Load limiter for multiple electric heater loads - uses triacs to chop half-cycles from each heater circuit in succession

摘要

If an electric heating installation consists of a number of separate resistance loads, it may be required to limit the total power drawn from the supply. This can be done by an overload relay cutting off the whole load either by chopping the voltage with thyristors or triacs or by chopping entire half-cycles electronically. Each of these has disadvantages. Half-cycles can be chopped from the supply to successive heaters in turn. A current transformer or shunt supplies a stepless rectifier amplifier which in turn supplies an exponential amplifier. A ring counter counts half-cycles and actuates in sequence switches controlling the supply to the individual heaters. A switch energises a step size modulator which in turn controls a triac via its control circuit.