| 摘要 |
PURPOSE:To maintain an output voltage constant over a wide temperature range by controlling the conductance of a variable conductance circuit with an amplified output of a minute DC voltage generated due to the temperature change of a detecting head. CONSTITUTION:A minute DC voltage resulting from the change in coil resistance caused by the temperature change in the coil of a detecting head 1 is generated between the terminals of the capacitor of a resistance change detecting circuit 2. This DC voltage is inverted and amplified by a DC voltage amplifier 3 and then, the amplified voltage is applied to the base of the transistor of a variable conductance circuit 4. Consequently, the base current of the transistor decreases and, apparently, the Q-value of a high-frequency circuit including the coil of the detecting head 1 decreases through a change similar to the negative temperature coefficient change. Consequently, the increase in the output voltage of the detecting head 1 is counterbalanced. Therefore, the output voltage of a detecting head can be maintained substantially constant over a wide temperature range, even if the detecting head is very small. |
