Routine plant power line fluctuations can upset the temperature of heated processes. For example, a 2% voltage change to the load equates to a 4% wattage change. Conventional controllers can only correct the upset through slow PID action or must employ expensive SCRs to compensate. The Series 2000 monitors line voltage continuously and instantly adjusts controller output to compensate for line fluctuations before temperature upsets can occur, even on mechanical contactor loads.