Where is the best place to put the temperature sensor for a RIMS setup?

I can think of 4 places where it could be placed.
1) At the output of the RIMS tube
2) At the input to the RIMS tube
3) At the point where the wort goes back into the kettle
4) At the point where the wort comes out of the kettle.
1 and 2 have the advantage of having the control wire and power cord running more or less between the same places.
3 and 4 have the advantage of having the temperature sensor closer to the mash.
I’m leaning toward 2 right now because it has the advantages mentioned earlier plus it is not all that far removed from the mash itself. It is close to being the same as 4.
Does anyone have any opinions on this?

The temp probe will be controlling the RIMS element and thus the temperature of the fluid exiting the RIMS tube. I suggest that the best (and only in my humble opinion) place to monitor the temperature is in the immediate exit path of the RIMS. Placed anywhere else and there is a risk of over driving the element and thus overheating.

Also, if you experience temp losses due to wort tube length or placement, you can more easily evaluate the situation, understand it and compensate. Knowledge is power after all.

Just saying...

I agree - at the outlet of the RIMS tube. You may also want to put themometers mid way down your mash tun and at the bottom of your mash tun to see how effective you are.

You shoud see the temperature change from top down during a step mash & the speed of the change will tell you how fast your system's reaction time is.

At the outlet of the RIMS tube was my first thought. I reason to question that is that it will be hotter than the liquid in the pot. I hadn't thought about the pot getting hot from the top down.
Thanks for your opinions.

There is another reason to put the sensor at the outlet. If you put it anywhere else, like in the middle of the pot and the temperature drops, there is nothing preventing your RIMS from running over temp and denaturing your mash in an effort to bring the temperature up.

At least if you are regulating the output you won't go over temp. And if monitoring the RIMS outlet temp won't keep the temperature where it's supposed to be you have other problems.

For example, if you can see that your heater is cycling on & off but your mash is not being kept up to temp then you aren't flowing enough volume through your RIMS. And if your heat is on all the time & your mash is not being kept up to temp then your heater is too small.

Thanks,
I have moved the temperature probe to the output of the RIMS tube.
I'm doing BIAB with 120V and have to do the boil with propane so there is no insulation and thus a tremendous amount of heat loss during the mash. I thought about the potential of denaturing the mash at one point, but that dropped out of my consciousness during the build process.
I plan to bring the water up from room temp to strike temp with the RIMS tube and during that time I would like for the element to be at 100%, but I also want the PID to regulate once it gets there. That is what put the idea in my head of putting the probe at the input of the RIMS tube instead of the output. The idea was that I could set it up and leave it on its own and not have to watch and wait while it heats, but I guess if I’m not going to be there watching, then it doesn’t matter if it takes longer to get up to temp, does it?

Why don't you propane heat the strike water and then put a removable insulation sleeve on it during the mash?

PID works best where the control point is closely linked to the input point so that it gets very rapid feedback of the results of changing the input. Ie as it increases heating power it sees the increase in wort temperature.

The further away you put the probe from the heater, the greater the response lag and the worse the stability will be. If the controller increases power and doesn't see a temperature increase, it will keep increasing power until it does. Either it ramps the power to 100% and burns your wort, or it ramps very slowly and you get bad temperature control.

The problem with putting the measurement at the input is the temperature will over-run, particularly when bringing your mash up to temperature. And even after you are at temperature your mash temp will cycle because the warmer mash fills from top down.

Well, I tried it out this afternoon. I put the sensor at the output of the RIMS tube and let the pump run full bore. I heated 9 gal of water and had the SV at 160F. The water coming into the kettle (about 18" or less of hose after the RIMS tube) was barely warmer than what was in the kettle. This is a good thing because the PV on the 2352 was usually only about 2 degrees higher than the temperature showing on the Brewmomenter in the kettle. When it got to where the PID was controlling the PV and the Brewmomenter were right together.
The problem I have, and I've seen it mentioned in another thread, is that the PV settled in at 163 - 164 instead of the SV of 160.
Do any of you know what to do about that (other than setting the SV 3 degrees low)? Have you seen a thread mentioning this problem?
Thanks

naamanf said:

Why don't you propane heat the strike water and then put a removable insulation sleeve on it during the mash?

