Issue with temp probe reading stability

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atouk

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I have a electric setup I built that uses pt100 probes to take temp measurements for the PID controllers. The setup is still new and I am ironing bugs out, but this one has me stumped. The temp readings have started fluctuating wildly from the correct temp down to the lower limit and everywhere in between. I can effect this by moving the probe wire and can get the reading stable at the correct temp with a little wire wiggling, so I'm fairly confident the issue is not with the PID. What could be causing this? The wire is kept out of the way and is not being bumped or moved by accident. The probe itself passes through the side of the kettle and has a disconnect for the wire. The wire runs to a male xlr connector that plugs into my control panel. I soldered the xlr connector on, but the rest of the probe/wire assembly came built from the manufacturer.
 
I have a electric setup I built that uses pt100 probes to take temp measurements for the PID controllers. The setup is still new and I am ironing bugs out, but this one has me stumped. The temp readings have started fluctuating wildly from the correct temp down to the lower limit and everywhere in between. I can effect this by moving the probe wire and can get the reading stable at the correct temp with a little wire wiggling, so I'm fairly confident the issue is not with the PID. What could be causing this? The wire is kept out of the way and is not being bumped or moved by accident. The probe itself passes through the side of the kettle and has a disconnect for the wire. The wire runs to a male xlr connector that plugs into my control panel. I soldered the xlr connector on, but the rest of the probe/wire assembly came built from the manufacturer.

Sounds like a loose connection in the probe assembly. Probably need to get a replacement, unless you can figure out how to get inside the probe assembly to fix it.

Brew on :mug:
 
My pt100 has the same problem. I did nothing to it. I ended up tying the cable in a loop to the probe, it seems to be a bad connection somewhere inside the spring/relief on mine.
 
Not sure where you purchased from. I've found if you buy a 5 pack of cheap probes from ebay, one will likely have a connection problem like that. I had to throw away one that had intermittent issues after a couple months. The others have been good for over a year now.
 
Brewed over the weekend and I am going to have to try to take the connector apart and see what's going on in there. The temp was bouncing all over the place until I managed to work the wire into just the right angle to hold steady. It was like tweaking the ol' rabbit ears to get a clear picture! :D

Hopefully a bit of solder will fix things.
 
I have one PID that is a little flaky in its temperature control like what the OP sees in his equipment. I thought it was my PT100 probes, but I finally determined that they were fine when I swapped the probes between my PIDs and found that it was the PID and not the probes. I ended up putting the flaky PID on my HLT where exact temperatures are less of a concern.
 
Try plugging and unplugging (I think you have XLR connectors?) a half dozen times. This wipes oxidation or whatever may be on there off on both the male and female sides. This is not to say you don't have a cold solder joint in there too or rather than dirty contacts so do check that too but I could amuse you all afternoon with stories about my supposed electronic wizardry which was really simply cleaning connector contacts (while everyone else was out of the room).
 
Try plugging and unplugging (I think you have XLR connectors?) a half dozen times. This wipes oxidation or whatever may be on there off on both the male and female sides. This is not to say you don't have a cold solder joint in there too or rather than dirty contacts so do check that too but I could amuse you all afternoon with stories about my supposed electronic wizardry which was really simply cleaning connector contacts (while everyone else was out of the room).

You could also probably wipe them down with a Qtip or something smaller with a bit of isopropyl alcohol and let it dry off?
 
At my last rented apartment I found that my RIMS controller with a MyPin TD4 (I think) and PT100 read low by 10-20 F intermittently (but often, maybe more than 50% of the time) when I used one circuit in the kitchen, but behaved perfectly when plugged into the other circuit. This was repeatable over several brewing/cheesemaking sessions (I use the same controller for a sous-vide style water bath, but with a different PT100 sensor) with the same sockets having the same effects, so I'm guessing that this might have been an issue with noise on the power line for one phase only or something behaving oddly with the GFCI sockets. Maybe there could be a small intermittent DC offset on the power line that would affect the sensor reading? Maybe something from another appliance on the same circuit? Some kind of grounding/ground loop issue? Whatever it was, I guess it's probably a flaky PID unit that was highlighting the problem.

I'm speculating wildly here as I never worked out what it was since using the other circuit solved the problem. At work in the lab we bias superconducting devices and much more precise temperature sensors with sub-microvolt precision and noise and have to watch and mitigate many of these issues, but I've not seen anything quite like that (using much more expensive electronics) where the choice of power circuit affected things. I haven't tried the controller at my new house yet.

I'm pretty damn sure that this is unrelated (jiggling the sensor wire didn't help at all for me, but touching the cable could potentially affect ground loop or noise issues), but I thought I'd put this report of temperature sensor/PID weirdness out there in the hope that someone knows what's going on and can give others a potential* bug to check out before they buy new sensors.


* no pun in 10 did. ;)
 

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