Anyone know about thermocouples?

[hoppyscotty]

I have a long thermocouple for my RIMS system, think its about 50 or 60 cm long. I'm thinking about reconfiguring it as I think the tip is a bit too close to the element and might be picking up some heat from the element rather than measuring the wort value which can throw the control into a bit off and it starts overshooting. In the new configuration I'm thinking of I'll be using a much shorter thermowell so probably only 10 to 20cm of the tip of the thermocouple will be in the well.

Do these things measure the temp at the tip only or along the entire length of the probe? I thought it was the former but just checking. I don't fancy pulling apart my control panel to swap out the probe. Also I use the same thermocouple on my HLT when not mashing.

Thanks.

 

[LeeH]

The element is on in tip, normally the first 5mm with a little heat sink compound. You want it close (ish) to the element to prevent you scorching the wort. You PID controller needs to be auto tuned.

You’d be better off using a RTD (PT100) for this application.

HTH.

 

[JockyBrewer]

You only need the last 1cm or so in the wort.

Do you also measure the temperature in the mash itself?

 

[hoppyscotty]

I keep an eye on the mash temp too. There is pretty close correlation but the PID measured temp will occasionally go silly and run away, but of course the mash temp remains pretty steady so I think my thermocouple tip is too close to the element and picking up the heat of the element which will be much higher than wort temp as the wort is being continually pumped over the element so you get minimal heat pick up from element to wort. So thinking about installing a T piece at the top of the rims tube so the thermocouple measures the wort temp on exit of the rims tube instead of protruding down into it and sitting right on top of the element. Any temp rises in the wort will be picked up immediately as it’s only moving a few inches, but probe tip will be well away from the element. I don’t see any signs of wort scorching on the element after mashing so satisfied the flow rate of wort over the element is preventing scortching.

 

[JockyBrewer]

Well you have more experience than I do in RIMS, but that sounds reasonable to me.

With regards to the Thermocouple vs RTD sensors, I don't think for home brewing purposes it matters. A good quality thermocouple is better than a bad RTD.