Electromagnetic position sensor
Electromagnetic position sensors use electromagnetic effects to achieve their position measurement, mainly open transformer type, resonance type proximity switch and so on.
The open transformer position sensor consists of two parts: the stator and the rotor. The stator can be laminated by punching silicon steel sheets, or pressed by high-frequency ferrite materials. The open transformer stator in the 2-pole three-phase brushless DC motor has six teeth, and the interval between them is 60°. Three of the teeth are wound with the upper primary winding, and are connected in series with each other and then are powered by a high-frequency oscillating power supply (generally several kilohertz to tens of kilohertz); the other three teeth are respectively wound with secondary windings, and they are separated from each other. 120° apart. The rotor is a disc made of non-magnetic material, and a sector-shaped magnetic material of about 120° is inlaid on it. Install it coaxially with the motor. The working principle of the split transformer is similar to that of a general resolver. The output of the three secondary windings is a high-frequency signal modulated by the rotor position, which is demodulated and then processed by logic to obtain the commutation control signal.
The structure of the resonant proximity switch position sensor is similar to that of an open transformer, but it does not require high-frequency excitation on the primary side. In a three-phase motor, its stator has a resonant circuit composed of three inductance elements, and the rotor is a sector-shaped conductive metal disk of about 120°. When the sector-shaped metal part of the rotor is close to the inductance element, the quality factor Q of the circuit decreases. , Resulting in insufficient positive feedback of the circuit and stop vibration, so the output is zero. When the fan-shaped metal rotor leaves the inductance element, the Q value of the circuit starts to rise, and the circuit re-oscillates to output a high-frequency modulation signal. The output of the three resonant circuits is a high-frequency signal modulated by the rotor position, which undergoes logic processing after detection and demodulation to obtain the rotor position signal.
Electromagnetic position sensor has the advantages of reliable operation and adaptability to harsher environment. However, this kind of sensor has low signal-to-noise ratio, poor position resolution, and large volume, so it has been rarely used.
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