maintpro
Member
I am having problems with the PID operations of my SIMATIC 545 PLC. We use the controller in a wax melting operation. The wax kettles are heated by steam and the PID is adjusting the valve position. The valve position range is -25% to 100%.
The problem is that when the PV is the same or greater than the SP, the the valves are occasionally still open 50% or sometimes greater (I say occasionally because it is not every time). This leads to overheating of the kettles and burning of the wax.
If we turn the steam off (this takes the loop out of auto) and then back on again, the output will correct itself. We have had this system in place for a number of years now and according to the operators, it has never worked properly to begin with.
My loop perameters are as follows:
POS/VEL PID ALGORITHM: POS
LOOP VFLAG ADDRESS: C702
SAMPLE RATE: 2.00 SEC
PROCESS VARIABLE ADDRESS: WX177
PV RANGE LOW: 0
HIGH: 300
PV IS BIPOLAR: NO
SQUARE ROOT OF PV: NO
20% OFFSET ON PV: YES
RAMP/SOAK PROGRAMMED: NO
RAMP/SOAK FOR SP: NO
ALARM DEADBAND: 0
MONITOR LOW-LOW/HI-HI: NO
MONITOR LOW/HI: NO
PV ALARMS LOW-LOW: 0
LOW: 0
HIGH: 100
HIGH-HIGH: 100
REMOTE SETPOINT: NONE
CLAMP SP LIMITS LOW: O
HIGH: 300
LOOP GAIN: 50
RESET: 35
RATE: 0
FREEZE BIAS: NO
DERIVATIVE GAIN LIMITING: NO
LIMITING COEFFICIENT: 10
SPECIAL CALCULATION ON: NONE
SPECIAL FUNCTION: NONE
LOCK SETPOINT: NO
LOCK AUTO/MANUAL: NO
LOCK CASCADE: NO
ERROR OPERATION: NONE
REVERSE ACTING: NO
MONIOR DEVIATION: NO
DEVIATION ALARM YELLOW: 100
ORANGE: 100
MONITOR RATE OF CHANGE: NO
RATE OF CHANGE ALARM: 0
MONITOR BROKEN TRANSMITTER: NO
This is the first time that I have had to deal with a PID system and am uncertain if these perameters, especially the gain, are correct.
I am also wondering if the problems are due to fluctuations in the process variable and if I should freeze this value for loop use by moving it into a V-register.
I have monitored the program and found that temperature values received by the plc are correct.
Any help you can provide would be greatly apprecieated.
The problem is that when the PV is the same or greater than the SP, the the valves are occasionally still open 50% or sometimes greater (I say occasionally because it is not every time). This leads to overheating of the kettles and burning of the wax.
If we turn the steam off (this takes the loop out of auto) and then back on again, the output will correct itself. We have had this system in place for a number of years now and according to the operators, it has never worked properly to begin with.
My loop perameters are as follows:
POS/VEL PID ALGORITHM: POS
LOOP VFLAG ADDRESS: C702
SAMPLE RATE: 2.00 SEC
PROCESS VARIABLE ADDRESS: WX177
PV RANGE LOW: 0
HIGH: 300
PV IS BIPOLAR: NO
SQUARE ROOT OF PV: NO
20% OFFSET ON PV: YES
RAMP/SOAK PROGRAMMED: NO
RAMP/SOAK FOR SP: NO
ALARM DEADBAND: 0
MONITOR LOW-LOW/HI-HI: NO
MONITOR LOW/HI: NO
PV ALARMS LOW-LOW: 0
LOW: 0
HIGH: 100
HIGH-HIGH: 100
REMOTE SETPOINT: NONE
CLAMP SP LIMITS LOW: O
HIGH: 300
LOOP GAIN: 50
RESET: 35
RATE: 0
FREEZE BIAS: NO
DERIVATIVE GAIN LIMITING: NO
LIMITING COEFFICIENT: 10
SPECIAL CALCULATION ON: NONE
SPECIAL FUNCTION: NONE
LOCK SETPOINT: NO
LOCK AUTO/MANUAL: NO
LOCK CASCADE: NO
ERROR OPERATION: NONE
REVERSE ACTING: NO
MONIOR DEVIATION: NO
DEVIATION ALARM YELLOW: 100
ORANGE: 100
MONITOR RATE OF CHANGE: NO
RATE OF CHANGE ALARM: 0
MONITOR BROKEN TRANSMITTER: NO
This is the first time that I have had to deal with a PID system and am uncertain if these perameters, especially the gain, are correct.
I am also wondering if the problems are due to fluctuations in the process variable and if I should freeze this value for loop use by moving it into a V-register.
I have monitored the program and found that temperature values received by the plc are correct.
Any help you can provide would be greatly apprecieated.