Still trying to get my head around this PID PV input scaling thing.
What I am trying to do is to add a 2nd (user selectable PV input to a single PID control with analog inputs with two different input transmitter ranges.
The existing input device range is 0 to 200 RPM.
In the PID config block, original programmer used "O - 8000" for input scaling for this transmitter. How did he arrive at this value?
New transmitter being added is ranged to 0 to 150RPM and connected to the same analog input card. Both inputs are 4-20 ma signals. Now if I allow this 2nd input to go in to existing PID as a selectable PV input, wouldn't my RPM value be totally off because of the current Input scaling inside the PID?
How would I add this transmitter so both would utilize the same PID control block? Do I have to scale the 2nd transmitter via logic before feeding it in to the PID? I dont see any other way to do it. Any calculation help, formulas etc to resolve this would be greatly appreciated.
I would really like to know where the scaled input value of 8000 came from or how it should be calculated. I could not find anything in the data sheets and PLC-% instruction ref. confused me even more.
Thanks.
What I am trying to do is to add a 2nd (user selectable PV input to a single PID control with analog inputs with two different input transmitter ranges.
The existing input device range is 0 to 200 RPM.
In the PID config block, original programmer used "O - 8000" for input scaling for this transmitter. How did he arrive at this value?
New transmitter being added is ranged to 0 to 150RPM and connected to the same analog input card. Both inputs are 4-20 ma signals. Now if I allow this 2nd input to go in to existing PID as a selectable PV input, wouldn't my RPM value be totally off because of the current Input scaling inside the PID?
How would I add this transmitter so both would utilize the same PID control block? Do I have to scale the 2nd transmitter via logic before feeding it in to the PID? I dont see any other way to do it. Any calculation help, formulas etc to resolve this would be greatly appreciated.
I would really like to know where the scaled input value of 8000 came from or how it should be calculated. I could not find anything in the data sheets and PLC-% instruction ref. confused me even more.
Thanks.