A Complete Guide on Capacitive Proximity Sensor

A proximity sensor is a non-contact sensor that detects the presence of an object (also known as the “target”) when it enters the sensor’s field of view. The sensor may detect a target via sound, light, infrared radiation (IR), or electromagnetic fields, depending on the type of proximity sensor. Phones, recycling factories, self-driving cars, anti-aircraft systems, and assembly lines all employ proximity sensors. There are several different types of proximity sensors, and each detects targets in a different way. 

In this blog, we discuss the capacitive proximity sensor working principle, its advantages, disadvantages,& its applications in industries, and their use for commercial purposes.

What is a Capacitive Proximity Sensor?

Capacitive proximity sensors are non-contact devices that can detect the presence or absence of virtually any object, regardless of its material. They make use of capacitance’s electrical property and the change in capacitance caused by a change in the electrical field around the sensor’s active face.

Capacitive sensing technology is often used in other sensing technologies such as:

  • flow
  • pressure
  • liquid level
  • spacing
  • thickness
  • ice detection
  • shaft angle or linear position
  • dimmer switches
  • key switches
  • x-y tablet
  • accelerometers

Capacitive Proximity Sensors detect changes in the capacitance between the sensing object and the Sensor. The number of capacitance changes based on the detecting object’s size and distance. A typical capacitive proximity sensor looks like a capacitor with two parallel plates, with the capacity of the two plates being sensed.

The object being measured (with an imaginary ground) is on one plate, and the sensor’s sensing surface is on the other. It detects any differences in capacity generated between these two poles. The object’s detection is determined by its dielectric constant, which includes glue and water in addition to metals.

Major Features of Capacitive Proximity  Sensors

Hysteresis is a key operating feature for both capacitive and inductive proximity sensors. The difference between the sensing face and target detection distance, as well as the sensing face and target release distance, determines hysteresis. 

These characteristics define the boundary between object detection and non-detection. Despite their resemblance to inductive sensors, capacitive sensors have several distinguishing characteristics, including:

  • The ability to detect nonmetallic objects.
  • The ability to detect small lightweight objects that cannot be picked up by mechanical limit switches.
  • A solid-state output that does not bounce its contact signal.
  • A high switching rate provides a quick reaction in object counting applications.
  • The ability to detect liquid targets through certain barriers.
  • A long operational lifespan.

Capacitive Proximity  Sensors Components

  • Sensor Housing: This portion of the sensor provides the means for mounting and protecting sensor internals
  • Sensing Face: The capacitive field created by the sensor emanates from here
  • Mounting Nuts: Supplied with each sensor. For smooth tube sensors, a clamping bracket is provided
  • Sensor Endbell: Indicator LEDs typically appear in this área of the sensor
  • Connection Interface: A sensor may be equipped with a factory-installed cable, cordset, or the built-in pin connector

Capacitive Sensing Range

The sensing distance of capacitive proximity sensors is typically greater than that of inductive proximity sensors, and it ranges between 5 and 40 millimeters. Because capacitive sensors assess dielectric gaps, the detection range is determined by plate diameter. Many capacitive proximity sensors have detecting distance sensitivity adjustment settings, allowing them to accommodate the target item and application conditions.

Capacitive Proximity Sensors Working Principle

Within the capacitive proximity sensor, one plate is for the capacitor whereas the target serves as the other plate. The air gap between the sensor and the target functions as the dielectric. The plate that is internal to the sensor is connected to an oscillator circuit that is used to generate an electrostatic field.

The oscillator circuit does not trigger if the target is not there. The oscillation amplitude increases as the target approach the sensor, and when the sensor identifies the target, the amount of charge that can be stored on the internal plate changes, changing the capacitance value. When the oscillations reach a certain level, a trigger is activated, which causes the sensor to emit an output signal indicating that the sensor has been activated.

The distance between these two plates, which may be modified to achieve a specified activation range, determines the ability to hold a charge. One plate acts as a switch, the other as a detection target, and the sensor face acts as an insulator in a proximity sensor. The flipside of an inductive sensor’s parameters is that current levels fall as distance rises. Many sensors have a screw or adjustment that can be used to change the device’s sensitivity, which is handy for detecting full versus empty containers, for example.

Advantages of Capacitive proximity sensors

  • Contactless detection
  • A wide array of materials can detect
  • Able to detect objects through non-metallic walls with its wide sensitivity band
  • Well-suited to be used in an industrial environment
  • Contains a potentiometer that allows users to adjust sensor sensitivity, such that only wanted objects will be sensed
  • No moving parts, ensuring a longer service life
  • Can detect non-metallic objects, and can detect metallic objects often at greater ranges than inductive sensors
  • High switching rate for rapid response applications (counting)
  • Can detect liquid targets through non-metallic barriers (glass, plastic)
  • Long operating life, solid-state output for “bounce-free” signals

Disadvantages of Capacitive proximity sensors

  • Relative low range, though incremental increase from inductive sensors
  • Higher price as compared to inductive sensors
  • Can be impacted by ambient temperature, humidity, and moisture conditions
  • Not as repeatable as inductive proximity sensors

Hope this blog helps you to understand the basics of Capacitive proximity sensors, their working, applications, and advantages and disadvantages. We, MATHA ELECTRONICS will come back with more informative blogs.

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