tgaljar
Member
Hi guys,
I have one question about PID loop. I am doing system that controls flow of water and it consists of flow meter (has output 4-20mA) and valve (has output which shows % of opening and three inputs OPEN, STOP and CLOSE).
So I have decided to use PID function to calculate desired percentage of valve opening. Input to PID is flow and I am scaling output to 0-100%.
Than I am subtracting PID output of current scaled output of valve and if result is negative valve goes into opening and if it is positive valve goes to closing. Valve is stopped when difference between PID output and current output are almost equal (+/-2%) and that means flow is around 25l/s.
My questions are:
Do I need to scale input value of flow as “scaled for PID”?
Can PID scale output to 0-100% or I need to use scale function?
Flow is 25l/s and valve needs 1min from open to close do I need to calculate PID output every PLC scan of once in second is enough?
AND IF THIS IS NOT GOOD IDEA DOES ANYONE KNOWS BETTER?
My problem is also that I don’t have PLC just a simulator (which doesn’t simulate PID) and I want to be sure that this will work in a real plant!
Thanks!
I have one question about PID loop. I am doing system that controls flow of water and it consists of flow meter (has output 4-20mA) and valve (has output which shows % of opening and three inputs OPEN, STOP and CLOSE).
So I have decided to use PID function to calculate desired percentage of valve opening. Input to PID is flow and I am scaling output to 0-100%.
Than I am subtracting PID output of current scaled output of valve and if result is negative valve goes into opening and if it is positive valve goes to closing. Valve is stopped when difference between PID output and current output are almost equal (+/-2%) and that means flow is around 25l/s.
My questions are:
Do I need to scale input value of flow as “scaled for PID”?
Can PID scale output to 0-100% or I need to use scale function?
Flow is 25l/s and valve needs 1min from open to close do I need to calculate PID output every PLC scan of once in second is enough?
AND IF THIS IS NOT GOOD IDEA DOES ANYONE KNOWS BETTER?
My problem is also that I don’t have PLC just a simulator (which doesn’t simulate PID) and I want to be sure that this will work in a real plant!
Thanks!