Boil Pulsing -PID in Manual Mode

[thomasjr16]

I have a 3 vessel setup with a single PID controller that runs my HLT during my mash then I switch over to manual mode on the PID to run the boil kettle.

I've autotuned the PID, using the HLT, and checked the PID temp with my pocket digital thermometer to verify that my PID and trusty thermometer read the same.

I've brewed twice on this setup, hit my gravities, made good tasting beer, but experienced this odd pulsing boil (element on =boil, element off = no boil). Both times I switch the PID over to manual mode and run around 67%.

I'm new to electric brewing, but shouldn't the boil be smooth? Since my temps in the HLT are correct in auto mode after the autotune I didn't want to go messing with the P, I, and D settings if others have the same experience.

Thanks for any insight

 

[augiedoggy]

It would help if we knew what make and model pid your using and how your confirming its in manual mode because from what your describing the pid is in fact NOT in manual mode or the manual mode doesnt work on your pid...

 

[ajdelange]

A PID controller with PWM output in manual mode turns the output on and off according to what percentage of full output you request. Suppose you have set up a cycle type of 100 seconds. If you request 10% output the controller will turn the output ON for 10 seconds and leave it off for 90. If you request 90% output the controller will apply power for 90 seconds and stay off for 10. You should be able to verify this by looking at the trigger light on the SSR or the controller itself. What you see is quite normal. If it bothers you reduce the cycle time.

 

[thomasjr16]

Gotcha... I'm using an Auber 2352 PID and hit the A/M button to go from auto to manual. I then program the PID to 100% until hot break then back down to 67%ish

On a side note, my thermometer is always in the HLT but swap out element cables depending on needing the BK or HLT

 

[thomasjr16]

A PID controller with PWM output in manual mode turns the output on and off according to what percentage of full output you request. Suppose you have set up a cycle type of 100 seconds. If you request 10% output the controller will turn the output ON for 10 seconds and leave it off for 90. If you request 90% output the controller will apply power for 90 seconds and stay off for 10. You should be able to verify this by looking at the trigger light on the SSR or the controller itself. What you see is quite normal. If it bothers you reduce the cycle time.

I read somewhere about reducing the cycle time to something like 2 or 3 seconds to smoothen out the boil as it would fire on and off much faster but wasn't sure if others experience the same kind of pulsing.

I'm of the mind set that it it works, don't change it but I only have two ebrews under my belt and thought others might know of a setting that I may have to change on the PID.

I guess by changing the cycle time I would probably have to auto it again, right? I actually just did that and the temp reading from the HLT just jumped up to a really high number. I'm currently in manual mode on the BK as if boiling.

 

[augiedoggy]

yes you have to shorten the cycle time... I use mypins and the cycle time is already shortened by default... at 67% its on for 67% of each second so the boil is smooth.

 

[orangehero]

Change the "P" and "t" values to 1.

The 2352 is a bit strange, depending on what the P, I, and D values are the t is affected. Even when everything is set up right and t is at the apparently lowest value of 2 it will still make a pulsing boil and in some cases cycles longer than the nominal 2 seconds. I have also found that after running autotune for certain P, I, and D values changing the t back down to the lowest value will create an error with the PV (temp reading) where it shows some nonsensical value. It's best to have a dedicated one for the BK where you don't need the highest precision when in automatic mode, for example doing a hop stand.

 

[The10mmKid]

Auber doesn't mention cycle time as related to manual mode. I don't own one so I cannot verify this is a valid setting during this mode. I'm inclined to think it doesn't.

OP with your stated setting of 67%, would you say the element is on for 40sec(67%) and then off for 20sec(33%) of a minute?

'da Kid

 

[ajdelange]

No, don't retune. Tuning doesn't apply to manual mode. Just go through the menu until you get to the 't' parameter. Set that to a lower value but remember if you set it too low the element won't have time to get up to temperature before it goes off again. Don't forget to set it back to what it was (as determined by autotune) when you do use it in PID mode.

 

[orangehero]

It will noticeably pulse unless P is 1 and t can be lowered to 1 as well.

 

[LandoLincoln]

Is pulsing an actual problem? How cold is your wort going to get when it's not boiling vigorously? 211.5 degrees? You may be trying to fix something that isn't really a problem. But if you like to see a nice even boil go ahead and mess with the settings.

 

[ajdelange]

I'm just going by the manual and beyond that assuming the thing is a normal controller. Manual says quite clearly in 2 places that the minimum for t is 2. It also says in manual mode that the RTD input is not considered in manual mode and as P is sort of like the 'proportional band' (it isn't because this is a fuzzy logic controller) it should have no role in manual mode.

 

[orangehero]

That is what you would expect from reading the manual but in practice the 2352 software behaves differently. Like I mentioned previously, I've tried running autotune with mine several times and the t is usually set to some high value, say 14. Occasionally the autotuned PID values that it comes up with are such that if you try changing the t back to 2 it will reveal a bug in the temperature reading.

Depending on how large your kettle is the pulsing can be a problem as it can be quite violent.

 

[Bobby_M]

The minimum cycle time on the Auber is 2 seconds so at 50% power, it will pulse on for one full second and off for one full second. The only way I'm aware of to get shorter (and even MUCH shorter cycles) is to layer on the Auber Power Regulator which can slice down to 1/60th of a second.

 

[orangehero]

Even at t=2 it can still cycle longer if P isn't 1.

https://www.homebrewtalk.com/showthread.php?t=249312

 

[thomasjr16]

Thanks guys, I really appreciate the quick feedback and insight.

I'll change a few settings as suggested and run everything again when i get another spare hour or so in the next few days but for the time being, I'm with "landolincoln" in that the pulsing can't really affect much if anything. If a smooth boil cannot be achieved, I'm sure the pulsing is only cosmetic and not a functional issue in the "big picture"

 

[Bobby_M]

I don't think the P setting has influence in manual mode.

 

[augiedoggy]

The minimum cycle time on the Auber is 2 seconds so at 50% power, it will pulse on for one full second and off for one full second. The only way I'm aware of to get shorter (and even MUCH shorter cycles) is to layer on the Auber Power Regulator which can slice down to 1/60th of a second.

Or replace it with one $25 mypin td4