FX2N PID

[swimmy67 9]

Does anyone have experience with the PID function in a FX2N plc. I am using GX Developer Ver 7.11. Attached is the program that I am using. I can not control the PID from the beginning. The only time that I enable the PID function is when the process temp is within 5 deg of the setpoint temp. When within this range, I load a max and min value into the output min/max variable so the output will function say between 15% to 50%. At any other time the output is 100% if more than 5 deg below setpoint, or 0% if more than 5 deg above setpoint. I am trying to control a heat exchanger. I am using a FX2N-4DA output card with the analog signal set to 4-20ma. A Honeywell Modutrol actuator to open or close the damper. Any help in this manner would be greatly appreciated. Thanks, Kari Swimelar Electrical Engineer KJC Electric Inc.

[swimmy67 9]

Hello all, It seems that the file did not get attached. Here is ths program. Thanks, Kari FX2N_PID.zip

[waynes 8]

Hi swimmy67, usually when using a pid in a heating application, you set the pid the reverse control: ie. increase output to increase pv; So, set d51 to h31. (Unless you are cooling) Your sampling time is 2s, why? Input filter is very high, try something like k10... I personally hate the kd (d55), set to k0. Same with td (d56). Also, ensure kp and ti have valid values. If they do not, the PID will not respond correctly. Why can you not enable the PID all the time (after startup conditions are ok). It should automatically open up the modutrol all the way? If the PID is tuned ok, then it will respond appropriately to the process. I have uploaded the programming manual for the FX?N. FX1S-FX1N-FX2N Prog Man (Complete Man) JY992D88101C.PDF Check under the downloads section, Mits| Manuals| Good luck.

[waynes 8]

Shortcut is http://forums.mrplc.com/index.php?act=Downl...&CODE=03&id=450

[swimmy67 9]

waynes, Thanks for the responce. Concerinig the sampeling rate, what would be a good time? Is 2sec too great of a sampeling time? Looking through the program, I am setting d51 to H33. during the run process. For autotune I am loading H30 into d51. I have read and reread the manual for the FX2N PLC. In section 10, there is a more detailed discription of the PID loop with example code. Still, when I try using the sample code, I can not get the PID to function correctly. The code that I posted is what the machine will run. I guess I need some more experience with the Mitsu PID function. This is my first time using the Mitsu FX2N PLC and the PID Function. I normally program with Allen Bradley SLC and ML PLC's. Thanks for your help in this matter. Kari

[waynes 8]

Hi swimmy67, Just remember to set d51 to h33 before running the pid loop. all parameters must be set before executing the instruction. Therefore, if you adjust the kp, ti, kp or td parameters, you need to pulse the instruction off for one scan and then continue again. Try running the PID without autotune; simulate the pv changes if need be. I have tried the autotune before, but without success. So, i usually tune it manually. You will need to finetune in anycase. Hop this helps

[mjrx 1]

Thats interesting. . . You mean you can't see any reflected gain changes until the PID loop is stopped and then restarted?

[waynes 8]

Yes, I have tried and tested in numerous ways. This is one flaw that I saw with this PID. There must be a reason for this. All I do is check to see if there is a P, I or D change and then pulse a bit that causes the PID to cease for 1 scan. The result is that the PID starts calculating again, first the P, then I, then D.

[rocket123 0]

Dear sirs!

 

can you let me know where is storing the MV data of PID - S3+?. i dont see anywhere in the parameter table in manual

 

many thanks

 

Edited 2 Nov 2016 by rocket123