| 摘要 |
PURPOSE:To compensate light emission temperature characteristics of a light emitting diode and to reduce a measurement error over a wide temperature range by interposing a fixed resistance and a negative characteristic thermistor between a measurement terminal and the light emitting diode. CONSTITUTION:A signal V converted to a low voltage by a CT or PT is impressed between terminals A and B of the circuit constituted by connecting a temperature compensating circuit 1 to the light emitting diode LED in series and light from the light emitting diode is guided through an optical fiber to a photoelectric converting element and measured therein. The temperature compensating circuit 1 consists of a fixed resistance R1 with a low temperature coefficient and the parallel circuit of the negative characteristic thermistor Rt and a fixed resistance R2 with a low temperature coefficient connected to the former fixed resistance in series. For this purpose, the resistances R1, R2, and Rt are so selected that when a current flowing the light emitting diode at 25 deg.C is 100%, the current is 89% at -20 deg.C and 113% at +80 deg.C, suppressing the compensation error to <1% over the entire temperature range. |
