| 摘要 |
PURPOSE:To eliminate an error due to a temperature gradient and to perform position detection with high accuracy by holding the error output due to the temperature gradient of a semiconductor position detecting element which is outputted by a differential amplifier when a light source is off, and subtracting the held error due to the temperature gradient from a position signal including an error due to a thermoelectromotive force from the amplifier when the light source illuminates by a 2nd amplifier. CONSTITUTION:The light emitting diode 1 is fitted to a body whose position is to be detected and light from this diode 1 is photodetected by the semiconductor position detecting element 2 to detect the position of the diode 1. This diode 1 is turned on or off at specific timing with the output L of a control circuit 9. When this diode 1 is off, the thermoelectromotive force of the element 2 is converted by current-voltage converting circuits 4 and 5 into a voltage, which is inputted to the differential amplifier 6 is held by a sample holding circuit 10 and added by the differential amplifier 1 and a subtracter 8 performs subtraction between a summing amplifier 7 and the amplifier 11 to eliminate an error due to variation in temperature gradient.
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