help on pid instruction

i am trying to set up a pid instruction, what i want is to do is run a pump via scp instruction until i have got the pump upto pressure and the press a button on a hmi which will control the pump pressure in conjunction with a transducer?
i have started writing a program but i an stuck, can i place a button before a pid(turn it on/off)? and on a ml1200 what info do i put in the pid file?

thanks stu

Stu,
I am no PID guru like some others on here and actually I am less than a novice but I think it is best that you do not put conditions in front of the PID and on the ML1200 you will need to add a PID data file.
If you want to manually control it until some set of conditions are met then I would put your conditions to switch between manual and auto. The PID has a manual/auto bit.

To add your PID data table right click the data files ->New then click on the drop down list for data table type and select PID. PID is located at the bottom of the list.


Hope this helps get you started.

Greetings stu ...

in addition to the advice from my distinguished colleague Bob O, you should also consider that we can give you much better (and more detailed) help if you’ll post the .RSS file instead of just a screen shot ... that way we can tell a lot more about the hardware you’re using – and about how you have it configured ...

good luck with your project ...

hi i have not tried the transducer out yet, this project is my first bit of programing?please be gental thanks stu

As Bob O stated, you'll need a PD file. Do not manipulate the block directly, keep it always enabled. There's an auto/manual bit, set when in manual. In manual you can vary the output value and it starts from there when set to auto. If you disable/enable the block the output returns to zero and starts from there, can be quite a bump.

Are you going to use pressure or rpm as the process value? It's not clear from the listing.

Bob O is correct, it's best to put the PID function in manual.
Start by simulating the pressure input to see how the PID acts in Automatic.
A good starting point for PID settings would be Gain = 1, Integral = 0, Derivative = 0
Set your simulated pressure to half scale.
In manual set your output to 50%
Put the PID in Automatic, the output shouldn't change.
Increase the simulated pressure 10%
The Output should go down 10%, if it goes up you need to change the action from direct to reverse, sometimes this is done by entering a negative gain.
Once you get the loop working right you can try it with the transducer and pump.
Increase the output in manual until you get about 50% pressure then put it in Auto, the pressure should stay the same.
Increase the setpoint 10%, the pressure shouldn't go up more than 10%. If it does or starts to cycle up and down you need to reduce the gain, go a bit beyond where it stops cycling.
Now you can add a little reset say 1 repeat per minute (1 minute per repeat).
Once you have the settings right you should be able to raise or lower the setpoint in Auto and the controller will bring it to the setpoint without too much overshoot in a reasonable time.
Don't be tempted to ad any Derivative.
Hope this helps
Regards
Roy

ydtech said:

As Bob O stated, you'll need a PD file. Do not manipulate the block directly, keep it always enabled. There's an auto/manual bit, set when in manual. In manual you can vary the output value and it starts from there when set to auto. If you disable/enable the block the output returns to zero and starts from there, can be quite a bump.

Are you going to use pressure or rpm as the process value? It's not clear from the listing.

Click to expand...

hi thanks for that i have got hte data file now,i have just put a no contact(auto/man button) to energize pd10:0/AM which i think is the right contact? on the hmi i would like to put in a pressure (set point) how can i do that? i am going to use pressure.
thank you for you time.stu