| 摘要 |
PURPOSE:To avoid the effect of the DC polarizing function as well as to receive no limitation for the circuit design, by selecting optionally the frequency and the level of the signal which is applied to a heat-sensitive material. CONSTITUTION:A heat-sensitive material 3 and a resistance 7 are connected to a high frequency signal source 6 via electrodes 2 and 4 together with a resistance 8 and a temperature setting variable resistor (volume) 9. The joint between the material 3 and the resistance 7 as well as the joint between the resistance 8 and the volume 9 are supplied to a comparator 10. The comparator 10 compares the temperature setting signal with the temperature detecting signal and delivers them. A control circuit 11 works in response to the comparison output signal of the comparator 10 and controls the conduction of a switching element 12 and then the conduction of a heater 13. In such a way, the signal source frequency is set higher than the commercial frequency to set the impedance at a low level. At the same time, the signal source voltage can be set freely. This ensures a free design of a control circuit. |
