Transmissive optical sensor vs retro-reflective optical sensor | Difference between transmissive optical sensor and retro-reflective optical sensor
This page compares transmissive optical sensor vs retro-reflective optical sensor and mentions difference between transmissive optical sensor and retro-reflective optical sensor.
What is optical sensor?
• The method of sensing light rays is known as optical sensing The sensor type used for optical sensing is known as optical sensor.
• Optical Sensor converts light rays into electrical signal. This is similar to the function performed by photoresistor.
• In general, there are two components in optical sensing viz. transmitter (i.e. optical source such as LED) and receiver (optical detector such as photodiode or photo-transistor).
• Optical sensors are categorized into transmissive and reflective (or retro-reflective) types.
• Refer optical sensor basics and types >>.
Transmissive optical sensor
• The figure depicts transmissive optical sensor.
• It uses pair of components viz. one emitting light and the other receiving it. Both light emitter and light detector face each other across a small gap and are contained in a single module.
• The sensor is triggered if an object interrupts or reflects the light beam.
• It is also known as through-beam sensor.
Following are the popular transmissive optical sensors.
• Vishay TCZT8020, houses infrared LED as light source and phototransistor as detector.
• Omron EE-SX
Retro-reflective optical sensor
• The figure depicts retro-reflective optical sensor.
• It consists of a light emitter and a light detector, but they are placed adjacent to each other, facing in the same general direction.
• When both the transmit part and receive part are mounted in one single module, it is known as retro-reflective sensor. It is triggered in one of the following two ways.
➨1. An object passing in front of the light beam reflects it back to the detector. The object must be naturally reflective or must have a reflective patch applied to it.
➨2. A stationary reflector can be mounted opposite the light emitter in which case a detector beside the light emitter is triggered when the object interrupts the reflected light beam.
Following are the popular retro-reflective optical sensors.
• Rodan RT-530
• Optek OPB606A
• Vishay TCRT5000
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