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Simple PID Controller Setup

03/03/2017 5:53 PM

I have a basic Mypin TA4 PID controller I want to set up to do heating only control cycle work and I can't remember how to set one up for variable control operating conditions any more.

The old controller was a relay output and worked well enough for basic on/off control of a heating element to maintain a temperature but had a fair over and undershoot lag to it of about a 15 degree overshoot (~355 F) once it hit the shutoff point (340 F) . After that on cool down it would have about a 20 degree lag (~320 F) before the temperature started picking back up.

I figure that being the new unit has solid state output I should be able to do on the go PWM of the power in proportion to how far off it is from the setpoint to be more stable and cut down on over and under shoot issue.

The basic numbers are I want to set the temperature for 340 F and have the controller start dropping the power back from 100% down less and less as it reaches 340 F then hold near whatever level it needs to keep it there then start gradually ramping it back up as it drops.

So how do I set this damn thing up to start backing off the heater power as it reaches the programed temperature then start proportionally applying it if it starts to fall off and not have a fit if it has to sit for any period of time with process powered down.

Steady on power level is around 60 - 85% and varies as the incoming product (oil) temperature changes hence not being able to just set the heating element at a fixed power level.

System thermal response time is about 300 F per minute at 100% power and about 100 - 150 F per minute falling.

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#1

Re: Simple PID controller setup.

03/03/2017 8:18 PM
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#2

Re: Simple PID controller setup.

03/03/2017 9:05 PM

Your error feedback is the difference between the actual temperature and your set point (340F). Proportional feedback changes the heater proportional to this error. Integral control changes the heater more and more the longer the error persists (integrates the error). Differential control feeds back due to change in the error.

Here is a tutorial that explains what each control does and how to tune it.

I hope this helps.

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#3

Re: Simple PID controller setup.

03/03/2017 9:19 PM

Unfortunately I have already watched and read all of that.

That initial high level oscillation is the problem.

The units is controlling the oil preheater for my used oil burning boiler and if it gets much over 360 F it starts cokeing up (burning) the contaminants inside the preheater unit until it plugs it or the nozzles up hence the wanting the overshoot part of the cycle cut off.

Right now the all or nothing control works well enough but I was just hoping there a some setting I didn't know about on PID control units for quick ramp up at full power (to say 325F ) followed by a tapering back of power until ~340 F is achieved.

So far with the normal PID setup procedures I seem to be hitting 380 - 400 F peak then dropping to under 300 F (too cool to spray and burn right) low every time then having a damped oscillation down to the range I want that takes about half a normal burner heat cycle to stabilize every time the system fires up.

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#4
In reply to #3

Re: Simple PID controller setup.

03/03/2017 10:43 PM
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#5
In reply to #4

Re: Simple PID controller setup.

03/04/2017 8:22 AM

Unfortunately that doesn't solve the fuel oil preheater overshoot issue which is what I am asking about.

I could do all that stuff you linked to and more with the control system PLR software but it wouldn't serve enough of a gain or purpose to do. I was going to put the fuel oil preheater control on the PLR unit as well but it only has relay outputs which wouldn't have gained me anything over what I have now.

The thing is, I burn used oil which I get for free, 2000+ gallon surplus of it now and I got called to come pick up another 500 - 1000 ASAP, so overall fuel savings are of no issue plus the boiler is located in my new work shed I am setting up where the passive heat loss keeps the place nice and warm in all but the coldest weather.

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#13
In reply to #5

Re: Simple PID controller setup.

03/04/2017 5:03 PM

So tighten up the differential, what's the big deal....I was just thinking you could tweak the nozzle closer to the load on a first stage....or increase the spray pattern width or something....but I know it's hard to think straight when you're freezing your cajones off....

http://www.delavaninc.com/pdf/total_look.pdf

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#14
In reply to #13

Re: Simple PID controller setup.

03/04/2017 6:18 PM

The problem is runing used oil though one of those nozzles requires a bit of cheating to make it work.

Old engine oil is way too thick to pass through them at room temperature let alone at -10 F or worse so it has to be preheated to around 320 F or a bit more to get it's relative viscosity down to where it will atomize right.

Even at that a bit of cheating by raising the pump pressures helps to improve atomization so it's pretty limited on what can be done with nozzle sizing and their pressure/flow rate curves.

As of now I have it set with a .65 GPH 60* nozzle running at ~ 140 PSI which will keep the system running continuously with a water jacket temperature of 180 - 185 F with both the house and shed calling for heat.

Nothing to optimize there being it runs continuously right in the ideal water temp range at full heat load and even if one or both loads are off the ~ 90 gallon water capacity mass gives it enough thermal mass that when the burner comes on it 180F it takes it roughly 15 minutes to warm up to the 195 F shut off point even without any heat load.

Overall the new boiler design does it job well but the preheater that gets the oil up to temperature so it can be ran though a normal fuel oil furnace burner nozzle is the minor grievance.

