help with temp probe and PID on recirc system

[Adr_0]

The mash is the important temperature, but you should make sure your wort flowing over the element doesn't get too hot. It will need to be hotter than the mash to raise the temperature of the mash though.

The outlet should be a good place for it as it's safest for wort enzymes and scorching prevention. As described above you should be able to set it to your mash temp with a decent recirculating flow, then watch the output on the PID display go down to 0-10% output. Measure the mash with your calibrated thermometer and hopefully it's close and then stop the flow.

The downside is that ramp control is counter-productive when you measure directly on the element so you shouldn't use it. You can impact your ramp time based on changing the recirculation rate: high flow = fast ramp if your element can keep up. You also can't directly see the mash temp as your probe is elsewhere.

I would probably start with a gain of 3-4 and an integral time of maybe 10s and see how you go. Auto tune if you wish.

 

[ben frazer]

Thanks, it is starting to become clearer to me now. I will try with only returning to the top of the urn, and with the probe at the outlet of the urn, prior to the pump. When you talk gain, which parameter is that on the PID (ie, is it the P, the d or something else? I assume the integral time is the I? As I said, I am struggling to get my head around PID's.

I know every system is different, but I would be really interested to know the PID parameters of someone who is running a recirc on a standard 40litre urn with a 2kw element. Just to give me a starting point.

 

[Adr_0]

P is gain = multiplier. The temp probe type/range must be set correctly on the Rex.
I is integral time = seconds where it measures the accumulated error
D is derivative = set to zero for now.....

 

[Adr_0]

How big is your RIMS tube in litres?

 

[Adr_0]

Ah. Just read your original post.

In that case, you probably want gain of 10-15 and start the integral at 60s and work back to maybe 20s if it falls short of your set point.

 

[geneabovill]

Is there a chance that the PID probe is calibrated to read correctly at, say, 20°c but when approaching mash temps it's well out of whack? I didn't read in the OP whether or not you calibrated at mash temps or not..

 

[ben frazer]

Thanks Adr_. I will give that a go as a starting point.

Ruckus, the offset against the calibrated thermometer is constant through all temps up to boiling. I haven't however tried running without the element on so will run this check tonight. That is to fill the urn with water and check inline probe reading versus calibrated probe reading without the element causing any potential hotter draw into the recirc line. Maybe, as suggested, as the water is being drawn in through from the bottom of the urn, nearish to the element, it is drawing hotter liquid than the average temperature of the liquid in the urn. Turning off the element and letting it recirc for a while to stabilise should prove whether this is the issue or not I guess.