| 摘要 |
<p>PROBLEM TO BE SOLVED: To accurately detect the existence of a medium for a long period of time. SOLUTION: A medium detecting device is provided with a sensor output storing means 34 for storing electric signals V01 and V02 outputted form a photosensor 10 when a medium P exists or does not exist; comparing and determining means 31 and 32 for determining whether a difference between the electric signals stored in the sensor output storing means 31 is smaller or not than a set value Vs; dynamic range increasing means 31 and 32 for changing, when the difference between the electric signals is determined to be smaller than the set value, the resistance value of the limit resistance section 15 or a light emitting side and/or the load resistance section 16 of a light receiving side and increasing the difference between the electric signals more than the set value; and threshold setting means 31 and 32 for setting, when the difference between the electric signals is larger than the set value, a threshold value Vth based on the sizes of the electric signals.</p> |
