Capacitive Proximity Sensors

 

Capacitive proximity sensors measure the proximity between conductive and non-conductive objects by creating an electrostatic field on a sensor face and surrounding it with a guard of equal potential. The capacitance of the sensor varies with gap distance, dielectric constant, and target surface area. Ambient air has a relatively constant dielectric constant, which makes it the most practical sensor for a wide range of applications. This article will discuss the different types of capacitive proximity sensors available and what they can be used for.

Types of capacitive proximity sensors

There are several types of capacitive proximity sensors on the market today. M30 series capacitive proximity sensors have a long sensing range. OsiSense XT series capacitive proximity sensors are designed to detect insulating materials such as plastic, glass, and metal. Besides the M30 series capacitive proximity sensors, there are many other series available in the market, such as di-sonic proximity switches. 

Ultrasonic proximity sensors are widely used in automated production processes. These sensors detect objects by emitting sound waves. Because the wavelengths are not affected by colors, these sensors are perfect for long-range detection of objects made of clear glass. They are also ideal for measuring distances, continuous fluid or granule levels, and stacking materials. They can detect small objects that may be hard to reach or too far. And they are very durable and are highly accurate.

Operation of capacitive proximity sensors

Capacitive proximity sensors detect metallic or non-metallic objects by changing the state of an oscillator circuit. When an object approaches the sensor, it enters an electrostatic field generated by the electrodes. This change in capacitance changes the amplitude of an oscillator, which then begins oscillating. The sensor's output state changes when the amplitude reaches a certain level, and it switches back to its initial state when the object moves away. Non-contact proximity sensors use an electromagnetic field to detect a ferrous object. This operation works on the principle of inductance, a fluctuating current that induces an electromotive force on a target. These sensors contain an asymmetrically tuned circuit that emits an electromagnetic field. The field is just weak enough to provide feedback and keeps the circuit going. Non-contact proximity sensors can detect both ferrous and non-ferrous objects.

Capacitive proximity sensors (CPS) are sensing devices designed to detect both metallic and non-metallic targets. They can detect lightweight or small objects that cannot be detected by mechanical limit switches.#Capacitiveproximitysensors #CPS #Electronics pic.twitter.com/tKjiHjVh0t

— Joddie Marshall (@joddie_marshall) April 6, 2022

The sensing distance of capacitive proximity sensors

One important parameter to consider when evaluating the sensitivity of a capacitive proximity sensor is the sensing distance. Capacitive proximity sensors typically have a sensing range of five to forty millimeters. The measurement of these distances can be made more accurate if the target is non-conductive, such as in the case of a metal object. Capacitive proximity sensors are also capable of compensating for a variety of application conditions, such as temperature or target object properties. A capacitive proximity sensor works by detecting an object by measuring its dielectric constant, or charge. It detects an object's presence by forming a good electrical capacitor with the sensor's internal plate. Because the dielectric strength of a material is negligible, it is easy for a capacitive proximity sensor to detect a target. The distance between the target and the sensor is the sensing distance.

Components

A capacitive proximity sensor has four main components, which can be configured in different ways. They consist of an electrode on the end face of the cylinder and a metal ring on the active sensing face. These components are combined in a circuit to produce a signal that is either voltage or contact closure. Capacitive proximity sensors can detect various levels of liquid or solid materials. The resulting signals are used in a variety of applications.