Proximity sensors are used for contactless detection of presence or absence, as well as the position, direction, velocity, and physical properties of objects. The proximity sensor sends an analog or digital output which can be used for counting, sorting, automatic routing, positioning, or quality control. Proximity sensors can be divided by technology into five broad types: inductive sensors, capacitive sensors, magnetic sensors, photoelectric sensors and ultrasonic sensors, also known as radar sensors.
Proximity sensor types:
Things to consider when choosing a proximity sensor:
1. What objects need to be detected by the sensor?
Some proximity sensors can only detect metallic, magnetic or non-transparent target objects.
2. What is the distance between the sensor and the object being detected?
Maximum sensing ranges vary across sensor types, with magnetic sensors typically accurate over the greatest distance.
3. What environment will the sensor be used in?
Magnetic sensors are generally tolerant of harsh, dirty and damp environments. Inductive and capacitive sensors may be affected by corrosion. Photoelectric and ultrasonic sensors offer advanced detection capabilities, but can be disrupted by moisture, dirt, changes in pressure or temperature, background color or noise.
4. Where will the sensor be mounted and what kind of power will it need?
Photoelectric, ultrasonic, capacitive and inductive sensors typically require an external power source. Through-beam photoelectric sensors require mounting and wiring of both emitter and receiver on opposite sides of the application. Magnetic sensors may not require an external power supply. Consider also whether your sensor will need to be shielded from interference, or detect objects through a physical barrier. Miniature sensors may be required for installation within smaller devices.
5. How will the sensor transmit signals and where will those signals be transmitted?
Some sensors need a wired connection to a load device such as a PLC, while others can transmit remotely. Some proximity sensors give digital, binary outputs (presence/absence, fill above/below a threshold), while others give analog outputs (size, shape, color, label identification, continuous fill level monitoring, stack height, velocity and direction of travel, angular positioning).