Photo Sensors (Essay Sample)

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Abstract
A photoelectric sensor is a device that uses beams of light to detect presence, absence or distance of an object. The major components of this kind of sensor; it has a transmitter, mostly infrared, and a receiver. They are majorly applied in industrial manufacturing processes. The various types of photoelectric sensors include; diffuse-reflective, retro-reflective, through-beam and distance-settable type. A self-contained photoelectric sensor carries out its own modulation, amplification and demodulation. It contains the optics and other electronic components. For it functionality, it only requires a source of power. Due technological advancements, the photoelectric sensor is increasingly becoming smaller. In remote sensing, a remote photoelectric sensor is used. Unlike the self-contained photoelectric sensor, a remote photoelectric sensor is composed of only the optical components. When the environment is hostile or restricted so that other photoelectric sensors are inappropriate, a fibre optic is used. The fibre optic sensor receives and transmits light rays from the object via fibre optic cable, light passages, to the control board that is located elsewhere. Fibre optic photoelectric sensor is capable detecting minute objects.
Introduction
The increase in industrial competition demanded improved efficiency in processing and manufacturing to reduce the cost of production. The invention of the photoelectric sensor is one of the techniques put in place to elevate production efficiency. The of the major characteristics of the photoelectric sensor are; non-contact detection of objects, detection with high accuracy, detection of objects at long distances, high response speed and detection of virtually any kind of object.
Principle of operation
Modulated or pulsed light increases the range of sensing while reducing the effect of the background or ambient light. The specific frequency of the light ranges between 5-30Hz. The sensor is capable of distinguish between the ambient and the pulsed light. A photoelectric sensor is made up of five basic components namely; a light source, light detector, lenses, logic circuit, and the output.
* Light source
Most photoelectric sensors make use of LED light (light emitting diode). LED emit light a specific wavelength and colour of light. LED and its circuitry is referred to as the emitter. The red visible light is the most efficient as it produces less heat. Laser source have been used in place of LED although at some additional cost. The advantage of LED is its ability to turn on and off rapidly. The lenses concentrate the light on the receiver while narrowing the area or shape covered by the light from the emitter. This process increases the distance of sensitivity of the sensor.
* Light detector
This the component that detects the radiations from the source or the reflected rays. It is composed of a phototransistor or a photodiode. The amount of light detected corresponds to the current conductance. The detector is sensitive to a certain wavelength of light. The sensitivity of the LED and light detector is improved by matching them spectrally.
* The logic circuit
The logic circuit is responsible for modulating the LED besides amplifying the signal
From the detector. It also determines whether the output will be activated or not.
* An output device is activated when sufficient light intensity is detected.
Retro-reflective
In the retro-reflective photoelectric sensor, the transmitter and the receiver are placed in the same location. An object is detected when the transmitted beams of light fail to reach the receiver. A reflector is incorporated the transmitted to bounce back to the receiver.
Pros
* It has a high level of accuracy.
* It is very reliable for its better sensing.
Cons
* The sensor must be installed on two opposite sides of the system. The sensor and the receiver
* The sensor is slightly more expensive than the diffuse type
* The sensing range is less than that of through-beam.
Diffuse photoelectric sensor
In the diffuse photoelectric sensor, the transmitter emits radiation either as visible light or as infrared that is reflected and detected by the receiver. This sensor does not utilise the interruption of light, but rather the reflected light. In the sensor, the transmitted light is pulsed. It is also referred to as the proximity photoelectric sensor. Absence of an object results in the travel of light in one direction without returning. The sensor relies on the reflectivity of the object. It is most suitable for detecting identical objects so that its performance remains reliable, and adjustment become easy to make.
Pros
* The sensor is only installed at one point, unlike the reflective type.
* It is the cheapest among the three types of photoelectric sensors
Cons
* It is the least accurate in the three types
* It requires more time in setting up the system.
Through-beam
The through-beam, otherwise known as the opposed mode, is a system consisting of a transmitter installed in line and on the opposite side of the receiver while facing each other. The light beams from the transmitter are aimed at the receiver. An object that is in the path of light prevents the receiver from receiving the light. Thus, it is activated. Since the emitter and the receiver are separate, the system is immune to ambient light sources. It is, however, important...