A high voltage bushing including a voltage grading shield in two parts. The method comprises receiving a design and building an intermediate binary decision diagram for the design containing one or more nodal binary decision diagrams. Information stored within and specific to the microprocessor is accessed. If a match is obtained between the entered and expected vehicle identifiers, the vehicle identifier is sent from the production control system to a vehicle Immobilizer. In that the lower frequency at which signal processing is performed is a fixed frequency, many sensitive parameters of the band pass filters, such as gain and phase shift, can be easily calibrated and do not change during operation, resulting in a simpler calibration process and very accurate data measurements.