Variable Reluctance/Inductance Pressure Sensors

Reluctance is the opposition to current flow that is caused by magnetic circuits. Inductance is the property of a coil of wire to build magnetic flux lines. The amount of inductance in a coil depends on the number of turns of wire in the coil, the amount of current flowing in the wire, and the type of core that is placed inside the coil of wire or the position of a core when it's inside a coil. An easy way to change the amount of inductance in the coil is to change the position of a movable core inside the coil. The movable core can be attached to the diaphragm in a manner similar to the pressure sensors previously discussed. When the pressure moves the diaphragm, the core will move and change the amount of inductance in the coil of wire. When the amount of inductance changes, the amount of inductive reactance also changes. If the coil is placed in an ac circuit, the change of inductance can be used to change the voltage drop across the inductor or it can be used in an oscillator circuit to change the frequency of the circuit. These types of sensors are also called variable reluctance, since the opposition to inductance is called reluctance.

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