Apparatus for determining the position of a switch and for monitoring the associated line for interruptions and short circuits

In an apparatus for use in determining the position of a switch connected to a two-wire line and for monitoring the two-wire line for interruption and short circuit disturbances, the apparatus including at least one generator with an output test signal having a waveform of periodically changing amplitude, the two-wire line connecting the generator to the switch for transmitting the test signal thereto, the apparatus delivering signals indicating switch position and the presence of a disturbance, the improvement in which the waveform of the output test signal of the generator has flanks with finite slopes and further comprising:

• threshold means coupled to the switch for providing an output signal responsive to switch position, the threshold means including a plurality of threshold circuits assigned to respective positions of the switch and having different threshold levels for permitting current flow at different voltage levels of the same polarity of the two-wire line, whereby the time current flows at the output of the threshold means during a cycle of the output test signal of the generator is representative of switch position and of disturbances in the two-wire line;
• means including a trigger circuit coupled to the output of the threshold means for evaluating the output signal thereof and emitting an output signal representative of the time current is present at the output of the threshold means.