SENSORS

What is a Capacitive Sensor (Capacitive Proximity Sensor)?

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A capacitive sensor is a non-contact proximity sensor used to detect the presence or level of metallic and non-metallic materials. It works by creating an electrostatic field and detecting changes in capacitance when a material enters the sensing area. Capacitive sensors can detect materials such as liquids, powders, granules, plastics, glass, wood, paper and metals, making them particularly useful for product detection and level monitoring in industrial automation. In suitable applications, they can also detect materials through non-metallic walls, allowing liquids or bulk materials to be monitored from outside a plastic or glass container.

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This is the major difference from an inductive proximity sensor, which is primarily designed to detect metal objects.​

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How does a capacitive sensor work?

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A capacitive sensor creates an electrostatic field at its sensing face. When an object enters this field, it changes the capacitance detected by the sensor. Once that change reaches a predetermined threshold, the sensor switches its output and sends a signal to a PLC, controller or other automation system.

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Because capacitive sensors respond to changes in dielectric properties, they can detect a wide variety of materials, including:​

• Plastic

• Glass

• Wood

• Paper and cardboard

• Powders

• Granules

• Liquids

• Oils

• Chemicals

• Food products

• Metals​

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A major advantage: detecting through containers.

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One particularly useful feature of capacitive sensors is their ability, in suitable applications, to detect materials through non-metallic container walls.

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For example, a capacitive sensor mounted outside a plastic or glass tank can potentially detect whether liquid is present inside without coming into direct contact with the liquid.

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This makes them useful for level detection.

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Common industrial applications

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Capacitive sensors are frequently used for presence detection, level monitoring, counting and product detection in applications such as packaging machinery, food and beverage production, plastics manufacturing, agriculture, chemical processing and general factory automation.

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Examples include detecting whether powder is present in a hopper, monitoring liquid level in a plastic tank, detecting cardboard boxes on a conveyor, detecting plastic components, and checking whether a container has been filled.

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Capacitive vs inductive sensor

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The easiest distinction is:

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Inductive sensors detect metallic objects.
Capacitive sensors can detect metallic and non-metallic objects, including liquids, powders and plastics.