Electricity: power supply or regulation systems – Remote sensing
Patent
1974-11-11
1976-06-01
Pellinen, A. D.
Electricity: power supply or regulation systems
Remote sensing
323 25, 323 68, 323 69, G05D 2324
Patent
active
039612376
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. The second thermostatic device is set at a higher set temperature point, such as 78.degree.F. minimum, with an adjustment mechanism permitting resetting of this temperature to a higher value, e.g., to 85.degree.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.
REFERENCES:
patent: 2917288 (1959-12-01), Sims et al.
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patent: 3166246 (1965-01-01), Fielden
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patent: 3305176 (1967-02-01), Brace
patent: 3597676 (1971-08-01), Moore
davis, "Temperature Control System Based on Thermistor Bridge," Control & Instrumentation, Apr. 1971, vol. 3, No. 4, pp. 35, 37.
Pellinen A. D.
Robertshaw Controls Company
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