One PID or two?

[P-Lay]

After reading through the thread titled "My Rims Job", I have been thinking about PID's. In that thread, it was discussed that the temperature probe should be placed as close to the heat source as possible so you don't overheat your wort. On that system, a Brew-Magic clone, there were two heat sources - 1) from the burner under the MLT; and 2) from the RIMS heating element.

I was wondering why you couldn't use both heat sources/temperature probes in one PID. I did some searching and found some dual-loop PID's that were for heating/cooling combined, but not for multiple heating sources. Is this possible?

If not, would it be feasible to use two seperate PID's running at the same time? One for each heat source, each with common (or similar) goals - to get the wort up to temp and keep it there. You wouldn't have to have each maintaining temperature the whole time. E.g; with both running at the same time, the burner loop could be set to raise the temp until about 5-10 degrees below desired wort temp and then shut off and let the RIMS loop continue heating until desired wort temp and then just maintain after that.

Based on the video from Sabco, it showed their control system notifying the user to manually turn on and off the burner. I am thinking of a way around that is all.

Any thoughts? Ideas?

 

[Sawdustguy]

You can absolutely use 2 PID's with 2 separate temperature sensors to control 2 heat sources. I use 2 of them, one to control the HLT temperature and one to control the RIMS heater. I don't understand why you need to control the MLT burner if you use the RIMS heater to control the mash temperature. The mash should be at temperature when you add your strike water. All the RIMS heater does is keep it at temperature while recirculating. Why would you need to control the MLT also? See https://www.homebrewtalk.com/f51/rims-dummies-114997/

 

[Sawdustguy]

You could use the MLT burner to assist the RIMS heater but all you would have to do it watch the RIMS heater PID until it was up to temperature then turn the MLT burner off.

 

[P-Lay]

You can absolutely use 2 PID's with 2 separate temperature sensors to control 2 heat sources. I use 2 of them, one to control the HLT temperature and one to control the RIMS heater. I don't understand why you need to control the MLT burner if you use the RIMS heater to control the mash temperature. The mash should be at temperature when you add your strike water. All the RIMS heater does is keep it at temperature while recirculating. Why would you need to control the MLT also? See https://www.homebrewtalk.com/f51/rims-dummies-114997/

I read that RIMS info already, it was good info... thanks. If I decide to build a RIMS system, I'll definitely do something similar.

What I was thinking with the dual heat sources on the MLT could be for step mashes. You could decrease the time between steps with assistance from the burner without adding any water from the HLT. Or, if you wanted to preheat the strike water in the MLT, bypassing the HLT, it could be useful. Still learning about the process so please bear with me.

My main question was about the one PID controlling both of the heating elements. Is that possible? Is there such a thing? Not that I think it's necessary, but I like to tinker and this might be fun.

 

[Sawdustguy]

I read that RIMS info already, it was good info... thanks. If I decide to build a RIMS system, I'll definitely do something similar.

What I was thinking with the dual heat sources on the MLT could be for step mashes. You could decrease the time between steps with assistance from the burner without adding any water from the HLT. Or, if you wanted to preheat the strike water in the MLT, bypassing the HLT, it could be useful. Still learning about the process so please bear with me.

My main question was about the one PID controlling both of the heating elements. Is that possible? Is there such a thing? Not that I think it's necessary, but I like to tinker and this might be fun.

I see. There are a host of multiple independant loop PID's on the market. They tend to be very expensive though. It may be less expensive to use two separate PID's. You need two separate temperature sensors. If you use a single loop PID, once you break the loop, you loose your control. If you figure a way to do it with a single PID please let me know how you did it.