PID help....

Everyone has been a big help on this site. I am new to PID Commands and have a problem at work in that I have been asked to update an old auger system to touchscreen with recipes. These recipes run 3 augers by suppling the correct RPMs setpoints. I have a program that comes up with RPM's from a HSCE module as feedback for my PID and was told some stuff on how to set up the PID to keep the RPM's. I got lost in the setup screen and need some help. the highest RPMs the motor will be allowed to go is 2400 RPMs. I have not yet tackled the touchscreen but assume this will be values sent to the interger file I set up for the touchscreen. Using the program I am including, How would I make this PID go to a RPM setpoint made by the touchscreen and keep the RPM at that setpoint. An example would be like if auger #1 has be told to go to 1900 RPMs by a recipe and keep that setpoint. I am using DC Motors controlled by a analog card. There is a encoder that sends pulses to a HSCE module that I use to get RPM feedback. I am using a SLC 5/03 processor. Please send me some examples especially on setting up the PID and the setup screen. I also am not sure if the SCP command is set right. I am using the analog card to send voltage to the wiper input to control the DC Drive. The Drive is very simple and only has Amature outputs.

Just a quick glance and I see you need quite a bit of help.

Timing for a PID is critical, so I recommend setting it up into it's own subroutine, which is triggered at a periodic rate of time using the controller's STI function. Search for STI in the help file and read up.

You must scale the PID setpoint and PV into the PID. So if you have rpm range of 0 - 2400, that needs to be scaled to the PID as 0 - 16383. The output will have to be scaled back to rpm/%...

The PID function has "Output Max" CV that can be setup in the PID. This is in %, so you can put in 85%, to cap your output. Depending on the RPM range your cap % will change and you'll need to calculate that value. If you have a range of 0 - 3000 RPM, and you need to cap it at 2400...calculate the equivalent of 2400 RPM given 0 - 100% range.

Do you understand the E = SP - PV and E = PV - SP differences? If you don't, you'll have a heck of a time. Read up on direct/reverse actting controllers.

Are you familiar with tuning?

Read the PID instruction help many many times until you understand the PID stucture and all the components to it.

PID's are not simple to understand, I highly recommending www.controlguru.com, specficly the entire heat exchanger example.

I'm just giving you some homework subjects, read up and come back with more questions once you've some background of the above.