More about Proximity Sensors

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Proximity sensors are switches or sensing devices that can detect a nearby, specific object without actual contact. There are three types of proximity sensor: inductive, capacitive and magnetic. They can be either shielded or unshielded. Typically, all require close positioning to the object being sensed (about ½ inch or less). Proximity sensors require almost no maintenance, and most are resistant to environmental contaminants and conditions.

Inductive proximity sensors react to metal objects placed near the sensor, while capacitive switches are able to detect both metals and non-metals. Capacitive proximity sensors are even able to detect airborne particulate, and can function when obstructed by metallic and non-metallic barriers. Certain proximity switches can be designed to operate in harsh conditions, such as corrosive or hazardous chemicals or extreme heat and cold. Basic magnetic proximity sensors contain a hermetically sealed reed switch that detects nearby objects. Applications include liquid metering, event cataloging and positioning for a wide variety of items.

When selecting a proximity sensor, it is important to consider its operating distance and the object(s) being sensed. In many cases, the sensing distance varies with the object being sensed. Inductive proximity switches, for example, have different sensing distances for different metals. The sensing range typically listed for a sensor may not be accurate in certain environments or for certain materials, although most manufacturers can supply accurate information when the sensed material is specified. In addition, some switches allow shielding, while others cannot function when mounted near metal; metal objects can interfere with some proximity sensors even when found outside the normal sensing range.

Also of importance when choosing a proximity sensor is the electrical nature of the system in which it is placed. The sensor must function with the system controls and allow for necessary integration. They may be used to signal or record various events, such as notifying a control system when an object is too close, or cataloging the amount of times a given object came within range of the sensor.