Photoelectric Proximity Switches are used when higher sensing distance is desired. Through beam, retro reflective and diffuse versions are available. Fiber optic switches and proximity sensor switches are used for mark sensing and color sensing Light curtains are used as area sensors. Optical proximity switches are used where higher sensing distance is required with non contact operation. The object can be sensed by three methods; a) Diffused Reflective b) Retro Reflective c) Through Beam
These switches have a distinct advantage of higher sensing distance over Inductive and Capacitive type of switches. These can work more reliably in a noisy electromagnetic radiation environment. As an infra-red wavelength is used, it is immune to visible light interference.
These switches incorporate an infra-red transmitter & receiver device housed in a single enclosure or separate enclosures. The precision pulsed transmitter beam is interrupted or reflected by the object. The advanced electronic circuit generates an effective output signal when the object is sensed.
Through Beam Type
Through Beam (TB) type switches have separate transmitter & receiver. The object is sensed when the beam is interrupted.
Transmitter and receiver are enclosed in two separate housings. When they are aligned light beam travels from transmitter to receiver. Object breaking the light beam causes a change in the receiver. This change is detected and output signal is produced to drive external relay.
Diffused Reflective Type
Diffuse Scan /Reflection (DS) type switches have both transmitter & receiver in the same enclosure. The closely focused beam is reflected back by the object.
This is a fixed focused type of switch. Transmitter and receiver enclosed in one housing. Transmitted beam strikes on the object (when the object enters the sensing range) and gets reflected by object surface. Receiver detects these rays and output signal is produced.
Retro Reflective Type
Retro Reflective (RR) type switches use a special reflector to reflect back the beam. When an object interrupts the beam, an output signal is generated. These models have grater sensing distance compared to DS type. The receiver does not consider the reflection from the object.
Transmitter and receiver are housed in single housing and aligned with the reflector. The beam reflected by the reflector gets back to the receiver. Object breaking the light beam causes a change at the receiver. This change initiates an output signal.