| 摘要 |
PURPOSE:To contrive the securing of the safety as well as the improvement of reliability by one thermistor, by a constitution wherein the output of the thermistor is decided by two operational amplifiers and alarming operation is effected by one operational amplifier through a control circuit consisting principally of a micro-computer while a relay is operated to intercept a power source circuit by the other operational amplifier through a transistor. CONSTITUTION:When a switch 16 is closed, a voltage is impressed on a DC power source 22 and a DC voltage is generated across section m-n. A control circuit 12' and a thermo circuit 37 are operated by the voltage to effect the detections of disconnection, dust and abnormality of a thermistor 11 from the value of resistance. The disconnection is detected at 50 deg.C and dust is detected by a circuit 36 when operation is continued and the temperature has arrived at 90 deg.C. When the operation is continued further to allow temperature rise, abnormality is detected by the thermo circuit 37 at 110 deg.C. The thermo circuit 37 consists of an operational amplifier 28, a resistor, a transistor 33, a relay 34 and the like and the circuit 37 will never cause malfunction or runaway by external noise, radio wave in air or noise, therefore, it is a safe circuit. On the other hand, the circuit 37 is provided with no contact; therefore, there may be no faulty contact due to dust. |
