PID Controllers

[blades&grace]

I know there's some info on the forum about building HT ovens. My question is....Does anyone have an opinion on which is the best PID controller to go with? I purchased the least expensive one I could find on eBay and it lasted all but a year! I want to replace it with something more reliable. Any thoughts?

Brent Cramer

 

[Nathan the Machinist]

My furnace came with a Eurotherm 2416. I've had years of very precise trouble free service from it. They list for close to a grand, but I see a used one went on eBay for $67. It has ramp and dwell, which might help you normalize your cooked blades. My furnace heats up to ausentizing temperature in a few minuets, and it doesn't over shoot by more than a couple degrees. Once to temp, it stays parked within one degree. I like this controller.

I picked up an OGDEN on ebay for pretty cheep once. Didn't use in in a furnace though. It was inexpensive, probably $20 (they list for 200-300), but it would probably do better than the Chinese one you had trouble with. It was hefty enough I was able to wire the heaters directly through it without a relay. Probably about 1000 watts like that.

 

[micad]

Brent,

While this does not directly address your question..........

It seems to me that your controller should have lasted far longer than a year. The one I'm using has been going strong for nearly 15 years now and no problems.
When you wired it did you use the controller contacts to directly control the heating elements?
If so, that may explain the short life. These contacts are not generally rated to handle much current.
The controller should only be used to turn a relay on/off. (This relay needs to be rated for at least the current demands of the heating elements). The relay controls the power output to the elements.
Even if your controller is rated to handle a heavy (amp) load it is better to use an auxilary relay for this to maximize the life of the controller. Relays are cheaper than controllers.

Just a thought....

-Mike-

 

[blades&grace]

Thanks Mike for your response.
No the controller was connected to a relay. I thought at first that the mechanical relay had just burned out, but after getting some help replacing it with an ssr I found that my controller opens and closes at temps less than 999C but stays on at temps over!!!! It was not a problem before; like I said I have heat treated many blades with it in the last year so I'm not sure what happened. Any thoughts?