Sensor open with Honeywell 5821 and T280R for freezer monitoring

Support
, ,
1

I set up a Honeywell 5821 and T280R for freezer temp monitoring per this thread:

ADC shows “Below temp threshold”, and the GC2 panel reports “freezer temperature (open)” as a triggered zone. So I don’t get a “ready”. It’s set as 24-hr aux. My thermometer shows -3.6ºF. I did get an alarm after setting up the sensor. That was intentional to ensure that it’s working.

DIP switches are 1: off, 2: on. It’s on loop 2. I get about 600kΩ across the terminals with the probe connected to the 5821. (Incidentally, having trouble finding the resistance specs for the T280R.)

Anything else to check or change? Thanks

2
I get about 600kΩ across the terminals with the probe connected to the 5821. (Incidentally, having trouble finding the resistance specs for the T280R.)

How long since you tripped the alarm and how did youtest? Did you warm the probe well past the requirement? Be sure to check the operational expectations for that sensor. To restore, the temp will need to drop below 7 degrees for more than 4 minutes.

600kohms would indicate a temp reading slightly above what is required to reset still. This link has the T280R resistance chart.

3

Thanks for that info, and especially the spec sheet. It looks like my sensor is slightly out of spec, but is working (for now) if I move it to the bottom of the freezer.

Incidentally, the 5821 appears to go an alarm state almost immediately if the sensor wires are disconnected. That’s reassuring.

Looks like the T280R is a 100k NTC thermistor with a beta value of about 3800K, so substitutions shouldn’t be too hard.