Placement of temp sensors on mash tun/ HERMs

[brewbear]

Where do people recommend placing temp sensors on a mashtun and HERMS set up?

One sensor or two?

I got my hands on an insulated 20L vessel (unheated tea urn) and have knocked up a tesco kettle herms. I'll be putting one sensor on the entry to the mashtun (so wort will go HERMS > tubing > mashtun entry tap > tee piece with inserted PT100.

This will measure post-HERMs temps, but not the mash temp. Do I need/ would I benefit from a sensor in the middle of the mashtun or on the mashtun exit? [or maybe I could once check the difference between mashtun centre temp and post-HERMs temp and use this differential to adjust future HERMs temp settings?

I'm reluctant to drill the walls of the insulated mashtun unless absolutely necessary. Would a sensor on mashtun exit do the job? (mashtun> tap> teepiece with temp sensor> tubing> pump> tubing> HERMS)

The PT100s will be connected to PIDs.

Any advice gratefully received.

 

[sponge_]

Temp probes should really be placed after the heat source (outlet of HERMS), as it will be the highest temperature in the system. The mash will lag behind a bit but you'd rather bring the mash up to temperature that way than having the HERMS heat the wort to >80'C to try and control the mash temp that way.

When I was running my HERMS system, I had a tee-piece on the outlet of the HERMS for the probe which was used with my PID controller, and manually tested the temperature of the mash with a handheld thermometer. It normally lagged a couple of minutes from the HERMS temp.

 

[brewbear]

Thanks, Sponge. I'll certainly have a PT100 between HERMs output and mashtun input. My main question is whether to add a second sensor on mashtun output (or whether to just manually check the differential between mashtun internal and HERMs output once and use that to adjust calculations).

Perhaps (for cost reasons) I'll stick with just the HERMs output sensor.

 

[sponge_]

You can always get a dial thermometer (or PT100 with thermowell) installed on the mash tun to measure the temperature of the mash. That way you always have an easy way to see what's happening in the mash. You're not going to be controlling the PID using that so anything that will give you an accurate reading will do.

I used to have one (dial thermometer) on my mash tun but didn't install another when I upgraded my system. No reason besides knowing rough lag times and measuring with a portable thermometer.

 

[brewbear]

Thanks, Sponge: appreciate the notes on this. I think I'll go without drilling the walls and just calculate rough lag times.

 

[peebee]

You can always get a dial thermometer (or PT100 with thermowell) installed on the mash tun to measure the temperature of the mash...

Like everyone says above, the sensor wants to be on the HERMS outlet (mashtun inlet) from a "control" point of view. But as "sponge" says, a dial thermometer on the mashtun is a comfort to have (in addition to the one on the HERMS outlet - that's the one you can "control"; the mashtun will lag behind the HERMS outlet during changes to temperature).

What I'm currently doing is attaching cheap temperature sensors (�£1.50 a pop from China) on the HERMS inlet, HERMS outlet and HERMS jacket inlet (my HERMS coil isn't in the HLT like usual, its an external counterflow heat exchanger which doubles as the cooler too) but again this is for the comfort of seeing everything working right. The important one is that one on the HERMS outlet because that's the one you have some control over.