A photoelectric sensor is used to detect the presence (or absence) of an object, or for measuring the distance between a point and an object. It uses visible red light or infrared light from a transmitter and also has a photoelectric receiver. A photoelectric sensor becomes a popular choice in automation since they provide quick and reliable results without having to physically touch the object.
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Types of Photoelectric Sensors.
Photoelectric sensors come in different housing styles, sizes, and different working styles. There are three main types of photoelectric sensors:
1. Diffuse type photoelectric sensors
A light beam is transmitted in the direction of the object in question. The light is reflected from the object which is received by the receiver of the sensor confirming the presence of the object. The amount of light received is used by the sensor to measure the distance to the object.
2. Through-beam type photoelectric sensors
A light beam is transmitted from the transmitter on to a receiver while the object of interest is placed between the two. The object interrupts the light and changes the amount of light that falls on the receiver. This is used for sensing the object.
3. Retro-reflective type photoelectric sensors
A light beam from the transmitter falls on to a reflector. The reflector reflects back the light on to the receiver. The object of interest falls between the transmitter and the reflector and interrupts the light beam.
Depending on the requirement, the photoelectric sensor is selected. More sophisticated sensors that are aimed at higher accuracy come with the ability to suppress the background making it possible for them to precisely detect objects.
Applications of Photoelectric Sensors across various Industries.
Photoelectric sensors are widely used across many industries. Some of the industries are as listed below.
Food & Beverage Industry:
Manufacturing and packaging lines in the food and beverage industries also use photoelectric sensors. For example, a plant to cap bottles must be equipped with correctly aligning and orienting each bottle cap. If there are any mistakes in the positioning, the photoelectric sensors can help to detect them to allow for the smooth running of the plant.
Automotive Industry:
When the body of an automobile is built, each component needs to travel down the production line with reliable consistency. Each part needs to slow down and stop in front of the relevant station with perfect timing so that it can be welded or otherwise processed without any error. Photoelectric sensors can detect when the relevant station is near so that the line can stop and the component can be processed.
Photoelectric sensors used in the automotive industry have high precision that makes it possible for them to give accurate results even while operating around various objects with glossy surfaces.
Machine Engineering:
For big machines that need to be operated in perfect synchronization, photoelectric sensors can provide a good level of reliability. In such cases, there is no room for mistake and photoelectric sensors can help to make placement and removal of machine components efficiently.
Doors & Gates:
Automatic doors and gates, for example on buses, trains, elevators, garages, etc. need to have reliable sensing technology so that they open and close at correct times. The entire area in front of the door needs to be under the sensing area for the automated doors to work properly. Photoelectric sensors coupled with infrared scanners can detect approaching people or vehicles.
Material Handling:
In storage facilities that have complete or semi-automation, photoelectric sensors make it possible to efficiently track objects in storage, help with automating the storing and stacking of goods, and helps maintain inventories.
Pharmaceutical Industry:
Pharmaceutical industry applications such as packaging of medicines also use photoelectric sensors. During packaging, sensors can be used to avoid discrepancies such as empty packaging due to medicine tablets not being present on the line, etc.
Photoelectric sensors are evolving with the rise in demand and accurate, efficient sensors are available that can be used for various purposes. With a sensing range of up to 40mm, the Photoelectric Sensor range from Bulgin provides efficient sensing. They have a high IP rating making it ideal for them to be used in harsh conditions, too.
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Device used to determine location of an object
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Conceptual through-beam system to detect unauthorized access to a secure door. If the beam is interrupted, the detector triggers an alarm.
A photoelectric sensor is a device used to determine the distance, absence, or presence of an object by using a light transmitter, often infrared, and a photoelectric receiver. They are largely used in industrial manufacturing. There are three different useful types: opposed (through-beam), retro-reflective, and proximity-sensing (diffused).
Types
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A self-contained photoelectric sensor contains the optics, along with the electronics. It requires only a power source. The sensor performs its own modulation, demodulation, amplification, and output switching. Some self-contained sensors provide such options as built-in control timers or counters. Because of technological progress, self-contained photoelectric sensors have become increasingly smaller.
Remote photoelectric sensors used for remote sensing contain only the optical components of a sensor. The circuitry for power input, amplification, and output switching is located elsewhere, typically in a control panel. This allows the sensor, itself, to be very small. Also, the controls for the sensor are more accessible, since they may be bigger.
When space is restricted or the environment too hostile even for remote sensors, fibre optics may be used. Fibre optics are passive mechanical sensing components. They may be used with either remote or self-contained sensors. They have no electrical circuitry and no moving parts, and can safely pipe light into and out of hostile environments.[1]
Sensing modes
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A through-beam arrangement consists of a receiver located within the line-of-sight of the transmitter. In this mode, an object is detected when the light beam is blocked from getting to the receiver from the transmitter.
A retroreflective arrangement places the transmitter and receiver at the same location and uses a reflector to bounce the inverted light beam back from the transmitter to the receiver. An object is sensed when the beam is interrupted and fails to reach the receiver.
A proximity-sensing (diffused) arrangement is one in which the transmitted radiation must reflect off the object in order to reach the receiver. In this mode, an object is detected when the receiver sees the transmitted source rather than when it fails to see it. As in retro-reflective sensors, diffuse sensor emitters and receivers are located in the same housing. But the target acts as the reflector so that detection of light is reflected off the disturbance object. The emitter sends out a beam of light (most often a pulsed infrared, visible red, or laser) that diffuses in all directions, filling a detection area. The target then enters the area and deflects part of the beam back to the receiver. Detection occurs and output is turned on or off when sufficient light falls on the receiver.
Some photo-eyes have two different operational types, light operate and dark operate. The light operates photo eyes become operational when the receiver "receives" the transmitter signal. Dark operate photo eyes become operational when the receiver "does not receive" the transmitter signal.
The detecting range of a photoelectric sensor is its "field of view", or the maximum distance from which the sensor can retrieve information, minus the minimum distance. A minimum detectable object is the smallest object the sensor can detect. More accurate sensors can often have minimum detectable objects of minuscule size.
Certain types of smoke detector use a photoelectric sensor to warn of smouldering fires.
Difference between modes
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Name
Advantages
Disadvantages
Through-beam
- Most accurate
- Longest sensing range
- Very reliable
- Must install at two points on system: emitter and receiver
- May not detect translucent objects
- False triggers when misaligned.
Reflective
- Only slightly less accurate than through-beam
- Sensing range better than diffuse
- Very reliable
- Must install at two points on the system: sensor and reflector
- Slightly more costly than diffuse
- Sensing range less than through-beam
- May not detect objects with high albedo
LASER-Reflective
- Single point installation
- Good for detecting small objects
- Clearly defined sensing ranges
- Very reliable
- Blind to objects outside specified range
- Not good for mirror finishes
Diffuse
- Only install at one point
- Cost less than through-beam or reflective
- Less accurate than through-beam or reflective
- More setup time involved
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See also
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References
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