Magnetic compass with optical encoder

A vehicle compass with which heading is determined by measuring compass rotor displacement from a reference position to a position in alignment with the local magnetic field after the rotor is turned by a search coil to the reference position, said compass comprising:

• a support body comprising a cylindrical cup and a support member defining a recess at the open end of said cup,
• a compass rotor including a compass magnet, an encoder disk and pivot pins defining a rotation axis of said rotor, said rotor being disposed with the magnet in the cup and with the pivot pins supported by the bottom of the cup and the support member,
• said support member comprising a base plate and an axially spaced cover plate with said encoder disk therebetween, said base plate defining a vehicle orientation axis,
• said encoder disk having a reference aperture therein,
• each of said plates having a first optical aperture therein at a first predetermined angular position relative to said orientation axis and at the same radial position as said reference aperture,
• a transducer comprising a reference position sensor having a first optical transmitter and first optical receiver with an optical axis therebetween in alignment with the first optical apertures in said plates,
• a first retaining means on one of said plates and a second retaining means on the other of said plates for holding said first transmitter and first receiver, respectively, in said alignment with the first optical apertures,
• a support arm for a search coil on said cup opposite said magnet in a predetermined angular location relative to said orientation axis and a search coil on said support arm,
• said base plate, cup and support arm being a unitary molded body of polymeric material whereby the optical axis of said sensor and the location of said search coil have predetermined and precisely reproducible angular locations relative to said orientation axis.