AHB Wiki: PID and On/Off Control Basics

[Adr_0]

Hi all,

Check out the attached Wiki for an intro to On/Off and PID control, including:

• Plusses and minuses of each type and which applications are best for which
• Example system configurations (1V, HERMS, RIMS) and recommended controller types and sizing
• Controller hookup
• Basic controller settings

Probably too much information, but let me know if it's good, bad or ugly.

Cheers,

Adr_0

View attachment PIDWiki_rev0.pdf

 

[nosco]

Thanks Adr_0. Ill be giving that a read asap. It looks VERY detailed

 

[Adr_0]

The 'Example 2' - which is HERMS with a controller in the HEX/HLT - can work very well if you pre-set it to 70°C, so do your strike water and initial ramp, BUT you need to manually reduce this setpoint down to 0.5-1.5°C above your target rest temperature a couple of degrees before you get there to avoid overshoot. So there's a bit of manual intervention, but technically this will give you very good response on a 3600W, 50L HEX, 50L mash, 12-16m coil system.

You can do the same with Example 3, or the coil return temperature control, but it's a little riskier - much more likely to get overshoot.

Small HEX's with a short coil are probably the best, but not the most convenient if you want a combination system.

Many ways to skin a cat...

 

[Adr_0]

I can explain the Integral thing - why it causes overshoot, so don't use it at all - but it's a bit much for a Wiki.

If your system is designed well, all you should need is P control. If you need a bit of D that's ok, I will provide a bit more im Part II...

 

[Nullnvoid]

Awesome, I will be reading this. I won an PID but haven't worked out how to use it. This might give me the answer I need!

 

[GibboQLD]

There's a good write-up about PID tuning WRT: brewing on this site, if it helps.

 

[Adr_0]

Rev 1:
View attachment PIDWiki_rev1.pdf
- Corrected the PID reference to PD for the Example 1/1V systems
- Added the temporary setpoint to preheat for Example2/HEX control system

 

[Adr_0]

There's a good write-up about PID tuning WRT: brewing on this site, if it helps.

It's a very good writeup indeed, going into a lot of detail about PID control.

Unfortunately the example system in his diagram is a self-regulating system, whereas a HEX, HLT and Mash Tun are all non-self-regulating systems - case in point:
- Set your element to manual, 50% (e.g. 1800W on a 3600W element) on your nearest HLT/1V system
- Record the temperature it settles out at....
-....which it doesn't.

Changing the output/element power only really changes the slope of the temperature change, which needs a completely different approach - hence me blabbing on about absolutely avoiding using Integral control.

EDIT: Looking at his results, it's oscillating pretty badly for a lot of effort into tuning the PID. The P, I and D are all fighting each other. My RIMS system uses P only, and holds the setpoint superbly with no overshoot.

 

[Adr_0]

Check out the next chapter, on PID tuning. This also captures the 'nature' of homebrewing vessels and why they can't be treated like traditional systems.

http://aussiehomebrewer.com/topic/93940-ahb-wiki-pid-tuning/?p=1431812