Herms/rims Temp Control No Pid

[Blackened]

Hey all,

As my RIMS is progressing nicely (bought most of the bits but un-assembled), I'm turning my attention towards thoughts on controlling the output temperature of the heat tube.

I intend to place two temperature probes. One on the inlet and one on the outlet. I intend to program my controller (a Maximite compatible Duinomite Mega) to compare input and output temps, and rather than an on/off action use PWM to reduce power as needed.

Provided I don't vary the flow, the controller should predict the output temp, based on the input temp + gain (as previously measured), and be able to reduce the power to maintain the output temp with minimal over/undershoot. At least, that's the plan at the moment!

Anyone have any thoughts on this approach? Tried it and succeeded or failed?

Cheers

 

[Yob]

dont know if the info is in there for you (Im a HERMS man) but there is THIS thread

:icon_cheers:

 

[Thirsty Boy]

i have no opinion (due to lack of expertise) on the way your chosen form of control will work - but i can tell you that an assumption that your flow will not change, is not necessarily true.

As the mash progresses, proteins break down, starches convert to dextrins, dextrins convert to sugars and things get hotter etc etc the viscosity of the wort changes as does the physical structure of the grain bed. All of which means that your flow rate may well not be, and in fact probably wont be, consistent over the entirety of the mash.

So if your control paradigm is overly sensitive to flow rate, then it might not be appropriate, or you will need to put in place a flow meter of some kind so you can monitor and adjust as required.

As i said, i dont know if this sort of measure and control system is a "good" one or not - just making sure you know what you are dealing with.

 

[raven19]

I previously undertook a few comparisons between mash temp and RIMS tube outlet temps here (a few pages into the build thread):
Post 62 - http://www.aussiehomebrewer.com/forum/inde...44730&st=60

The hottest point in the system is going to be directly downstream from the heating element, so that is where my temperature probe is for my system.

I would suggest you are possibly overcomplicating things looking for a relationship between inlet & outlet temps due to the number of variables Thirsty Boy outlined above (noting also the possiblity of stuck mashes if brewing a wheat, etc). However I know nothing of the Maximate controller, so you could be onto a winner. Keep us posted!

 

[Blackened]

Hey Thirsty,
Thanks for the input. I intend to measure the gain on-the-fly and average the last few readings to get the actual gain based on the flow rate at any given point during the mash. If the flow changes this will be reflected in the gain and power altered accordingly. In theory of course. I have some of the algorithm worked out in my head but have yet to sit down and put it into code. I think I should get some sort of flow sensor though, so I can detect flow rates that are out of bounds and trigger an alarm or something.

i have no opinion (due to lack of expertise) on the way your chosen form of control will work - but i can tell you that an assumption that your flow will not change, is not necessarily true.

As the mash progresses, proteins break down, starches convert to dextrins, dextrins convert to sugars and things get hotter etc etc the viscosity of the wort changes as does the physical structure of the grain bed. All of which means that your flow rate may well not be, and in fact probably wont be, consistent over the entirety of the mash.

So if your control paradigm is overly sensitive to flow rate, then it might not be appropriate, or you will need to put in place a flow meter of some kind so you can monitor and adjust as required.

As i said, i dont know if this sort of measure and control system is a "good" one or not - just making sure you know what you are dealing with.

 

[Blackened]

Hey Raven,
Thanks mate. Over complicated? Well yeah of course!! Many would say the same about RIMS/HERMS full stop! Lol
I'll post a link to Maximite later if I remember. It's a mini computer with IO ports, keyboard input and monitor output. It runs a programming language called MMBasic and your imagination is the limit basically. The arduino is similar-ish.

I previously undertook a few comparisons between mash temp and RIMS tube outlet temps here (a few pages into the build thread):
Post 62 - http://www.aussiehomebrewer.com/forum/inde...44730&st=60

The hottest point in the system is going to be directly downstream from the heating element, so that is where my temperature probe is for my system.

I would suggest you are possibly overcomplicating things looking for a relationship between inlet & outlet temps due to the number of variables Thirsty Boy outlined above (noting also the possiblity of stuck mashes if brewing a wheat, etc). However I know nothing of the Maximate controller, so you could be onto a winner. Keep us posted!

 

[raven19]

Overcomplicating things is what we brewers do best!