| 摘要 |
PURPOSE:To perform highly reliable maintenance, by comparing the voltage of a comparing voltage generating circuit and the voltage of a sensor. CONSTITUTION:A voltage V1 from a sensor 1 is compared with a comparing voltage V3 from a comparing-voltage generating circuit 15 in a differential amplifier circuit 9. When the voltage V1 is larger than V3, a voltage from a power source E3 is sent to an input port 11. The fact that a medium is not present in the sensor 1 is recognized with a processor 12. The processor 12 gives instructions to the circuit 15 through an output port 14 on the basis of the instructions of an instructing means 13 so that the voltage V3 is change stepwise. Thus the voltage is sequentially changed from a low voltage value to a high voltage value. Data, which are inputted into the port 11, are monitored. The value of the comparing voltage, which is increased stepwise, and at which the signal of the sensor 1 or 5 that is selected with the port 11 erroneously recognizes the presence of the medium, is checked. The result is stored, e.g. in a memory. Since the value of the voltage of the circuit 15 is increased stepwise by the means 13, the processor 12 can find the allowance of the medium detecting sensitivities of the sensors 1 and 5. In this way, highly reliable maintenance can be carried out efficiently.
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