide range of allowed input power; I was able to change from using the transformer to using a 24V Passive PoE switch to power the unit remotely, which was very convenient.

    I have a follow-up question:

    How do I convert the resistance number from the VOC sensor to mg/m³? I tried looking up the sensor datasheets but couldn’t find the answer. The datasheets suggest that clever algorithms based on the relative humidity and other unstated factors can be used to determine an AQI-like abstract value of “cleanliness” for the air, but I would prefer a more concrete unit, even if such an algorithm was well-defined.


    Well there is a curve that shows resistance to alcohol ppm equivalence here: https://www.uradmonitor.com/metal-oxide-voc-sensors/

    But please understand that VOC means a mixture of substances and you cannot compute a generic VOC ppm due to the unknown nature of this mixture. Best you can do is to estimate carbon concentration or do equivalence to various substances such as alcohol. In my opinion it is not worth it as it doesn’t bring any new information, you’ll see the same graph shape, only the figures will be different as your approximation function will be linear. You already have the “VOC-AQI” for that.

    Alex Khassapov

    Hi Radu, I also had to spend time to find some definitions, i.e. what’s CPM?
    Do you have the description for all possible readings? If not, can you please write it down somewhere in API documentation.


    Hi Alex,

    CPM means “counts per minute” and corresponds to geiger tube discharges per minute.
    The units are pretty self-explanatory…if you still have questions, feel free to ask them here.


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