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Proximity Switches


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Autonics inductive 12mm proximity switch
Pepperl-Fuchs inductive limit-style proximity switch
Autonics inductive 18mm proximity switch
P+F ultrasonic proximity switch
Pepperl-Fuchs 30mm capacitive proximity switch Carlo Gavazzi flat pack inductive proximity switches
Pepperl-Fuchs capacitive flat pack proximity switch
P+F ultrasonic proximity switch
When an application calls for detecting a metallic target that falls within an inch of the sensing surface, inductive proximity sensors are apt for the task. First introduced in the early 1960s, these durable components have proven their mettle in the sensing arena. In fact, they're the best-selling sensing technology in the world. Their immunity to dust and dirt buildup suits them well for harsh industrial environments. Additionally, the standardized physical and electrical characteristics of the general-purpose, cylindrical types of these sensors simplify their use.

An inductive proximity sensor has four components: the coil, oscillator, detection circuit, and output circuit. The target material, environment, and mounting restrictions all have an influence on these items and on the senor's operation, magnetic nature, and shielding. The oscillator generates a fluctuating, doughnut-shaped magnetic field around the winding of the coil, which is located in the device's sensing face. When a metal object moves into the sensor's field of detection, Eddy currents build up in the object, magnetically push back, and finally dampen the sensor's own oscillation field. The sensor's detection circuit monitors the amplitude of the oscillation and, when it becomes sufficiently damped, triggers the output circuitry.

There are five categories of inductive proximity sensors: cylindrical, rectangular, miniature, harsh environment, and special purpose. Cylindrical threaded-barrel sensors account for 70% of all inductive proximity sensor purchases. Years ago, this style's behavior was standardized by the CENELEC organization, which determined characteristics such as body size, sensing distances, and output levels.

Capacitive proximity switches contain 4 main components: plate, oscillator, detection circuit and solid state switch. The sensor operates in a similar fashion to a simple capacitor.When the power is turned on, the oscillator detects the amount of capacitance between the external target and the metal plate in the sensor. As the target approaches, the capacitance increases. When the capacitance reaches a certain point, the oscillator begins to operate (the opposite of inductive sensors, in which the oscillator stops operating when the target approaches). Once the oscillation reaches a preset point, the detection circuit senses this, and signals the switch to change state.

A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When a potential difference (voltage) exists across the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the conductors. The effect is greatest when there is a narrow separation between large areas of conductor, hence capacitor conductors are often called plates. An ideal capacitor is characterized by a single constant value, capacitance, which is measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. In practice, the dielectric between the plates passes a small amount of leakage current. The conductors and leads introduce an equivalent series resistance and the dielectric has an electric field strength limit resulting in a breakdown voltage.

A Capacitive Proximity Switch is a good choice to detect level, waer or even solids such as plastic pellets for injection molding. They are also used on sight glass tubes for level detection on bulk liquid storage tanks. The sensor will ignore the sight glass itself and detect the liquid inside of it, providing feedback for the liquid level in the bulk tank. More often, however, the capacitive sensor is used as a replacement sensor for applications ill-suited to photoeye detection. Photoelectric sensors have difficulty with materials that are dark, highly reflective, or clear, but a capacitive sensor ignores all these properties. Unlike the inductive proximity sensor, which only detects metals, capacitive sensors function as efficient, all-purpose sensors to detect nearly any material.


Both Inductive and Capacitive Proximity can both be termed as NAMUR switches. NAMUR switches are designed to be used in hazardous locations with very low voltage requirements.

NAMUR capacitive sensors are designed for use in hazardous areas. Our NAMUR sensors are ATEX approved. NAMUR sensors are also FM (Factory Mutual) approved for use in potentially explosive atmospheres.

NAMUR inductive proximity sensors are low energy devices designed for use in hazardous areas. When connected to intrinsically safe approved switch isolators, NAMUR inductive proximity sensors are approved for all hazardous area classifications.

NAMUR (Normenarbeitsgemeinschaft für Mess- und Regeltechnik in der Chemischen Industrie)

DIN EN 60947-5-6




Ultrasonic sensors (also known as tranceivers when they both send and receive) work on a principle similar to radar or sonar which evaluate attributes of a target by interpreting the echoes from radio or sound waves respectively. Ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor. Sensors calculate the time interval between sending the signal and receiving the echo to determine the distance to an object.

This technology can be used for measuring: wind speed and direction (anemometer), fullness of a tank and speed through air or water. For measuring speed or direction a device uses multiple detectors and calculates the speed from the relative distances to particulates in the air or water. To measure the amount of liquid in a tank, the sensor measures the distance to the surface of the fluid. Further applications include: humidifiers, sonar, medical ultrasonography, burglar alarms and non-destructive testing.

Systems typically use a transducer which generates sound waves in the ultrasonic range, above 20,000 hertz, by turning electrical energy into sound, then upon receiving the echo turn the sound waves into electrical energy which can be measured and displayed.

The technology is limited by the shapes of surfaces and the density or consistency of the material. For example foam on the surface of a fluid in a tank could distort a reading.

Ultrasonic sensors are used to detect the presence of targets and to measure the distance to targets in many automated factories and process plants. Sensors with an on or off digital output are available for detecting the presence of objects, and sensors with an analog output which varies proportionally to the sensor to target separation distance are commercially available.

Because ultrasonic sensors use sound rather than light for detection, they work in applications where photoelectric sensors may not. Ultrasonics are a great solution for clear object detection and for liquid level measurement, applications that photoelectrics struggle with because of target translucence. Target color and/or reflectivity don't affect ultrasonic sensors which can operate reliably in high-glare environments.


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