How Capacitive Proximity Sensor Works?

Capacitive Proximity Sensor Control Technology Proximity Sensor
Capacitive Proximity Sensors detect all materials, including liquids, powders and metallic and non-metallic solids. These sensors are often used to control the levels of pellets, liquids and powders in production control. Like their inductive counterparts, they are manufactured in shielded and non-shielded configurations and are available in both AC and DC power formats. The shielded models are used to detect solid products such as cartons, stacks of paper, wood or liquids through the wall of a non-metallic container. The non-shielded models are used to detect liquids or powders where the product flows around the sensor. Shielded models have a shorter detection range since part of the field is lost in the shielding process. All detection ranges given on the following pages are for a steel target which is equal to, or larger than the diameter of the sensor. Non-conductive products, such as wood or plastic, will be detected at a reduced detection range. The range at which a product is detected is directly related to the dielectric constant of the material; the greater the dielectric constant, the greater the detection range
Shielded Configuration: Non-shielded Configuration: Shielded sensors have a straight-line electrical field. They scan for the presence of solids (e.g. wafers, components, PCB’s, hybrids, cartons, bottles, plastic blocks and stacks of paper) at a distance. Shielded capacitive sensors can also detect liquids through a separating wall (glass or plastic up to a maximum of 4mm thick). Non-shielded sensors have a spherical electrical field. They are designed to touch the product with their active surface. They are used to detect mainly bulk goods or liquids (e.g. granulate, sugar, flour, corn, sand, oil, water or pastes).
Sensitivity Adjustment All capacitive models have an adjustable sensitivity that allows the calibration to be made in the field. This allows the sensitivity to be set for the target desired; for example, the sensitivity can be reduced to ignore a glass container but still detect the liquid inside the container. Similarly, the sensitivity can be reduced to ignore a build-up of a viscous product such as honey while still detecting the level when a large amount of the product reaches the sensor. To adjust the sensitivity on a Capacitive Proximity Sensor, mount the sensor in the working position. Allow the target material to reach the position where detection should take place. If the material has not been detected, rotate the sensitivity potentiometer clockwise, with the screwdriver provided, until detection first occurs (LED will illuminate). Continue to rotate the potentiometer for another 1/4 turn. Remove the target material and ensure that the sensor turns OFF (LED will turn off). If the sensor turns OFF, leave the sensitivity at that position. If the sensor remains ON, decrease the sensitivity (counterclockwise rotation) until the sensor turns OFF. For best results, position the sensitivity potentiometer half way between these two points.
Capacitive Sensor Oscillator Circuit Capacitive proximity sensors consist of an RC-oscillator with a special multi-part sensing electrode. The electrode and the oscillator circuit have a tube connected with earth potential for lateral shielding. This enables flush mounting of sensor in metal, since the electrical field is only present in front of the sensing electrode. This field is the active zone of the sensor. When the conductive material is removed from the active zone, the oscillator is undamped and the oscillation amplitude decreases. The amplifier os the oscillator voltage and the sensitivity of the sensor can be altered by the built-in potentiometer. The middle electrode together with the built-in re-coupling gives very effective compensation under conditions of humidity, dust or icing. Special circuitry automatically compensates for these influences. The preset sensing distance remains nearly constant. The electrode design, along with the compensating circuitry of capacitive sensors, is a unique design, and provides performance advantages far superior to other capacitive sensors.
Capacitive Switch Block Diagram
Applications for Capacitive Proximity Sensors
Liquid Level Control		Carton Detection		Bin Level Control		Resist Liquid Level
Capacitive Proximity Sensors reliably detect liquid levels.		The packaging industry relies on Capacitive sensors to detect paper and cardboard cartons.		Capacitive Sensors can detect liquids, powders, plastic pellets and pastes for level control.		Use Capacitive Sensors to monitor resist liquid levels in pipes.