| 摘要 |
PURPOSE:To secure an automatic change of the reference voltage and thus to realize the detection of the return signals regardless of the variation of the number of terminals by switching the input resistance of the reference voltage generator in accordance with the change of the voltage level of the return signals to the central control unit from the terminal unit. CONSTITUTION:The current mode signals containing the return signals are converted into the voltage and then supplied to one terminal of comparator A2 via positive polarity current amplifier A1 to be compared with the reference voltage given from reference voltage generation amplifier A3. In case the level of the false return signal other than the return signal is higher than the reference voltage, the false return signal is delivered from transistor Tr2 in the period except for the generation period of gate signal SG. This signal sets counter COUN2, and decoder DEC11 turns on and off Tr3-17 ia the strobe signals generated from AND circuit AND2 with every 3 units of the gate signal to increase gradually the input resistance of amplifier A3. Thus, the reference level is heightened. And if this level becomes higher than the -terminal input voltage to be supplied to comparator A2, Tr2 delivers no false signals but does the return signals. |
