The variable reluctance sensor consists of a wire wrapped around a permanent magnet. When the ferromagnetic material such as a flywheel tooth passes the sensor the magnetic field is disrupted. Due to this an AC voltage is generated, the amplitude and frequency of which depends on the speed of the flywheel. Here the polarity of the voltage is not important. The amplitude of this AC voltage also depends on the air gap i.e. the distance between the sensor and the flywheel tooth. The voltage decreases as the air gap increases and the voltage increases as air gap decreases. Since the amplitude depends on the speed and also the air gap, correct setting of the air gap is very important when measuring lower speeds. This AC signal from the sensor can be processed further to obtain the digital output.
The variable Reluctance sensors are called as passive sensors since they don’t need external power supply for their operation.
Advantages of Variable reluctance sensor
The variable Reluctance sensors are called as passive sensors since they don’t need external power supply for their operation.
Advantages of Variable reluctance sensor
- They don’t need external power supply
- Low cost
- Light weight
- They are robust and can work in harsh environments
- Can work in high temperature and high vibration environment
- Difficult to measure low speeds
- Additional signal processing circuitry required
- Gear tooth speed sensor
- Turbine speed of the jet engine
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