Security circuit for DC powered vehicle lamps - uses coils in series with lamps to produce null field till fault occurs, unbalancing field and actuating warning circuit

摘要

The security circuit uses a pair of coils, each in series with a lamp, arranged so that the fields of the coils are opposing. If both lamps are functioning correctly the two fields are equal and opposite. A magnetic field transducer (36) is placed between the two coils, and actuates a contact (37) if a non-null field exists. This contact supplies a warning lamp (38,39,40) to indicate the failure. If lamps are symmetrically disposed then the coils are in series with the lamps, while if the lamps are asymmetric a resistor of the same value as the lamp resistor is used to balance the magnetic detector circuit.