Pid Normalizing Loop Inputs/Outputs

Hi Everyone

Siemens S7-200 Pid: Software Version v4 sp3

I have a need for 8 pid loops which is okay.
Where my problem is do i have to Convert and Normalizing Loop inputs
do i have nomalize each input ie the sepoint,Pv and Output if i do how the heck do i do it, siemens tech help said i would have to do some maths fine but how?

Many Thanks from Sunny Scotland

All they really mean is that the setpoint value and the feedback value need to be in the same units and need to 'fit' in the range of the PID input. In addition the output will probably need to be scaled so it is in units the output device can use.


I'm not real familiar with the S7-200 so I don't know if they have any built-in scaling functions. But anything you can do with a scale instruction you can do with the basic math functions.

Again, the big thing to keep in mind is that the setpoint and the process variable are in the same units, be that bits or volts or degrees. When the process variable physical value matches the setpoint the numbers for each in the PLC should be the same.

Keith

The S7-200 has a PID Wizard under tools>instruction wizard. The wizard creates a subroutine with the PV, SP, Manual output etc. All you need to do is call the subroutine on the main program. You don't need to normalize the PV to 0.0 to 1.0. You can connect the PV, say Analog input directly to the subroutine. You will specify in the wizard the scaling ranges..

Hope this helps.. Let me know if you have any questions

Correct. The normalization actually applies to the output I think. I have used this in temperature control and it works nicely. However, I specified a pulse width modulated output(versus analog output) in the wizard. This is because I was using a solid state switch to modulate power to the heater. It controlled temperature to better than +/- 1 degree F which was good enough for my application.

Cryogen said:

The S7-200 has a PID Wizard under tools>instruction wizard. The wizard creates a subroutine with the PV, SP, Manual output etc. All you need to do is call the subroutine on the main program. You don't need to normalize the PV to 0.0 to 1.0. You can connect the PV, say Analog input directly to the subroutine. You will specify in the wizard the scaling ranges..

Hope this helps.. Let me know if you have any questions

Click to expand...

thx guys that;s helps a lot, but one more question to i normalize the setpoint.

Again many thanks

No, do not normalize either setpoint or process variable.

voyage said:

thx guys that;s helps a lot, but one more question to i normalize the setpoint.

Again many thanks

Click to expand...

Thx PPL working like a dream now

Many Thanks Voyage