| 摘要 |
<p>The thermistor timing circuit for inward dialling in branch telephone exchanges comprises a series circuit consisting of a diode, thermistor (HL), zener diode (ZD) and relay coil (MS). A Zener diode is placed in series with the thermistor so that the timing interval of the circuit - due to the response curve of the thermistor - is kept within closely defined limits, and does not vary widely due to changes in the ambient temperature within the equipment. The zener characteristic is chosen so as to flatten the thermistor characteristic so that at normal temperature, the delay characteristic of the timing circuit are maintained at the upper limit and at higher temperature, at the lower limit with the same voltage.</p> |
