Speed detecting apparatus including a multi-coil device

Apparatus for detecting the speed of a moving object in an environment exposed to primary magnetic flux fields and secondary external magnetic flux fields, comprising:

• means for inducing at least two electric currents, one of said electric currents corresponding to the speed of the object and one of said electric currents for offsetting the effect of the magnetic flux from the external flux sources on the induced electric currents, including
• magnetic means, including at least a first and a second magnet, for generating the primary magnetic flux fields,
• multi-coil means, including at least two coils, including a first coil and a second coil, exposed to the primary magnetic flux fields for carrying the induced electric currents, for generating at least two speed signals induced responsive to the primary magnetic flux field and at least two error signals induced responsive to the secondary external magnetic flux fields, said first and second coils respectively being positioned adjacent said first and second magnets, said magnetic means being fixed in position relative to said multi-coil means and said first coil and said second coil being simultaneously movable relative to said first and second magnets and being positioned adjacent said secondary external magnetic flux fields,
• error correction circuit means for offsetting the effect of the magnetic flux from the external magnetic flux sources on the induced electric currents, said error correction circuit means including a circuit for combining the induced speed signals, said combining circuit including a frequency characteristic correction circuit corresponding to each coil, each said frequency characteristic correction circuit including an operational amplifier, a first resistor, and an integrating circuit;
• and
• support means for supporting the multi-coil means and the magnetic means and for allowing relative movement there-between, the movement corresponding to the movement of the object.