Thermostat using pulse width modulation control of circulation pump - uses wheatstone bridge temp. transducer feeding comparator supplied by sawtooth waveform to supply circulation pump

摘要

The temp. regulator for a central heating installation gives reduced temp. fluctuation owing to the control 'dead-zone' by using ramp generated pulse width modulation control of the circulation pump motor at the maximum repetitive starting frequency allowable for the motor. A temp. sensitive resistor is connected in a Wheatstone bridge with a temp. setting resistor which is connected via a contact on a timing clock. The bridge output supplies a comparator which is also supplied by a ramp generator. The operating frequency of the ramp generator is less than the maximum repetitive start frequency of the circulator pump motor. The duration of each operation of the motor is determined by the time for which the temp. error is greater than the ramp generator output.