A basic capacitive proximity sensor detects objects by measuring changes in capacitance. Capacitance is a property that describes the ability of a capacitor (a component that stores electrical charge) to store an electric charge between two conductive surfaces. When an object comes close to the proximity sensor, it changes the capacitance between the sensor and the object, and this change is used to detect the presence or absence of the object.
Here's how a basic capacitive proximity sensor works:
Sensing Area: The capacitive proximity sensor has a sensing area, usually a conductive surface or electrode. This sensing area is where the capacitance change will be measured.
Oscillator Circuit: Inside the sensor, there is an oscillator circuit. The oscillator generates an alternating electric field around the sensing area.
Baseline Capacitance: When no object is present in the proximity of the sensor, the electric field's capacitance is at a baseline level. This baseline capacitance is stable and represents the sensor's default state.
Change in Capacitance: When an object (such as a human hand, metal, or any conductive material) comes near the sensor, it interacts with the electric field and changes the capacitance. This is because the object has its own capacitance, and it acts as an additional plate of a capacitor in conjunction with the sensor's sensing area.
Frequency Shift: The change in capacitance affects the frequency of the oscillator circuit. When the capacitance increases due to the presence of an object, the oscillator frequency decreases, and vice versa.
Detection: The sensor's electronics detect this change in frequency. If the frequency falls below a certain threshold or crosses a predefined value, the sensor interprets this as the presence of an object in the proximity.
Output: The sensor provides an output signal, which can be either analog or digital, to indicate the presence or absence of an object.
Capacitive proximity sensors are commonly used in various applications, including touchscreens, object detection in industrial automation, liquid level sensing, and more. They offer several advantages, such as non-contact sensing, high reliability, and resistance to environmental factors like dust and moisture. However, they may have limitations in detecting non-conductive objects or objects with low dielectric constants. To overcome such limitations, more sophisticated capacitive sensors with additional features are used in specific applications.