Hochiki Kabushiki Kaisha

Yasuo Torikoshi

Hiromitsu Ishii

A thermal analog fire detector which is excellent in measurement precision and resolution in both the high and low temperature ranges and which has a wide range of measuring temperatures. A constant voltage E from a constant voltage circuit is supplied to a CPU, an A/D converter and a constant current circuit. The constant current circuit is connected in series to a thermistor. The constant current circuit is constructed to supply a constant current, the value of which being variable in a plurality of stages, to the thermistor controlled by the CPU. The CPU switches the constant current of the constant current circuit according to the measured temperature data. A voltage V across the thermistor is converted into digital data by the A/D converter, and then the converted data is supplied to the CPU.

Thermal analog fire detector

A pair of temperature detection devices having different heat time constants and an active device having a predetermined bias are connected in series. The bias is set so as to cause the active device to operate in a saturated region if the temperature is higher than a dangerous level, and to operate in a triode region if the temperature is lower than the dangerous level. The temperature detection devices are chosen so as to cause the voltage generated at the junction of the temperature detection devices to be higher than a predetermined reference voltage if the temperature has been raised to the dangerous level when the temperature is raised slowly, or if the temperature is raised rapidly, even if the temperature is lower than the dangerous level. A constant temperature function and a differential function are generated to detect that a fire has taken place. In another embodiment, one of the temperature detection devices (in series with an active device) is arranged in parallel with the other temperature detection device (in series with a resistor). The relative voltages of the two temperature detection devices are monitored to detect a 'too high' or 'too rapidly increasing' temperature. The resultant compensation type heat sensor has a reduced number of elements, the cost of which can be reduced and which possess both the constant temperature function and the differential function.

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Kawasaki, Japan

Yasuo Torikoshi