Temp probe location

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rehabs_for_quitters

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In the middle of getting everything together for a 3V build, now I am going to use a hems coil in a separate vessel for the hex and am going to put a temp probe in the mash tun and also on the hex, where would be the best place to put the probes and to take the mash temp reading from, I am thinking outlet of mash tun and outlet of hex but having never built one before not 100% sure where I would get the most accurate readings
 
I am adding an extra couple of PID's and 40amp SSR's power outlets plus temp probes as I scored a massive stainless box that's got loads of room and then I can add an extra kettle or two for long sour mashes, so thought why not stick and extra temp probe into a vessel in the mean time hence why I thought mash tun, but the hex outlet it shall be, cheers
 
TL;DR. I installed an MT probe under half way up the mash volume to compare with my HEX out temp to have confidence heat was being transferred to the grain and the mash temp was uniform throughout.


This is an interesting question. There are different approaches.

Some people install the probe so that it reaches into the 'centre' of the grain mass. I think this is reasonable because it helps assume a reasonably accurate 'homogenous' temperature for the mash. But there will be a gradient top to bottom depending on vessel insulation levels. Arguably, if you have perfect insulation in your vessel and you've stirred your water and grist so its temp is homogenous then your probe could be installed anywhere - in an ideal scenario that is.....but not real world. You'll recirc with HERMS, so volumetric flow rate matters then for HEX outlet only scenarios. If the flow is minimal because your grain bed is a little tight then it may no longer be a reliable indicator.

Also, temperature losses between HEX out and MT in need to be known. On the flow rate issue, your MT geometry may come into play. If it is uninsulated and tall, then without enough flow rate evenly distributed over the mash you could loose more joules of heat off the vessel skin than you would want, possibly meaning your mash temp is within your target for only the top part of the grain.

I installed a MT probe under half way up my average mash volume (the water/grist volume - not vessel) so I know what the delta is between my HEX outlet and how that impacts on the mash. Good for diagnosing any channeling you may have. Calibrate both sensors in that scenario. without the MT probe I'd be watching the HERMS element to see that it wasn't busting a gut trying to heat cold wort from the bottom of your MT.

A problem I've encountered with MT probe is that the thermowell gets in the way of my falst bottom removal. a slight hassel so keep that in mind for whatever cleaning plan you may have.
 
I will be recirculating back to the side of the mash tun but could just as easily return to a stainless plate sort of thing to the centre top of the grain bed, I'm presently using gas recirc biab but striving for a bit better temp control of the mash to get everything as consistent as possible, I will have four PID's and temp probes so can chuck one down the grain be also
 
I'm 1 year in with my 117L 4V system and I'm still getting to know how she behaves. When I have any doubt about what's going on I think it's safer to measure the process variable directly.

I also have a 500mm narrow thermowell is use for temp regulation on my primary fermenter. When it isn't being used to measure the ferment core, I chuck it in the grain with the PID's PT100 in it. It's great, I can move it anywhere within the mash. I've picked up 3-4deg differences between my fixed probe and the 500mm. So that tells me to stir, or that my recirc is not flowing evenly through the mash.....and why would it. Path of least resistance right?

For me, set and forget hasn't been working out. And if you have four of those sensors, then I'd get them all reading something. I reckon once you know how your system operates you could do away with one of then and maybe just one for the HEX outlet.

"If you don't know, you don't know....you know?"

In any case, the amylase window is fairly wide so I hope I'm not sounding like I want it within +- 0.5deg. :)
enzyme_activity_one_hour_mash.jpg
 
You want your temperature measurement for the PID control to be as close as possible to the heat source. In your case, at the heat exchanger outlet. However, do put a regular thermometer at the outlet from your mash tun so that you can see when the entire mash is up to temperature. Be sure to calibrate all your thermometers and probes!
 
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