Craftbeerpi PT100 temp reading

[frontiercdk]

Hey guys,

I just hooked up two pt100 rtd's through adafruit max 31685. I want to use craftbeerpi3 to control three fermenters . I have three adafruit 31685's hooked to the raspberry pi and pt100 rtd's attached to them. I only have probes on two of them currently (forgot to order the third one).

When I first hooked them up, they both read fine for a while (30-45 min). Then I got occasional high spike (like 350F). The spike was just a blip lasting only a second or two, then it returned to reading the correct value. After a while the blip became higher (1,811.83F). The duration got longer as well. I left it running last night and checked the log. It spiked and read correctly in long intervals (like 30min correct,45 min incorrect).

The 1,811.83F reading is the default reading when there is no probe hooked up.

I checked connections and "wiggled" wires for hours.

Does anyone have any ideas for me,,,, I am kinda at a loss

 

[jangevaa]

Possible EMI issue from a nearby compressor starting up/running?

 

[frontiercdk]

Good, idea jang, but there is nothing close or big near by.

I checked my soldering and wires again... and again... and again...could not make the fault occur through physical movement.

I open / close programs and you tube videos to tax the raspberry... couldn't get it to fault that way.

I just left it alone running. Checked the sensor logs every once in a while. It clunked along, randomly falling into misreading. I left it over night and checked the log the next morning. It ran all night properly. Cleared the log and let it be. Ever once in a while I wiggle wires beat it around a bit. It has now ran for over 26 hours with zero faults. The temp is freakishly accurate.

Is it possible the rtd has to "break in"?

Anyway, thanks jang for the idea

 

[frontiercdk]

Update.. first two probes still working perfect. I added another pt100 sensor and the same thing happened to it. Went crazy and then smoothed out and is working fine...

 

[frontiercdk]

Update... still working flawlessly