eBay is a good source. The trick is finding one that's got a current calibration.
I've got a single 2" long 140 (or 160 Watt?) and I think it's pretty long, for the purpose.
0.1 deg C resolution might be fine for you. I'm still after 0.01, to calculate the power that the water block picks up. RTDs aren't really necessary, because I'll be running them in differential (i.e. I need delta T, not actual temp) but the heat die temp needs to be accurate.
There's a lot of factors that go into selecting a temp probe. Accuracy, repeatability, response time,... then there's the whole calibration thing. pHaestus is working with 0.1 deg resolution, and it's limiting him in measuring the power pickup of a water block, because the delta T at 2.0 gpm is getting pretty close to the 0.1 deg C resolution.
Not easy to do 0.01.
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