When I did a sous vide steak for the first time I set my pid to 130 and let it do its thing in my hlt till it got to temp according to my pid. I was curious so I just happened to check with my thermoworks rt301wa. It was 10 degrees low. so I adjusted the temp differential and everything went on fine. Next time I went to brew I checked the temp with my pocket therm and it was 10 deg high with pid set to 160 so I adjust temp differential and all is good. I was just wondering if other people's temp probes are only accurate in a narrow range. These are the temp probes I'm using http://www.ebay.com/itm/RTD-PT100-T...446044?hash=item58f3cd641c:g:NMAAAOSw-KFXe9Ju with and 14 gauge extension cord going to a xlr connectors then stranded 12gauge wire to pid.
Temperature probe accuracy
- Thread starter Toejam792
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How close was the ST301WA probe to the PID's temp probe when you did both of the checks. A Pt RTD shouldn't deviate much from the ideal temp vs. resistance curve for Pt. The magnitude of the deviations you observed are unexpected.
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Dfitz
Well-Known Member
An accurate calibration will usually require two temp readings. One at 32F and another at 212F. This is according to NIST.
Toejam792
Well-Known Member
How close was the ST301WA probe to the PID's temp probe when you did both of the checks. A Pt RTD shouldn't deviate much from the ideal temp vs. resistance curve for Pt. The magnitude of the deviations you observed are unexpected.
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My probe is in a tee at the bottom of my hlt, I stuck my thermoter in as far in as i could about 5-6". I run a tan ebay pump and recirculate with whirlpool when I heat the water so there shouldn't be much temperature stratification, maybe 1-2 deg but 10 is a lot. I was just wondering if the wiring makes a difference. My cord is about 10' long would the line length cause resistance issues?
I get that, but say I calibrate it at 32 deg and its off say 10 deg at 212, so i re calibrate for 212 now its off 10 deg at 32 is there a way to change the resistance curve on a TA4-SNR?
augiedoggy
Well-Known Member
I had no problems with the ta7 or any of my td4s and temp probes in my old setup..(This doesnt mean you dont have a defective probe or pid) I will say that unless your actually recirculating the wort through that tee while measuring the temp will be off. You probably already know this though and are recirculating through it when measuring. the best way to compare it to remove the probe temporarily and test with a secondary thermometer in the same area at the same time.
I have my probes mounted right in the kettle at level with the heating elements and find that even there the temps fluctuate when I give my kettle a stir so the temps arent really even throughout the whole kettle. when Im boiling around 210 degrees and things get rolling I find the temps are actually the most even.
Pt100 probes should be accurate and repeatable. The probes leverage the physical properties of Platinum, so my guess is something is up with your wiring or the PID itself.
When checking one probe/thermometer against another, you really want the active portions of them to be within about 1/4" of each other.
The extension wire shouldn't make a big difference for PT100 RTD's, as long as all three wires are the same, connected the same way, and the connections are secure. Loose connections could cause temp reading errors.
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I don't use PT100 probes any longer, but when I did, I had a problem with one of the connectors (little xlr type thing Auber sells) getting corroded. I would get 10-20 deg jumps when I bumped the connector. I had to get a Qtip and denatured alcohol out a few times mid-brew to fix it.
Ideally, there are NO connectors in between RTD sensors and their termination points. RTDs are relatively low impedance (Pt100 = 100 ohms nominal), so any minor differences in the resistances as a result of interim connectors will affect readings & accuracy.
I say ideally, because hard wiring without disconnects is usually not ideal!
I say ideally, because hard wiring without disconnects is usually not ideal!
DVilleBrewing
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Do not know if it makes a difference, but Rtd cable typically uses 22 to 24 gauge wire. Maybe the 12 to 14 gauge you are using could cause problems?
Larger wire is actually better for RTD extension cables, as it has less resistance per foot. Contact resistance at connections/connectors are likely to be more of a problem.
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Toejam792
Well-Known Member
Thanks for all the replies guys. I figured thicker wire would be better. My connections are soldered at the quick disconnects so they should be good I haven't tried to wiggle them to see if it's some loose sexing, I'll try next brew day. I'll also put my pocket probe closer to the pt1000 but like I said I was recirculating the whole time my heater was on so I doubt it was 10 deg difference, maybe 1-5 deg. but 10 seams excessive.
When I first wired my fermentation fridge up, my inkbird was froze reading the same temperature for like an hour...I finally heated up some water and tested it with a digital probe and it was accurate...put it back in my fridge and it started working fine. You aren't the only person who has had strange things happen with sensors...probably aliens I'm sure.
Loose sexing is usually a good thing.
augiedoggy
Well-Known Member
lol
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