Freezer Defrosters and Monnit Sensors

If a Monnit sensor probe or the sensor body operates near a freezer or cooler defrosting unit, an unintended influence can affect sensor operation.

Since defrosting units often consist of electrical coils, the defrosting unit can affect the sensor radio communication through EMI interference. The defrosting unit can also cause unexpected peaks and valleys in your sensor’s reading history.

If you have Rules set to trigger due to temperature excursions but do not account for the temperature fluctuations caused by the defrosting unit, you may receive unexpected alerts.

This article will provide details on such an issue.

Patterns

Freezers often have defrost cycles every 3, 6, 12, or 24 hours (though this can vary extensively). If your sensor consistently loses connections, look for patterns in the signal history and temperature oscillations. You will generally see a significant signal loss and then a signal recovery after the defrost cycle has been completed.

You may also see temperature oscillation when the defrosting unit is running. If you are able to review the defrost cycle schedule or check with your freezer manufacturer, it is worth comparing the defrost cycle schedule with your sensor’s signal history.

Missed Communications

When a sensor is installed and operating near a defrosting unit, the EMI interference will cause the sensor to miss communications with the gateway. This may also cause the sensor not be able to reconnect to the gateway. In the below example, a customer’s freezer would enter a defrost cycle every 3 hours.

As a result, the sensor would often have signal degradation during these times. Reviewing the signal history and considering patterns can help determine this.

Temperature Spikes

In addition to the signal fluctuations, you may also see temperature fluctuations occur if your sensor’s temperature probe is within the range of the defrosting unit.

This temperature fluctuation can often cause a temperature variance of tens of degrees. If you see unexpected temperature oscillation, this is usually the cause. Moving the sensor probe away from the defrosting unit might be necessary to avoid sensing the defrosting cycles.

Unintended notifications

You may find notifications triggered as a result of Inactivity or Temperature notifications being triggered from the defrost cycle. You may consider configuring Delayed Actions or using the Notify After Aware Period notifications to address this.

If you need additional guidance, please contact support@monnit.com.