Assume that a DC milliammeter is patched into a neutral telegraph
circuit that uses a telegraph line relay.
The teletypewriter runs
open while the meter indicates a steady value of current.
condition indicates that the
line relay contact points are resting on the mark contact.
relay has been removed from its socket.
circuit is transmitting a steady space.
wire pair is inverted.
Assume that a technical controller patches a DC milliammeter or
digital distortion test set into a monitor (MON) jack of a telegraph
circuit. The effect of this patch on the circuit is that the signals
are removed from the circuit because the plug on the meter patch
cord lifts the power source from the circuit.
cannot pass the meter because the meter opens the circuit.
pass through the meter, and traffic flow is unimpeded.
terminates in the meter and goes no further.
The WECO Concept is found in older DCS stations, while the H-500
concept is found in newly installed stations. One difference between
the two concepts is that the H-500 uses patch cords having
twin plugs for all VF patching.
two-contact plugs for DC patching.
three-contact plugs for RF patching.