| 摘要 |
A timer controlled smoke detecting thermostat has been designed. A control circuit provides for two set point temperatures and time settings for controlling the periods during which one or the other of the set-point temperatures is to be maintained. Means for detecting smoke and sounding an alarm has been built into the thermostat as well as means for inhibiting on states of a controlled heating or cooling unit to prevent air currents in the presence of smoke to reduce the speed at which fire might spread. The thermostat operates on a small leakage current flow through the heating or cooling unit. In addition to supplying power to the thermostat, this leakage current charges a battery so that when full power is applied to the heating or cooling unit and there is no leakage current, power is supplied to the thermostat by the battery. The selection of the temperature to be maintained is made time dependent through the use of an integrated-circuit clock. Temperature control is achieved by two voltage dividers each comprised of a thermistor and a variable resistor. The thermistors are detectors of ambient temperature and the variable resistors are inputs for temperature set-points. Either voltage divider can supply sufficient voltage to turn on a silicon controlled rectifier which causes full power to be applied to the heating or cooling unit. However, the integrated-circuit clock causes the application of voltage to only one of the voltage dividers at a time and, thereby, selects the set-point temperature to be maintained. Smoke is detected by causing light to be scattered onto the base detector of a photodarlington transistor located in a smoke chamber. Resulting fluctuating signals from the photodarlington are used to turn on a second silicon controlled rectifier which disables the ability of the temperature control portion of the thermostat to apply full power to the heating or cooling unit.
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