PLC PID Auto Tuning Problem

monet

Member
Join Date
Feb 2009
Location
Wien
Posts
2
hiii

i'm using Siemens S7-200 (PID Control Panel) to control speed of DC motor.
I have sensor which detects speed of motor [0V ; 2.84V] and that's Analog Input A (PV-Process Value). I use potentiometer to set value [5V ; 10V] and that's Analog Input B (SP-Setpoint). Analog Output is connected to the motor. I configure PID loop through PID wizard, but when i run PID Control Panel it seems like there is a problem with SP (Setpoint) because it doesn't change even if I change value on potentiometer. Is there something with SP that i'm forgeting, or the problem is somewhere else? Can someone who has done this before explaine me how to do it right?

Anyone?:confused:

thanks
 
First of all, tell us how your motor is connected to the PLC, and how big your motor is ?? Even if you PID is not working your SP must change when you move your potentiometer, use a voltmeter and measure analog input from your potentiometer. A sketch would be helpful. Are you using a DC drive ??
 
hi widelto
DC motor is small, and analog output of PLC is connected over OP amplifier with it. i'm sure there is no problem with current. I've also checked potentiometar and measured analog input of PLC with voltmetar and it shows correct value. I've checked hardware various time and it works good. So i think there's some kind of problem in the PLC with SP, because in PID wizard SP is converted into ''REAL'' and saved on VD0 location. Either some conversion should be done or there's scaling problem??
 
Double check potentiometer correctly hooked up. Double check that at input you get voltage variation. Double check that voltage variation on meter correlates correctly to PLC analog value.

Dan Bentler
 
Analog I/P Module

Check your Analog input module Dip Switch setting and Connections?
Ensure the addressing is Correct(for Second Channel of Analog input it will be AIW2).
Just got to status and view the AIW2 input raw value.
Tell us what type of Analog Module you used for further analysis.


SathyaNarayanan
 
If you are using a 4-20 ma input module with a speed pot you will get a pretty similar result to what you have . Make sure your input card is a voltage input and not current like sathya max said.
 

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