Parallel Positioning Control Systems Parallel Positioning Control (PPC) systems function very much like a Fixed Position Parallel system except that the fuel and air end devices are separated and driven by their individual positioners. Modern PPC systems incorporate an end-device positioning signal, which ensures the fuel and air positioners have moved to their pre-specified positions for a specific firing rate. This signal, while not actually proving final end device position and true fuel/air ratio flow, is a marked improvement over FPC systems.
The new systems are gaining wide acceptance with many users who have traditionally used FPC systems and are seeking an economic means to improve overall combustion efficiency. The modern PPC system is suitable for boilers ranging from 100 through 900 Boiler horsepower with relatively stable loads.
Modern electronic positioning PPC systems can hold excess oxygen levels to within 4-6% on many applications. It should be noted however that the PPC control strategy should be used with caution in applications with extremely fast load swings, as controllers and positioners which might be set too tightly may not properly respond and still maintain a safe fuel/air ratio on large and fast upsets.