I'm using an Automation Direct SL4848-CR to control stuffing pressure to a centrifugal milk separator. The problem I'm trying to overcome may be applicable to other process controllers.
Basically, the process controller works fine, but I want to temporarily halt PID operation when the separator discharges (de-sludges). For now, I have the process controller communicating with a PLC over Modbus. When the PLC detects separator discharge, it changes the mode of operation of the process controller from PID to Manual and saves the "last good" output that was read from the process controller, which it sends back to the process controller while it's in manual mode. This part works great.
My issue is that when I switch the process controller back to PID mode after discharge, the output changes back zero. Since it's a "slow" loop, it sometimes takes several minutes for the stuffing pressure to stabilize. Is there a way to pre-load the output variable with the "last good" output before the discharge while in PID mode? If not, is there a way to start the output at a value other than zero?
Basically, the process controller works fine, but I want to temporarily halt PID operation when the separator discharges (de-sludges). For now, I have the process controller communicating with a PLC over Modbus. When the PLC detects separator discharge, it changes the mode of operation of the process controller from PID to Manual and saves the "last good" output that was read from the process controller, which it sends back to the process controller while it's in manual mode. This part works great.
My issue is that when I switch the process controller back to PID mode after discharge, the output changes back zero. Since it's a "slow" loop, it sometimes takes several minutes for the stuffing pressure to stabilize. Is there a way to pre-load the output variable with the "last good" output before the discharge while in PID mode? If not, is there a way to start the output at a value other than zero?