Abstract: There is disclosed a motor control circuit that is particularly useful for the control of a damper motor in a heating and ventilating system. The control circuit comprises a bridge circuit having a pair of operational amplifiers with cross connected input terminals. An input signal is provided by input signal circuit means to one of the cross-connecting conductors and a reference signal is provided to the other of the conductors by a reference signal circuit means. The operational amplifiers are provided with feedback circuit means between their output and noninverting terminals to drive the amplifiers into an unstable condition where they function as on and off switches. Dead band means in the form of a load dropping resistor is provided between the input signal circuit and the noninverting terminal of one of the amplifiers.

Abstract: A thermostatic device for generation of a plurality of direct current analog signals responsive to temperature deviation of a control zone from a plurality of set temperature points. The device has a plurality of direct current voltage signal generators, each of which includes a thermistor with a negative temperature coefficient in circuit with a variable resistor and an adjustment mechanism associated therewith whereby the value of the resistor can be fixedly adjusted to provide a limited degree of adjustability of the set temperature points. The adjustment mechanism includes fixed stops whereby the lowermost set temperature point can not be raised and the uppermost set temperature point can not be lowered. In a typical embodiment, the thermostat comprises two thermostatic devices, one set at a lower set temperature point of about 68.degree.F. maximum with an adjustment mechanism permitting adjustability to a lower set point temperature, e.g., to as low as 55.degree.F.

Abstract: There is disclosed an air conditioning control system for a building which has zone temperature sensing means for generating a plurality of DC analog signals proportional to the deviation of the air temperature in a controlled zone from first and second set point temperatures. The signal generated by the deviation of the controlled zone air temperature below the lowermost set point temperature is applied to the controller of the air heating facility of the air condition system while the signal generated by deviation of the controlled zone air temperature above the highest set point temperature is applied to the control means for the air cooling facility of the air conditioning system.