Click to expand...

I do plan on wrapping some insulation around the kettle and just tie it on so I can remove it for the boil.
I want to use the RIMS tube to get the water up to temp for a couple of reasons. The cost of propane, which won't be offset by only going partially electric, but more important to me is that I can set it up and forget about it for a couple of hours while it gets hot and if I forget about it for longer than that there is no harm. This afternoon with no insulation and ambient temperature at around 55 degrees it a little less than 2.5 hours to get 9 gal to 160 degrees. It should be better than that with insulation.

So for a set point of 160 the water was actually at 163? On the brewmometer as well as the PID controller? It sounds like you might need to let the system run in learning mode for a bit if its overshooting the set point.

It'll probably heat faster if you slow down the pump too

PeteNMA said:

So for a set point of 160 the water was actually at 163? On the brewmometer as well as the PID controller? It sounds like you might need to let the system run in learning mode for a bit if its overshooting the set point.

It'll probably heat faster if you slow down the pump too

Click to expand...

Sounds right. In terms of flow rate for the pump, I would think there would be a "sweet spot" where you have slowed it to have optimal contact time with the element. Too fast will not heat as quickly, too slow could scorch. At least that is the theory.

There can be several reasons for your PV to be set at 160F and over-running to 163F.

1. If the set display is at 160F and the actual display is at 163F then there is something wrong with the PV.

2. If the set display is at 160F and the temperature reaches 163F then starts dropping back down then you are monitoring the temperature at the wrong point, like at the RIMS inlet. Everyone forgets that when the RIMS heater turns on the temperature change is not instant, it takes time for the higher temperature to travel all the way through the mash tun. This is exact why you should monitor the temperature at the outlet of your RIMS tube. I have mine even closer - it's at the top of my RIMS tube.
http://www.instructables.com/id/Build-your-own-portable-Stainless-Steel-RIMS-tube-/

3. If your PV is set to 160F and the temperature measured by a independent thermometer is at a constant 163F then one or the other is out of calibration. K type thermocouples can be as much as 2F off which is why the temperature of anything being controlled by a thermocouple needs to be independently verified. But one good thing about a K type thermocouple is once you know the offset you can count on it. In other words, of yours is +1/2 degree off it will always be +1/2 degree off.

I found the thread where someone had a problem with overshooting and the solution was to auto tune. I did an auto tune and set the SV to 157 and the PV was dead nuts 157 as well as the Brewmometer at the bottom of the kettle. Life is good.
The sensor is in a T coming out of the top of the RIMS tube. I was going to put my senser in the RIMS tube like you did, but I got a 1.5" sensor instead of a 2.5" so it wouldn't have gotten all the way into the flow. The T screws into the place you have your sensor and my sensor is in the T so it is only about 2" farther downstream than your.
I'll post pictures if I ever bother to learn how.

PeteNMA said:

So for a set point of 160 the water was actually at 163? On the brewmometer as well as the PID controller? It sounds like you might need to let the system run in learning mode for a bit if its overshooting the set point.

It'll probably heat faster if you slow down the pump too

Click to expand...

I put the PID in auto tune and let it run and that fixed the overshoot problem. Thanks.
I can see that the water coming out of the RIMS tube would be hotter with a slower flow rate, but there would be less of it so the overall time should be the same. I will probably have to slow down the rate when I actually have grain in the kettle to keep from compacting it, or so I have read.

Glad that the learning mode sorted it out. PID can be a tricky thing to tune manually so when it works automatically it's always great.

The slower the flow rate the faster the water will heat up. The bigger the temperature change the faster it happens. You're probably also right that you won't be able to run at 9gpm whilst mashing.

I'd throttle the pump down and re-tune the PID setup, or at least check that it still works well at different flow rates, you probably won't want to be doing that when mashing.