Proximity sensor type and working principle

Inductive & CapacitiveTheir operating principle is based on a high frequency oscillator that creates a field in the close surroundings of the sensing surface. The presence of a metallic object (inductive) or any material (capacitive) in the operating area causes a change of the oscillation amplitude. The rise or fall of such oscillation is identified by a threshold circuit that changes the output state of the sensor. The operating distance of the sensor depends on the actuator's shape and size and is strictly linked to the nature of the material (Table 1 & Table 2.). A screw placed on the back of the capacitive sensor allows regulation of the operating distance. This sensitivity regulation is useful in applications, such as detection of full containers and non-detection of empty containers.
Table 1: INDUCTIVE SENSORS Sensitivity when different metals are present. Sn = operating distance. Fe37 (iron) Stainless steel Brass- bronze Aluminum Copper 1 x Sn 0.9 x Sn 0.5 x Sn 0.4 x Sn 0.4 x Sn	Table 2: CAPACITIVE SENSORS Sensitivity when different materials are present. Sn = operating distance. Metal Water Plastic Glass Wood 1 x Sn 1 x Sn 0.5 x Sn 0.5 x Sn 0.4 x Sn
Photoelectric These sensors use light sensitive elements to detect objects and are made up of an emitter (light source) and a receiver. Three types of photoelectric sensors are available. Direct Reflection - emitter and receiver are housed together and uses the light reflected directly off the object for detection. Reflection with Reflector - emitter and receiver are housed together and requires a reflector. An object is detected when it interrupts the light beam between the sensor and reflector. Thru Beam - emitter and receiver are housed separately and detects an object when it interrupts the light beam between the emitter and receiver. Magnetic Magnetic sensors are actuated by the presence of a permanent magnet. Their operating principle is based on the use of reed contacts, which consist of two low reluctance ferro-magnetic reeds enclosed in glass bulbs containing inert gas. The reciprocal attraction of both reeds in the presence of a magnetic field, due to magnetic induction, establishes an electrical contact.