PID troubles

[jedheuer]

Hey all,

I am having troubles maintaining mash temperatures with my PID controller.

I put links to the actual PID and probe that I am using below. My set up is that I have the probe in a tee coming out of the mash tun so i am essentially monitoring the temp of the wort coming out of the mash tun (not the mash bed itself). I have a march pump hooked up to the PID so it will kick on to recirculate as needed to maintain temp. I have a coil in my HLT were I keep the temp around 170. I have autotuned with my setup.


Now the problem I am having is that the PID says that it is maintaining a stead mash temp of 149, but when I stick the probe in the mash bed the temp keeps creeping up ( 150, 151, 152, etc.) but my PID keeps reading 149. What could be going on here? Is the probe cooling too much in the tee? Should i get a larger probe and stick it in the actual mash bed?

Any help appreciated... and thanks!





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[poislb]

Have you tried putting the PID after the ball valve outlet on the pump with a tee instead of off the mash tun?

Have any pics of your set up?

 

[DanH]

I think the norm is to put the probe somewhere where you can measure the temp of the water as it enters the MLT while recirculating (like near the outlet of a RIMs tube).

 

[jeffmeh]

Or constantly recirculate the wort through the HERMS coil, constantly recirculate within the HLT, and use the PID to keep your HLT at mash temp, placing the probe in a T in the HLT recirculation loop. I know that's a different configuration, but it avoids recirculating wort through higher temps in the HLT that can denature enzymes.

 

[jedheuer]

Or constantly recirculate the wort through the HERMS coil, constantly recirculate within the HLT, and use the PID to keep your HLT at mash temp, placing the probe in a T in the HLT recirculation loop. I know that's a different configuration, but it avoids recirculating wort through higher temps in the HLT that can denature enzymes.

Yea, I had this configuration as well and it ran cold, but said that it was at the proper temp. so i am wondering if i have a faulty PID or if its not configured right.

What would cause the PID to read a constant temp but actually continue to go up several degrees over time?

 

[kenh]

Yea, I had this configuration as well and it ran cold, but said that it was at the proper temp. so i am wondering if i have a faulty PID or if its not configured right.

What would cause the PID to read a constant temp but actually continue to go up several degrees over time?

Where is the probe in relation to the temperature sensor feeding the PID?

Are you continuously recirculating wort though your mash tun?

 

[jeffmeh]

Have you calibrated the temp probe against a lab-grade thermometer, and set the appropriate offset in the PID?

 

[jedheuer]

Where is the probe in relation to the temperature sensor feeding the PID?

Are you continuously recirculating wort though your mash tun?

The "probe" would be just me checking in the actual mash bed with my hand held thermometor which i calibrated my PID to match. But no, I am not conitualy recirculating. I have a coil in my HLT (about 170) and the march pump turns on and off to keep the temp correct.

 

[kenh]

The "probe" would be just me checking in the actual mash bed with my hand held thermometor which i calibrated my PID to match. But no, I am not conitualy recirculating. I have a coil in my HLT (about 170) and the march pump turns on and off to keep the temp correct.

You can't keep you mash at a constant temperature without recirculation. Even thin mash is too thick and the temperature will always be higher near the element.

 

[jedheuer]

You can't keep you mash at a constant temperature without recirculation. Even thin mash is too thick and the temperature will always be higher near the element.

Thanks for the reply. You are correct, i think the only way to maintain a constant temp is to have a constant recirc going on. other wise the hotter wort will eventually build up on top of the mash bed.