Detection of telephone circuit loop state - employing Hall effect cell in magnetic circuit of detector coils

摘要

In a telephone subscribers line equipment the state of the loop is sensed by a Hall effect cell which is inserted into the magnetic circuits of detector windings. This arrangement enables the detector circuit to be decoupled from the line circuit. Two detector coils are each connected to the connecting wires between the subscribers equipment and telephone line terminals. A Hall effect cell is mounted in a gap in the magnetic circuit coupling two detector coils. A threshold level circuit output gives the loop state. This threshold circuit gives a high ratio between switch on a switch off states of the magnetic field.