RTD off a few degrees, as good as i can expect?

I put together a simple RIMS temperature control panel with an Auber PID controller. Thanks to this forum it was actually one of the most successful DIY projects I have undertaken. The hardest part was painting the box......

Anyway, I tested the RTD this evening and I got:

Ice water = 33 F
Boiling water = 210 F

Based on the current barometric pressure at my altitude it should be 32/212

Is this as good as i should expect or should I try ordering a new probe?

I guess I could "calibrate" the probe but if I adjust it to 212 when boiling it would just shift it to 35 degrees at the low side right? Am I overthinking this? I do that sometimes...

Do you have a high quality digital probe thermometer? You could compare to that.

I always had a beast calibrating to ice water and boiling water. Like your results, it was always close, but never dead on.

Unfortunately I don't have a thermometer I trust to +/-1 degree...

All I have are the laws of physics and a lot of water.

Are you testing with distilled water? Also, getting to 32 flat is tough even with the best slush mix.

I agree that a legit thermometer such as a thermapen would be great to calibrate with, but in it's absence you are using a good method. You really only care about accuracy at mashing temps 145 - 158.

I am using RO water, not distilled although with a TDS of 7 it should be close. Like you said, I am really only worred about being accurate at mash temps. I might just adjust the boiling temp to 212 so it is closer at the high side and call it done.

It was my understanding they are only accurate when calibrated in a range. So if accurate at boiling, will be some off at freezing. I could be wrong.

milldoggy said:

It was my understanding they are only accurate when calibrated in a range. So if accurate at boiling, will be some off at freezing. I could be wrong.

Click to expand...

and will it matter once the adjustment is made to the offset for the hot range? Is the OP going to be measuring freezing temps with the homebrewing system? If not whats the concern here?

Just use an offset on the controller to compensate.

ChemEng said:

I put together a simple RIMS temperature control panel with an Auber PID controller. Thanks to this forum it was actually one of the most successful DIY projects I have undertaken. The hardest part was painting the box......

Anyway, I tested the RTD this evening and I got:

Ice water = 33 F
Boiling water = 210 F

Based on the current barometric pressure at my altitude it should be 32/212

Is this as good as i should expect or should I try ordering a new probe?

Click to expand...

Looks good for a low priced controller and looks within specs to me.
Check your vendors specs for your controller.

Finally got my RIMS tube and discovered that the "1/4" Threaded Connection" on the el'cheepo probe i bought was not really 1/4", not even close...

So i bought one from Auber like i should have in the beginning. They were great, seemed to know what they were talking about when i called them to ask questions over the phone.

Ordered on Friday afternoon, and it arrived a few hours ago (its Monday) you can't beat that. I also like the ability to disconnect the probe from the cord.

I will try the ice/boiling water test again tonight and see how the new probe does.

ClaudiusB said:

Looks good for a low priced controller and looks within specs to me.
Check your vendors specs for your controller.

Click to expand...

Good idea.

Spec says: ±0.2% or ±1 unit of full input range
Input range for PT100 = -320~1100ºF

So 0.2% of 1420 is +/- 2.84 degF so i guess my probe was technically in spec.

Is +/- 3 degrees really going to make a huge difference in the end? The different temperature ranges for different enzymes/phases are quite a bit larger than that, so I think you'll be good to go.

Simple test is get a high-tolerance 100 ohm resistor (0.1%) and connect directly the meter. Should read 32.0°F / 0°C. You probably don't want to spend the shipping on a single resistor from Digikey though.

The auber does have a temperature correction offset. Look at the manual and you'll see how to set it. Unfortunately, it's just an offset, so it won't fix your problem at both ends of the scale. Just figure out how much it's off at mash temps (i.e., 150°F) and then set the auber temperature offset accordingly.