| 摘要 |
PURPOSE:To enable the indication of a resistance value of an object to be measured, such as a coil or a heater, and to prevent the burning thereof due to overheat, by a method wherein a measured voltage from a voltage measuring/resistance value conversion indicator and a set threshold voltage from a reference voltage unit are compared with each other to be detected. CONSTITUTION:An AC voltage is impressed from an AC power source element 3 on an object 2 to be measured, such as a coil or a heater, and a heater, and a DC current from a DC power source unit 6 is superposed thereon. Then a DC drop voltage of the object 2 to be measured is measured by a voltage measuring/resistance value conversion indicator 8, and a resistance conversion value is thereby indicated. A reference voltage unit 9 sets a limit threshold value equivalent to a heating limit resistance value of the object 2 by impression of voltage. A voltage comparator 10 compares a measured voltage from the indicator 8 with a set voltage from the reference voltage unit 9 for detection, and a power source cut-off unit 11 is controlled by an output signal of the element 10. According to this method, the resistance value can be measured in the state that the AC voltage is impressed on the object 2 to be measured, while the power source cut-off element 11 can be controlled by the output signal from the voltage comparator 10 when the measured value reaches the set voltage, so as to interrupt the impression of voltage on the object 2 and thereby to protect the object 2 from overheat.
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