help with PID control

[kamenges]

You guys did pick up on the fact that he is dealing with a pair of air-driven process control valves, right? He needs 4-20mA signals going to them. And I suspect his prof. will be REALLY p!$$ed if he changes those valves out for the discrete valves you are talking about.

Keith

 

[Mickey]

You guys did pick up on the fact that he is dealing with a pair of air-driven process control valves, right? He needs 4-20mA signals going to them. And I suspect his prof. will be REALLY p!$$ed if he changes those valves out for the discrete valves you are talking about.

Keith

That's the temperature control. The level control is just a solenoid valve.

Or did I miss something? Show me.

 

[Mickey]

Still working on this. I tried the level control using Mickey's logic and it works, but I had to make the GEQ's into LEQ's since the solenoid is closed when energized. Also it clicks on and off like crazy when the level is on either end of the set point, so I need to add something for it to only energize when it has to change states. When it opens at 55, for it stay open until it goes down to 45 for example. What would I use for that? Thanks again.

Post your program. Zip it first

 

[Mopar5]

That's the temperature control. The level control is just a solenoid valve.

Or did I miss something? Show me.

You're right. The level is controlled by a simple solenoid valve. Temp is with pneumatic valves through a 4-20ma I/P transducer. I'll post the updated zip later, it's on my laptop that I don't have here with me right now.

 

[kamenges]

Originally posted by Mickey:

Or did I miss something?

Nope. You didn't. I did.

Keith

 

[Mopar5]

I'm getting towards the end now. It pretty much all works as it should, though the the PID could still use some tuning.

One last thing I didn't mention. Temperature on the unit can also be controlled by 2 solenoid valves rather than the pneumatic valves. I don't see a reason why you'd want to do this, but that's the way it is setup. One valve will shut off hot water when energized and the other for will shut off cold. If i wanted to make a simple on-off control for this, is there any reason why the logic can't be pretty much the same as for the level control? Use 2 GEQ's for the limits, and when one valve is closed the other is open and vise versa? Is there a better way? I plan on trying it tomorrow if I can, but have been very busy these last 2 weeks.