It worked well enough on the old burner system for about 4 - 5 years in the old boiler system with the simple on/off power control but since the new mini boiler has all solid state control with its PID controller I was hoping to take advantage of it but so far it hasn't shown me any major gains running in PID mode Vs simple on/off mode.

BTW, compared to the old boiler that was physically large (~3 - 4x the external surface area of the new mini unit), and located some 350 feet away in the poorly insulated boiler room off the side of the old shop, the new mini unit being ~ 25 feet from the house plus being in a well insulated building has already cut my used oil consumption in half for the same house heating loads plus gave me a nice comfortable workshed as a secondary effect from its radiant heat loss.

Downside is I am now collecting used oil at a rate that is more than double my annual burn rate so I am going to have to start working on setting up more storage capacity and likely find an alternative use for the excess that's coming in.

I have a used 3000 gallon horizontal diesel fuel tank on legs I picked up a while back but it needs to be cleaned up and worked over to sit as a legless vertical tank before I collect too much more used oil.

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#15
In reply to #14

Re: Simple PID controller setup.

03/04/2017 6:51 PM

What sort of an oil pump are you using?

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#16
In reply to #15

Re: Simple PID controller setup.

03/04/2017 6:58 PM

Standard fuel oil furnace burner and pump system.

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#7
In reply to #3

Re: Simple PID controller setup.

03/04/2017 11:11 AM

Sounds like your derivative term needs some work. Here is a procedure from Omega that seems a good place to start.

Unfortunately, all formulas I have ever tried, only get you in the ballpark. From there you have to experiment to fine tune the loop.

Good Luck!

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#9
In reply to #7

Re: Simple PID controller setup.

03/04/2017 11:49 AM

Thanks!

Well that makes what everyone else seems to feel needs to be a long drawn out overly complicated setup process look way simpler easier to do!

Kind of like most technical work. Why explain and do it simple when you can make it look way way harder and more specialized (expensive) than it really is and needs to be.

I'll give it a go on of these days.

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#6

Re: Simple PID controller setup.

03/04/2017 10:18 AM

Have you considered moving to Florida?

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#8
In reply to #6

Re: Simple PID controller setup.

03/04/2017 11:41 AM

No I have not. I like it here because only the strong, smart and resourceful can survive in this place.

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#10
In reply to #8

Re: Simple PID controller setup.

03/04/2017 1:10 PM

Well, you'd better get that PID working, then. It's winter there, you know, and will be 'til August.

Have you considered using a TMM* controller?

-----

* Tire-Mass Modulation

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#11
In reply to #8

Re: Simple PID controller setup.

03/04/2017 1:18 PM

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#12

Re: Simple PID controller setup.

03/04/2017 3:00 PM

what is the link for the full user manual?

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#17

Re: Simple PID controller setup.

03/04/2017 7:20 PM

The mini boiler. (showing PID overshoot issue with the auto tune settings.)

The controller.

The oil preheater assy.

That's the basics.

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#18

Re: Simple PID controller setup.

03/05/2017 7:06 AM

Are you using the controller's integral function?

If answer is yes, it looks like your controller is over/under shooting due to "integral windup" that will take place while the oil burner is turned off. Disabling the integral function until oil temperature has entered a controllable region should cure the problem.

Zvi

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#19
In reply to #18

Re: Simple PID controller setup.

03/05/2017 10:28 AM

I was not aware of that so I will give it a shot and see what happens.

It does make sense though. Every time it cycles the burner on the PID starts out with wild swings +- ~ 20 - 25F gradually working its way down to a acceptable range, +- ~ 3 - 5F after about 15 minutes which is about the end of the burner run cycle on a short reheat cycle.

That initial over/under shoot is what I am trying to eliminate.

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#20
In reply to #18

Re: Simple PID controller setup.

03/05/2017 9:00 PM

I turned it off and it made the thing way more stable right from the get go on every burner cycle start no matter if it sat for 10 minutes or 3 hours since the last cycle!

Worst over and under shoot at first burner startup is less than 10 degrees with a normal variance of about 4 - 6 after that!

Guess I have to hand out one of my rare actual GA's for GA sake rather than my typical ones I use to counter some fools unjustified OT.

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#22
In reply to #20

Re: Simple PID controller setup.

03/09/2017 4:22 PM

Cool setup, great job! Is the 4-6 variance a constant oscillation from your setpoint during burner operation, or does it reach a steady-state temperature and that is just the variation from run to run?

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#23
In reply to #22

Re: Simple PID controller setup.

03/26/2017 6:10 PM

Pretty constant. It seem to drift a bit up and down from the set point over long boiler running cycles.

It will stay within +- 2 - 3F for a few heating element cycles then start to drift high or low then come back to the +-2 - 3F variation range again.

So far I have not had to clean out the oil preheater due to coking and plugging issues so far so I am considering it good now.

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#21

Re: Simple PID Controller Setup

03/06/2017 12:45 PM
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