ABSTRACT
This chapter describes the electronic instrument components that make up a typical multiloop system. The process is one found within the boiler room of most process plants— a feedwater control system for a boiler drum. Steam flow out of the drum is measured in terms of steam pressure, which is measured with a pressure transmitter. The operation of the pressure transmitter is similar to the operation of the differential pressure transmitter. The square root extractor is a nest-mounted card that accepts a signal input from the differential pressure transmitter and produces a 0 to 10 volt output signal proportional to the square root of the input. It is used primarily in conjunction with differential pressure transmitters to produce an output directly proportional to flow. The usual procedure for adjustment of a multiple-control loop is to isolate the loops and adjust them one at a time. The feedwater flow controller will normally have a wide proportional band and a fast integral.
