Temperature offset

[timweber]

I have a probe a the outlet of my mashtun. It reads about 2 degrees low from the center of the mash due to heat loss. Is there a way to set an artificial offset for this probe? Or do I have to run though the calibration proceedures.

[ECC]

Sure, just generate new coefficients based on the new temperature.

Here are the directions for calibration. http://forum.embeddedcontrolconcepts.co ... p?f=6&t=10
The default coefficients use these values, which are temp/resistance measurements at 3 points:
degF Resistance(ohms)
32 29481
104 5595
158 1991

Simply bump up all temp readings by 2deg and recalculate:
34 29481
106 5595
160 1991
Which yields
A: 0.0010280701
B: 2.38264E-4
C: 1.5228655E-7

Program these new coefficients into the system settings page for your temp probe and you should be good to go.

[ldo2626]

This may be what I am experiencing as well, but not sure. Please excuse my ignorance... I only have one AG batch under my belt.

I have my RIMS heater associated with my RIMS out probe (positioned immediately after the heating element). So I have to assume if I set it at 155 then the water hitting the grain bed is 155. At the MLT outlet (pump entry) I also have a temperature probe and this one reads 5 or so degrees lower than the setting at the RIMS outlet. Common sense says this is normal due to heat loss, but how should I set it? What is the proper way to maintain my mash temperature?

Thanks

[ECC]

Yeah, this is a hard problem. I'm really not a big fan of adjusting your probe's offset to account for the heat lost in transit. I think it works, if you can say with absolute certainty that its always constant. The probe is reading correctly, its the system that is losing heat. I think you have a few options here, although there are not any clear answers. I think having a second probe in the mash is a must, just so that you know where you are.

1. Find the difference, and bump the offset of the probe of the RIMS outlet. Not ideal as I mentioned above, because the offset could change, and the probe now has a fixed error.
2. Leave the probe offsets alone, but mentally add a few degrees to the setpoint to make up for the heat lost. When mashing, verify the mash temp and adjust the setpoint as needed.
3. Change the temperature probe association to use the mash temp for PID control. Tune the PID such that you get acceptable overshoots and system response time. This has the risk of ruining a few batches of beer, because you can't tune it with water. A big beer might have different characteristics than a small beer, so this might take some trial and error.
4. Fix the system, insulate. Minimize any temperature lost, so that the difference of the RIMS outlet and mash are as close as possible

3 is ideal, but you won't find too many people willing to risk multiple batches to get it right. Personally, I do a combination of 2 and 4. Most brewers will tell you to keep the probe at the RIMS outlet doing the work.

[clegg]

I'm also interested in this topic.

If you did have a second temperature probe in the mash tun, how would you setup the BCS to leverage it to address the temperature offset? Is there programming logic that would allow you to still use PID control at your RIMS tube outlet temp probe, while having a temperature setpoint based upon the mash tun temp probe?

Can you code BCS to calculate the delta between the two probes and add it to the setpoint for the RIMS temp probe? Is there an example system / code somewhere?

[ldo2626]

Thanks for the responses. I hope I didn't hijack this thread. I think I am going to use a combination of 2 and 4 as well. Educating me about the mash may help also. What is second best to getting an ideal mash temp ("ideal" being holding the constant temp throughout the mash)?

A) Overshoot the RIMS temp so it exits the mash tun while recirculating at my desired mash temp?
B) Set the RIMS temp at my desired mash temp and leave it (regardless of the fact that it is exiting the mash tun at a lower temp)?
C) Try to find that happy medium where RIMS temp is over my desired mash temp but exit temp is below?

Thanks again.

[ECC]

Can you code BCS to calculate the delta between the two probes and add it to the setpoint for the RIMS temp probe? Is there an example system / code somewhere?

If you calculate the delta and change the setpoint of the RIMS probe, you are effectively using the Mash probe. If you think about it, the reason that you want to use the RIMS outlet is to get around big overshoots. This is when the Mash probe is continuously calling for more heat, even though there may be enough heat in the Mash tun, however it hasn't settled down to the probe. By the time the Mash probe sees that it has enough heat, its too late because the RIMS was on for too long, and then you get a big overshoot. By using the RIMS probe you are limiting the maximum temp out.

C) Try to find that happy medium where RIMS temp is over my desired mash temp but exit temp is below?

ldo2626, I would say C).. But I'm no expert, I'd love to hear other opinions.

[ECC]

How about a mode that does the average of the 2 temps? Seems like that would be a simple solution that would make it more automatic. I think it gives us what we want. It would limit the overshoot, while maintaining the average temperature of the grainbed. You still might get a little overshoot due to the Mash temp pulling the average low. But it seems like a fun option to play with.

By enabling Temp0/1 averaging, Temp0 becomes the average of temp0 and temp1, and temp1 is unchanged (still temp1). You could then use temp0 for the PID association and place it on the RIMS outlet.

Would there be any other averaging combinations that would be useful? I could see a 3way average. Or 2x 2ways.

[Yorg]

Isn't the ability to anticipate lag in your system exactly what PID is good at?
While an offset may be desirable to cater for the loss from the RIMS tube to the mash, the PID should be able to cater for overshoot, right?

[ECC]

Yep, definitely an option.

• 3. Change the temperature probe association to use the mash temp for PID control. Tune the PID such that you get acceptable overshoots and system response time. This has the risk of ruining a few batches of beer, because you can't tune it with water. A big beer might have different characteristics than a small beer, so this might take some trial and error.

3 is ideal, but you won't find too many people willing to risk multiple batches to get it right. Personally, I do a combination of 2 and 4. Most brewers will tell you to keep the probe at the RIMS outlet doing the work.