○The mechanical quantity to be measured, such as displacement, pressure change into an electrical capacitance sensor.
Therefore, capacitive sensors can be divided into pole pitch change type, area change type, change the media type categories. Pole pitch change type is generally used to measure the tiny lines or due to force displacement, pressure, vibration caused by the pole pitch changes (see capacitive pressure sensor). Area change type is generally used to measure the angular displacement or larger linear displacement. Change media type commonly used in level measurement and a variety of medium temperature, density determination and humidity.
○The induction surface of capacitance sensor is composed of two coaxial mental electctrodes, which from a capacitor and connected on RC oscillation circuit, just like an open capacitor electrode.
○When connecting to power supply, RC oscillator does not work. When an object is clos eto capacitor
electrode, the capacitor capacity will increase, and the oscillator will vibrate. Through the treatment of behind stage circuit, both signals of stop oscillation and oscillation will be converted to switch signs for checking the existence of object. this distance can be obtained, but to nonmetal object, the action distance is d etermined by material dielectric constant, the more dielectric constant, the more action distance will be obtained.
1. Compact volume, High on-off frequency
2. Good performance of anti-interference
3. Many output forms, Wide voltage range
4. Dust proof, vibration proof, water proof and oil proof
5. connecting protection
6. Long service life
The dielectric constants for some important materials are as:
|Materials||Dielectric constant||Materials||Dielectric constant||Materials||Dielectric constant||Materials||Dielectric constant|
|Synthectic resin adhesive||3.6||Styrence||3||Alcohol||25.8||Polyvinyl||2.9|
|Marble||8||Quartz sand||4.5||Cable rubber compound||2.5|