Using the PID function on a Kiln

[CDavisSystems]

     I am working on a large Kiln. We are trying to create recipes for the Kiln to process burn rates. We have many recipes but I can work with that. What we need to do is set the top temp (let say 1800 deg) and have it climb at a certain rate (lets say 300 deg per hour). I have been looking at the PID but I can only see what it can raise strait up to the degree set and stay there but be steady. I would more need to reset the PID after each hour for 6 hours to get it to smooth out but even that would be wrong because it would climb strait to 300 degrees and ride there until the hour was up. We really need it to take the hour to get to 300 degrees, then take an hour to get to 600 degrees and so on until it gets to 1800 deg. Once there we will want it to hold for a time and then descend at a certain rate as well. 

 

     Does anyone have a Kiln program that we can refer to? I can write a real large program that will do this breaking it down to each minute (Like 5 degrees per minute only) but figure there is a better way.

 

     Any help would be appreciated.

[Gabriel Franco]

Can you ramp PID setpoint up at the desired rate? You might need to adjust PID parameters on the road to achieve a better control.

I don't know about kiln process, but used this approach once to control a motor speed.

[Joe Tauser]

You need to make your own ramp and soak generator.  You can set up a data table for your recipes and then store all the beginning and end setpoints in the table, as well as how many hours you want the segment to take.  You can then use a Linearization block to generate a gradually increasing setpoint over time by loading the Y1 and Y2 values with your beginning and end setpoints and increasing the X value with a time incrementing register (you have to make that, too).

 

It sounds more complicated than it is.  Let me know if this makes sense to you.

 

Joe T.

[nax]

Can You send a simple example for that? 

 

Br,

[RBC]

Hi. Thats easy.  Use the step in range function.  I've done it on my fruit dryers i build for the humidity.  You just fill in the steps.  Mine is 5 perc down every time condition met.

 

Works like a charm.

 

2 or 3 rungs and you done.