PID R.I.M.S. Temperature NOT matching actual temp in mash tun

[IndyBlueprints]

I have a new rims system. I am using an Auberins SL-2352 PID. I did an auto tune using just water, with 155F as my target temp. Once I did, according to the PID, it is maintaining 155F. However, the Blichmann Brewmometer in the mash tun reads a consistent 148F. Even over time, it stays right there. To maintain 155F in my mash tun, I had to bump my set temp on the PID to 162F. Once I did that, it stayed right at 155F in the mash tun.

It does make sense to me, since the temp sensor is reading the temp of the water immediately after the heating element, so with that small amount of water running through the rims tube, it heats very quickly. The problem is of course, the temp of the mash tun water is not at my target.

A couple of background notes:
* I did verify accuracy of my temp sensor (rtd 100) was reading 32F in ice water.
* I did verify accuracy of the Brewmometer with another thermometer.
* This test is being done indoors at 69F, so heat loss should be minimal.
* I'm using a 5,500W 240V heating element wired at 120V, so 1,325W effective.

Is this typical?

Should I just plan on setting my PID target temp 7F higher than I want?

Thanks,

Allen

 

[IndyBlueprints]

Well, I spoke too soon. The Blichmann Brewmometer in my mash tun is several years old. The Brewmometer in my brew kettle is new. I transferred this test water into my brew kettle, and at 155F on the PID, the Brewmometer reads a fairly consistent 156-157F.

What the heck?

I'm guessing this is fairly typical???

 

[BrunDog]

Yes, a roughly two degree difference between the RIMS probe and the tun probe is typical, depending on flow fate and ambient conditions.

 

[rudylyon57]

Yes, a roughly two degree difference between the RIMS probe and the tun probe is typical, depending on flow fate and ambient conditions.

With a similar setup & power as the OP, I needed a 2-3F offset on my PID setup to get the set point to more closely match the actual mash temp. That was under what I would call typical mash flow rates. Agree with BrunDog that the correction/offset needed will depend on flow rate, It will also depend somewhat on where in the MT you measure. In my case, I measured a few locations and took an average.

 

[IndyBlueprints]

Pretty much got it dialed in. I was able to adjust the set screw on the older Brewmometer to get it close to right. Not exact, but close enough to use on my HLT.

BTW BrunDog, thought you'd appreciate a picture of my Brewing Partner, Jenny!

 

[BrunDog]

Look at that face!! How old... young yeah?

 

[IndyBlueprints]

Yep, she just turned 3.

 

[BrunDog]

Beautiful! Such great dogs - I swear they can look into your soul.

 

[JBiermann]

dont forget the offset feature in your pid to dial in digital temp to the analog

 

[IndyBlueprints]

dont forget the offset feature in your pid to dial in digital temp to the analog

I did not adjust my PID offset, since it read right at 32ºF in ice water. I don't trust checking it with boiling water, because I'm not convinced just because water is boiling, doesn't mean it's not higher that 212ºF.

Thoughts?

 

[Turkeyshot]

I did not adjust my PID offset, since it read right at 32ºF in ice water. I don't trust checking it with boiling water, because I'm not convinced just because water is boiling, doesn't mean it's not higher that 212ºF.

I don't believe water temp could get over 212 degrees unless it was under pressure. Because otherwise it would turn to steam.

 

[augiedoggy]

I did not adjust my PID offset, since it read right at 32ºF in ice water. I don't trust checking it with boiling water, because I'm not convinced just because water is boiling, doesn't mean it's not higher that 212ºF.

Thoughts?

I thought it was already covered but its normal. The temperature changes from one temp sensor/probe to another because of normal temp losses due to the cooling effect of the wort traveling through a silicone line in a much cooler room as well as temp losses from the mashtun walls being cooler for the same reason. therefore the temp will always be off a degree or more depending on ambient room temps and flow speed. those that claim there is no difference do not have their two temp measuring devices calibrated to each other.

when I want to mash at 154 I set my rims pid so 155. in the winter when it much cooler in my brew room I have to set it to 156 and maybe even 157 if its cold enough due to my brew room having no heat vents. simply put the wort lines to and from as well as the mashtun itself are acting as a very poor heat exchanger and and they start cooling the wort as soon as it leaves the rims or herms.

Now if your rims tube is too short or the flow is too fast so the transfer from the heating element to the wort isnt complete and even than you can get wort exiting the rims with constantly fluctuating temps to begin with... That another issue all together you fix with either a longer rims tube and element or better mixing up of the wort in the rims, or slower flow for more contact time with the element.

Also from what Ive been told your boiling point depends on your altitude but pure water cannot go over 212 degrees... It turns to steam vapor after that. so if your temp probe is reading above that it needs to be recalibrated. However these probes are not perfect... They might read perfect at one end of the temp spectrum and not at the other... Thankfully for what they are being used for here it really is a non issue since they wont be out enough to have any effect on anything but the temperament of an OCD mind.

 

[IndyBlueprints]

I don't believe water temp could get over 212 degrees unless it was under pressure. Because otherwise it would turn to steam.

Thanks Turkey & Augie.

 

[mabrungard]

You are far better off calibrating your thermometers at boiling than freezing. The first thing to recognize is that the boiling point in Indy is 210.5F. It's not 212F. Since a typical mashing temp is in the 150F range, its only about 60F from boiling point, but over a hundred degrees from freezing. The boiling point is closer to your temperature of interest and is more reliable.

The best thing would be to calibrate your instruments with a certified thermometer at around 150F. Foam Blowers members have access to a certified thermometer.

 

[IndyBlueprints]

Great information Martin, thanks.

I really should start going to the FBI meetings.

 

[mabrungard]

First Wednesday of the month at 7pm at Triton Brewing.