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BACnet high limit false alarms or incorrect display


  • I have a BACNET datapoint that is configured as "Analog input," with the point properties set to convert W to kW, and record "When point value changes" with a tolerance of 0.1.

    This point has a "High limit" set to 18.5 for 60 seconds.

    The pop-up graph on the graphical view page (ma-core 2.8.8) shows the data varying between 0 and 15, and a red dashed line at 18. The vertical axis is labelled "kW."

    According to the logs, the point value has not exceeded 11kW, but the "High Limit" has triggered an "Urgent" alarm event multiple times, typically when the load being measured is turned on. Since the data has not exceeded the event detector threshold, the event should not have occurred.

    I suspect that internally Mango is not accounting for the data conversion from W to kW when setting the alarm threshold. Do the following point properties use "unit" or "displayed unit?"

    • Tolerance
    • Point value logged
    • High limit
    • Low limit
    • etc

    Each numerical field should be labelled to make it clear whether the attribute is using the instrument units or the displayed units. The current data_sources page is ambiguous in that regard.

    It seems that Mango is displaying the 18.5 dashed line as kW, but is using 18.5W for the High limit detector threshold. The fix could be to change the event detector value to 18500, but then the vertical scale of the graph would be squished and display the historical data as a flat line along the bottom of the graph. What is the recommended fix?

    Thanks.


  • Hi Pedro,

    The "Convert unit for display" is only for display purposes. So, the limit does not use the converted value. Therefore, all four of the things you specifically asked about do not use the post-converted value.

    The issue with the limit lines not being converted is here: https://github.com/infiniteautomation/ma-core-public/issues/684 as I suspect you know. I did just recently fix that but it isn't released yet. I'll email you an override.