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Hi List,
Could you help me on this please?
We have a temperature control (An outlet Temp PID cascading to a Fuel Gas Flow PID) in the Oil furnace/preheater, most of the time the control work OK but when it rained in the field the temperature of the incoming oil crude would lower significantly. The heater temperature control, would "wind up" on integral and cause the burners to go to max fire, 100% gas flow for extended periods. Maintaining max fire for extended periods would result in High High Bridge Wall Temperatures and a subsequent shutdown of the furnace.
The Process Eng. wants to use a limiter (55%) to limit the output of the gas flow controller to 55% and still maintain reasonable normal operation while avoiding the trip when the field experienced rain.
I don not like this solution because when the weather is sunny we would get a offset problem (it cannot reach it's setpoint).
I am considering to use a low controller output selector {pid.out = LS(master.pid.out; bridge.pid.out)} with a additional temp. controller and transmitter (bridge wall temp.) instead of the limiter. What do you think about this idea?.
Thanx,
Félix Blanco
Could you help me on this please?
We have a temperature control (An outlet Temp PID cascading to a Fuel Gas Flow PID) in the Oil furnace/preheater, most of the time the control work OK but when it rained in the field the temperature of the incoming oil crude would lower significantly. The heater temperature control, would "wind up" on integral and cause the burners to go to max fire, 100% gas flow for extended periods. Maintaining max fire for extended periods would result in High High Bridge Wall Temperatures and a subsequent shutdown of the furnace.
The Process Eng. wants to use a limiter (55%) to limit the output of the gas flow controller to 55% and still maintain reasonable normal operation while avoiding the trip when the field experienced rain.
I don not like this solution because when the weather is sunny we would get a offset problem (it cannot reach it's setpoint).
I am considering to use a low controller output selector {pid.out = LS(master.pid.out; bridge.pid.out)} with a additional temp. controller and transmitter (bridge wall temp.) instead of the limiter. What do you think about this idea?.
Thanx,
Félix Blanco