attn PID controller users

[pensrock]

Hi, I am in the process of designing and building a PID controller. It will be a little different than most here but since I have not made anything yet I was wondering if any of the users have any wishes that they would have liked to include in the PID controller they have now. I am going to be using a Honeywell 1/4 DIN controller that I picked up  for free and also plan to add a timer to shut the control signal to the SSR off when it times out. That way I can set the heat time to whatever I want and it will turn itself off for me. I'm thinking about using one of the alarms in the controller to act as an over-temperature function. I can set it at 300 degrees, or whatever I choose, and it will turn the heat off if it ever gets that high. I'm was wondering if you were designing one for yourself, what other possible functions you may want. TIA pensrock

[Arcs_n_Sparks]

pensrock,

Built my PID from scratch (really scratch, microcontroller and my own code), so I have always had an interest in the same question you have posed to the members here. I have collected various comments over the last year or so that relate to your question, so here is what I have. (all relate to the OBS with PID add-on).

1. Some want to turn off the smoke generator off after a period of time (not a PID function, but motivated to save wear and tear)
2. Some want to start at a particular temperature for a period of time, then ramp (up/down) to another temp until meat setpoint is reached.
3. Some want to reach meat setpoint, then hold at temperature.
4. Some want to reach meat setpoint, then hold box at another temperature.
5. Some want to do #4, but hold only for a period of time at the end, then shut off. Indicative that they have drank too much, and forgot about the smoker.   

Arcs_n_Sparks

[Mr Walleye]

Another one I've seen people ask about was for doing sausage. Ramping up a number of times in 10 or so degree increments.

Mike

[Tiny Tim]

I'd like a feature that carries the meat in from the smoker for me when it's done...............

[iceman]

Another one I've seen people ask about was for doing sausage. Ramping up a number of times in 10 or so degree increments.

Mike

That would work perfect for kippered salmon smoking.

[3rensho]

Arcs, what PIC did you use??  I'm just getting into programming these beasties as a hobby and it is really interesting.  Thanks

Tom

[Arcs_n_Sparks]

Used an Atmel ATMega8 (free C compiler integrated into the WinAVR tool chain).

I have played with the PICs, but have not done any serious designs.

Looking at the Cypress PSoC and their PSoC Express design tool (basically, a graphical programming tool that avoids writing code). Very cool. The PSoC chip has substantial an@log capabilities, and can implement capacitive touch sensing to avoid mechanical switches. They have an app note on a PID controller for their chip: http://www.psocdeveloper.com/docs/appnotes/an-mode/detail/an-pointer/an2208.html

The neat part of this implementation is the ability to talk to the chip using your PC and graph the PID performance. You can also tweak the P, I, and D parameters.

Arcs_n_Sparks

[3rensho]

Thanks Arcs,  my aim is to eventually build a device to control temp and humidity in a box for curing salami, etc.  That PID app note looks good.

Tom

[winemakers]

Arc's

you make my head hurt!

 

[pensrock]

Thanks for all the replies. This is the kind of feedback I was hoping for.

1. Some want to turn off the smoke generator off after a period of time (not a PID function, but motivated to save wear and tear)
2. Some want to start at a particular temperature for a period of time, then ramp (up/down) to another temp until meat setpoint is reached.
3. Some want to reach meat setpoint, then hold at temperature.
4. Some want to reach meat setpoint, then hold box at another temperature.
5. Some want to do #4, but hold only for a period of time at the end, then shut off. Indicative that they have drank too much, and forgot about the smoker.

#1 is taken care of with the digital generator but you could probably add a timer to do the same thing.
#2 I think I can do using the temperature controller I am using. I can ramp up or down at whatever rate I choose, deg/min, deg/hr etc. I will need to be at the starting temp then after a period of time actually raise or lower the temp and it will ramp to that point. Maybe not exactly what they asked for but close. We built several basic based computer controlled furnaces that had recipe function in them. You would select a recipe and walk away the furnace would go to a temp, soak for a period then ramp to another temp, soak ramp, soak. you get the idea.
#3 Could probably be done with a dual input controller, one being a meat probe. I'm not sure because I have never tried this.
#4 Possibly the same solution as #3.
#5 if #4 worked you could just use one of the alarm functions to shut down the heat. No matter what the controller would not be cheap and would probably cost as much or more than the smoker itself.

Another one I've seen people ask about was for doing sausage. Ramping up a number of times in 10 or so degree increments.

Mike

This is possible using the right ramp & soak controller. I see Auber now has a Ramp/Soak controller but how well it works and what it's limitations are is unknown. Also the person using it would need to know how to program the controller to do each step. Not difficult for those using them everyday but takes time to learn and understand. My controller unfortunatly does not have the ramp/soak function. 

I'd like a feature that carries the meat in from the smoker for me when it's done...............

Tiny, this is very possible to do..... where do you live?

I'll think these ideas over a little more to see if I can use any of them in my unit using the controller I currently have. I'm looking into the #3,#4 &#5 ideas using the unit I have. I know I can have two inputs but think it is only for a different kind of control, cascading control. Mike's idea is doable but not with my current controller.

Keep the ideas coming!
Thank again.
pensrock