jbjbj
Member
This is the first time I am trying to use a RSLogix 5000 PID and my lack of understanding this is version of a PID instruction is driving me crazy.
I am trying to control temperature ( avg. of 2 thermocouples ) using a proportional steam valve ( primary heat with the secondary (heating) fluid being 30% glycol.
My main problem is getting the PID configured/scaled correctly.
I am at the end of development and thought I would simulate the PIDs before shipping, to get a feel for how they respond.
However, I can’t get it to do anything except slam on and off.
This very well could be due to my P and I setting, since I can’t figure what the values are relative to ( max/min PV scaling?, eng units?, DINT? ) but my lack of understanding ( and ability to decipher the available help ) goes deeper than that with this PID instruction.
So…. Mainly working on PID_TEMP in “Heating”
I scale, in the PLC, the HMI temp set point to –346 to 2192 = 0 to 16383 ( type j thermocouple limits) and move that to PID_TEMP.SP, fine and well.
My process variable (DRY_SHELF_TEMP_AVG_PID) is from temp inputs also scaled (in PLC) 0-16383.
My Control variable is assigned to an analog out (Local:7:O.Ch1Data ) configured to 4-20 Ma.
I had an arbitrary P of 300 and I of 100.
I set up a couple to test bits to toggle on and off as required to enable the PID and allow me to write new temperature feed back. First attempt had no PID internal scaling set.
This would respond to a difference of set point vs. feedback by slamming the output (CV) on or off. At least it goes in the right direction.
I then noticed that I had no scaling set, so I set max/min PV 16383 to 0. Same results. eng units? Hmm. , I tried both none and –346 to 2192, this was now giving me odd process variable “display” on the PID.
I guess it comes down to I can’t fathom the relationships between these settings to The PID function and the relationship (scale ) of the P and I settings.
( oh yeah, on line I see a tieback value 4095-0 and can’t do anything about it, (regardless of PID enabled checkbox resets)
If I can get these working here, I can “tune” via brute force if required in the field.
Hopefully someone here has some experience with the 5000 PID (dependent version) and might be able to point me in the right direction.
I’ve attached the preliminary program (RS5000 v15) and for reference a HMI screen shot of the main process.
Thanks!!!
*edit* I can't post an .ACD type file and it's also to big 327k
I am trying to control temperature ( avg. of 2 thermocouples ) using a proportional steam valve ( primary heat with the secondary (heating) fluid being 30% glycol.
My main problem is getting the PID configured/scaled correctly.
I am at the end of development and thought I would simulate the PIDs before shipping, to get a feel for how they respond.
However, I can’t get it to do anything except slam on and off.
This very well could be due to my P and I setting, since I can’t figure what the values are relative to ( max/min PV scaling?, eng units?, DINT? ) but my lack of understanding ( and ability to decipher the available help ) goes deeper than that with this PID instruction.
So…. Mainly working on PID_TEMP in “Heating”
I scale, in the PLC, the HMI temp set point to –346 to 2192 = 0 to 16383 ( type j thermocouple limits) and move that to PID_TEMP.SP, fine and well.
My process variable (DRY_SHELF_TEMP_AVG_PID) is from temp inputs also scaled (in PLC) 0-16383.
My Control variable is assigned to an analog out (Local:7:O.Ch1Data ) configured to 4-20 Ma.
I had an arbitrary P of 300 and I of 100.
I set up a couple to test bits to toggle on and off as required to enable the PID and allow me to write new temperature feed back. First attempt had no PID internal scaling set.
This would respond to a difference of set point vs. feedback by slamming the output (CV) on or off. At least it goes in the right direction.
I then noticed that I had no scaling set, so I set max/min PV 16383 to 0. Same results. eng units? Hmm. , I tried both none and –346 to 2192, this was now giving me odd process variable “display” on the PID.
I guess it comes down to I can’t fathom the relationships between these settings to The PID function and the relationship (scale ) of the P and I settings.
( oh yeah, on line I see a tieback value 4095-0 and can’t do anything about it, (regardless of PID enabled checkbox resets)
If I can get these working here, I can “tune” via brute force if required in the field.
Hopefully someone here has some experience with the 5000 PID (dependent version) and might be able to point me in the right direction.
I’ve attached the preliminary program (RS5000 v15) and for reference a HMI screen shot of the main process.
Thanks!!!
*edit* I can't post an .ACD type file and it's also to big 327k