temp pid

[Joe G]

I'm looking at getting a temperature pid controler but have never used one. It'll be used to keep an oven at a temp of 250F , the heating element is actually a large hot plate. I need the oven to get to 250F and then have a timer for 15 minutes, then I'll be opening the oven up to reclean/check the parts and if all is well, close the door and have it 'bake' for exactly 2hours at 250F. what would be a good cheap controller that would be able to do this with a buzzer or indicator of some sort for the times? I could also make a timer for the buzzer if needed. thanks

 

[KeepItSimpleStupid]

What kind of wattage/voltage are we looking at?

There was a thread recently that referenced a Toaster oven controller for PCB work that might be able to work for you.

PID is one thing, and output type is another. Some output types:
a) Relay - ON/OFF control
b) Slow cycle triac - (a) using a triac
c) ZCP - Zero Crossing Pulse - changes the number of AC cycles
d) PAF - Phase Angle Fire
.........a) With current limit
..........b) Without

The temperature sensor is yet another item that has to be selected and/or programmed.

PID now is mostly done in software rather than a pure hardware implementation. I've programmed a PID algorithm in software without auto-tuning.

Without knowing a little more, like the mass of the object and the heating element size. I can't recommend much. The PAF output device is the best. Current limit is REQUIRED if doing an inductive load.

As usual, these things get mushed together: controller, programmer, and the power controller.

I'm used to using industrial controller with multiple recipies and at least two parts. The controller spit out something like 4-20 mA, which the end device acted on.

Aside: I've also used separate programmers. One was really cool for it's time. You used a styles and broke a piece of foil into two non conductive pieces The pieces were fed with low level AC 180 degrees apart and the sensor looked for the null. Way cool for like the 1970-1980 technology.

Depending on how often and how accurate things have to be, you need to pick a full automated controller or can you get away with timers? Since it won't cool completely after 2 hours, you probably have to remove it?

I suspect that your going to attach to the element of the heating plate directly? So, again, you have to find a sensor - a K type thermocouple would work.

You also have to decide if over temperature protection is in the cards.

One way to do "programming" is to use a controller with say an INT/EXT analog input. When I had these, I would wire external two switches: On/OFF and EXT/INT. That does provide an easy way of turning things off 0 C or F setpoint, turns it off.

Other times, that same switch was wired to a definite purpose contractor so the switches worked as above. This would also isolate the load. It was also attached to a dedicated over temperature monitor. In some cases, I used yet another switch and some relay logic to enable auto drop-out or what to do in case of a power failure.

I did present a bit much of stuff. In some cases, you could send the programs over RS232 or RS485 instead of doing it manually.

None of these options were cheap.

 

[Mosaic]

over the counter:
https://www.amazon.com/JLD634-Setpo...&qid=1393809132&sr=8-1&keywords=ramp+and+soak

To build one as a microcontroller DIY would prob run u about 20 bux including an SSR.

 

[Joe G]

thanks both of you. the v/a =120vac, <10amps . The temp measured would be the atmosphere in the oven (like a kiln). I was thinking of using a solid state relay to control the on/off of the 120V heater element. Once the 2hrs are met, the parts are taken out to cool and the oven would be turned off or a new loading cycle would start. Its actually for a prototype of metal finishing for a friend. Rite now they watch the temp and the time with a watch......very lame and time consuming, so I thought of doing this for them.

 

[Mosaic]

Well here's a DIY for u:
https://www.jameco.com/webapp/wcs/s...001&productId=2190178&catalogId=10001&CID=CLO

 

[Joe G]

I'm kicking around at using a pic.......I'll let you's know how I do if I go for it. Looks like Ill be doing abit of learning again been wanting to try it so now I think I have a reason to give it a whirl ps thanks for the link to get me started.

 

[Mosaic]

I used AN964 for the PIC last time I did PID. The flowchart is a good guide for doing the programming.

 

[Joe G]

thanks I had an937 saved already, I'll give that one a go.

 

[KeepItSimpleStupid]

This http://www.zallus.com/msp430-reflow-oven-kit/ was the kit that was discovered on another thread.

Just noticed that it's a fixed profile (actually 2 profiles), but the source code is available.

 

[Joe G]

thanks KISS, found it, that may help alot