PID Loop Control / RSLogix

Ron,

I do not feel you let me down in any way. All you did was explain that you do not have what I need -- BUT -- you sent me to someone who does have it.
Your explanation on the NT 4 helped fill in some of the blanks in the Rockwell manual. The inputs and outputs on NT 4 threw me for a loop for a while. I guess it is like the terms supply and return in chill water or other circ systems. Gotta know who is the source and who is the user. Thank you for steer to the manual I had the 1995 manual but the web page had the 2004 -- kinda handy to have updated info.


Randy thanks for steer to the Petruzella text. Will check to see if local library has copy or can obtain. I like to test drive text books before purchase.

Many thanks for the help


Dan Bentler


Your
 
I know this is already posted. I want to get a copy to my printer at work.

Kindly ignore

Dan Bentler


Ron Beaufort said:
Greetings wwcoop,

with the PLC-5, there are two basic ways to set up the PID ...

(1) the old way (and there are still tons of these in use today) uses a 23-word integer-style control block (example: N7:100 through and including N7:122) ... with this type of PID, you will not be able to enter “floating point” numbers for any of the settings ... but that’s ok ...

(2) the new PD-type control block (only available with “enhanced” PLC-5 models) will require you to create a new data file (example: PD9:0) to contain the PID control structure ... this method allows “floating point” entries and more flexible settings ... we’ll eventually learn about this method too if you want to go that far ...

if you’re trying to make your experience as portable as possible, then I recommend that you start with the older integer-type control and we’ll go from there ...

I recommend that you “simulate” a 1771-IFE analog input module with a 4-20mA input ... you don’t need to actually program in the “simulated” module - but you must have a realistic address for the Process Variable (PV) ... I suggest N7:54 ...

you need to specify the minimum (4mA) temperature reading for your temperature transmitter ... for right now I’ll assume (gosh I hate that word) that you’ll be using 0 degrees F. ... this will correspond to a data reading of 0 at the PV ...

you also need to specify the maximum (20mA) temperature reading for your temperature transmitter ... for right now I’ll assume (I still hate that word) that you’ll be using 250 degrees F. ... this will correspond to a data reading of 4095 at the PV ......

I recommend that you “simulate” a 1771-OFE2 analog output module with a 4-20mA output ... you don’t need to actually program in the “simulated” module - but you must have a realistic address for the Control Output (CV) ... I suggest N7:75 ...

this setup means that a CV signal of 0 at N7:75 will generate an output of 4mA to the control valve in the field ... also ... a CV signal of 4095 at N7:75 will generate an output of 20mA to the control valve in the field ... for now we’ll assume (man that word is killing me) that 4mA will close the steam valve completely ... and that 20mA will open the valve completely ...

[attachment]

the yellow highlighted settings temporarily put the PID into the “Set Output Mode” for testing the input and output signals ... this is basically one type of “manual” control mode ... with the settings I’ve given, the CV at N7:75 should go to a steady value of 1024 (4095 times 25% equals 1024) ... then you should be able to increase and decrease the CV by changing the “Set Output Value” ... if your “simulator” is working correctly, the PV should start to increase and decrease as you manually open and close the valve ... specifically, the value at N7:54 should increase and decrease between 0 and 4095 ... and the “Scaled PV Value” on the PID setup screen should increase and decrease between 0 and 250 degrees ...

suggested plan of attack:

(1) let us know when you’ve got this much working ...
(2) post your current .RSP program file ...
(3) ask specific questions about specific entries that have you puzzled ... be sure to tell us what you’ve already tried ... and what results you expected ... and what results you saw ... and why those results have you puzzled ...

you can find the official description of the PID instruction as used in the PLC-5 in Chapter 14 of:

The PLC-5 Instruction Set Reference Manual

so ... are we having fun yet? ...

in your first post you said:

now in the picture above you have almost all of the settings involved for one very popular method of setting up a PID ... so which of these settings are giving you the most trouble? ... we’re ready to help ... just tell us where it hurts ...
 
Hello Ron,

is there any way I can sign up a week long training? Also can you post a PID control loop with PD type control block?

-Thank You
-Nayeem
 

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