Why does the controller overshoot the set point?
A. Pump is too large: Calculate the flow rate required. The metering pump should be set for no more than 1.5 times the expected depletion rate of the chemical. Either adjust the flow rate of the pump down to this level, or replace the pump with one that better matches the required flow rate. B. Pump is siphoning: Install anti-siphon valve on metering pump, or on metering pump discharge line. Avoid “down hill” tubing runs. A metering pump injecting into open atmosphere can pump more than its rated capacity if an injection check valve is not installed. C. Poor mixing/large lag time: Improve mixing, or move the location of the sensor and/or replenishment so that chemical additions reach the sensor faster. If using a flow-through sensor, make sure that the flow rate through the sampling system is sufficient (less than 1 minute to detect additions). If the lag time cant be improved, then in pH/ORP applications, a proportional controller should be used. For other applications, it may be poss
