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 ° f . maximum with an adjustment mechanism permitting adjustability to a lower set point temperature , e . g ., to as low as 55 ° f . the second thermostatic device is set at a higher set temperature point , such as 78 ° f . minimum , with an adjustment mechanism permitting resetting of this temperature to a higher value , e . g ., to 85 ° f . the thermostat is used in combination with a signal conditioning circuit which comprises an operational amplifier in a comparator circuit having a reference leg and the thermostat leg supplied with a special regulated direct current power supply . this circuit includes a protective solid state switch to prevent accidental destruction of the circuit components in the event that the circuit is inadvertently grounded during installation or repair .