Variable Pole Distance Capacitive Sensor

Variable distance capacitive sensor is widely used in industry, scientific research, and daily life due to their high sensitivity and ability to directly measure minute displacements. The core principle of their application lies in converting various physical quantities (such as pressure, force, vibration, etc.) into displacement between the plates, and then detecting the change in capacitance.

I. Measuring Minute Displacement and Vibration

This is the most direct application. The sensor directly measures the displacement, position, or vibration amplitude of an object.

Application Examples:

• Precision Shaft Displacement Measurement: Measuring the radial runout or axial displacement of a rotating shaft.
• Vibration Measurement: Used to measure the vibration amplitude and frequency of equipment like engines, turbines, and machine tools. Its non-contact nature does not affect the motion of the measured object.
• Material Deformation Research: Measuring the minute deformation of materials under stress in laboratory settings.

II. Pressure and Force Measurement

The measured pressure or force is converted into displacement via an elastic element (such as a diaphragm or Bourdon tube).

Working Principle: The moving plate of the sensor is an elastic diaphragm. When the pressure changes, the diaphragm deforms, altering the distance to the fixed plate, thereby allowing pressure measurement.

Application Examples:

• Pressure Sensors/Transmitters: Widely used in process control, aerospace, and for measuring intake manifold pressure in automotive engines.
• Differential Pressure Flow Meters: Calculating fluid flow rate by measuring the pressure difference across a restriction element.
• Weighing Systems: Converting weight into a force, which is then measured by the capacitive sensor.

III. Acceleration Measurement

Based on Newton's second law, acceleration is measured by detecting the displacement caused by inertial force.

Working Principle: The "moving plate" of the sensor is a proof mass supported by a cantilever beam. When the sensor accelerates, the inertial force causes the mass to displace, changing the capacitance between it and the fixed plates. Acceleration is obtained by detecting this capacitance change.

Application Examples:

• MEMS Accelerometers: This is one of the most successful applications. Accelerometers in smartphones, game controllers, drones, and automotive airbag systems mostly use differential capacitive structures based on MEMS technology. They are small, low-cost, and reliable.
• Industrial Equipment Vibration Monitoring: Used for predictive maintenance, monitoring the vibration acceleration of large equipment.

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