How AKA Passive Speed Sensors Work:
Variable Reluctance (Passive Speed Sensor)
- Magnetic resistance is known as reluctance (variable reluctance = VR).
- Each tooth positioned in front of the pole decreases reluctance and increases magnetic field density around the coil
- Each valley increases reluctance and causes the magnetic field to collapse around the coil thereby generating a voltage.
- Repeating combination of tooth & valley, such as found on a gear, create a sinusoidal electrical output signal.
- As the rate of change of the magnetic field increases, so does the amplitude
Variable Speed Sensors Features:
- Senses gears or any ferromagnetic discontinuity
- No moving parts or contacts
- Two Wires (No Power Req’d)
- Harsh environments (pressure or chemical)
- High ambient Temperatures – (750 F / 400 C max)
Variable Speed Sensors Benefits:
- Easy installation
- No alignment
- High reliability – mature technology
- Low Cost
Variable Speed Sensors Limitations:
- Poor low speed performance (below 100RPM / 15 IPS)
- Output amplitude dependent on speed and air gap