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Sensor Designs

CambridgeIC has developed a range of standard sensors, including rotary and linear in different types and sizes. They are built using conventional printed circuit board (PCB) technology. CambridgeIC supplies Sensor Blueprints to allow a customer's own PCB supplier to build sensors.  This also allows a customer to design PCBs that combine one or more sensors with other electronic circuitry. Sensors are also available as finished PCBs assembled with modular connectors for development and low-volume production.

Type 1 sensors are the simplest and comprise 3 coils.  The excitation coil (EX) is used to power the resonator, and the return signals are detected in the COS and SIN coils. The figure below shows an equivalent circuit for the sensor coupled to a resonator inside the target.
Type 1 resonant inductive position sensor block diagram
The figure below illustrates a simplified sensor coil design for a non-contact linear position sensor. Non-contact rotary sensors use a similar principle, with the coils arranged in a circle. The excitation coil is shown in black and surrounds the two sensor coils. As shown on the graph underneath, its coupling factor to the resonator is approximately constant, so that the resonator is always powered when the resonator is within the Measurement Range. The COS and SIN coils are patterned so that their coupling factors to the resonator kCOS and KSIN vary sinusoidally along the Measurement Range. This approach is also commonly used in LVDTs, RVDTs and resolvers. Sensor coils are balanced (they have portions wound in opposite directions) so that inductive interference cancels.
Type 1 sensor coil pattern and coupling factors
Type 2 and Type 6 sensors use more coils for precise measurement and/or over longer distances.

Type 3 sensors have a special coil arrangement that allows the target's magnetic axis to point along the measuring direction. This is for fluid level sensing, and other applications that require precise measurement while the target remains free to rotate.