When to Use Banner Photoelectric Sensor？

In opposed-mode sensing, the sensor's emitter and receiver are housed in two separate units. The emitter is placed opposite the receiver, so that the light beam goes directly from the emitter to the receiver. An object is detected when it "breaks" or interrupts the working part of the light beam, known as the effective beam. Depending on the application, opposed mode sensing provides the highest reliability whenever it can be implemented. This is because light passes directly from the emitter to the receiver. Then, when an object breaks the beam, the output will switch.

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• Opposed-mode sensing offers the highest level of excess gain (sensing energy)
• Long sensing range
• Most robust for harsh environments
• Precise position sensing
• Small-part detection using lens apertures
• Impervious to surface reflectivity (the color or finish of the object)

A retroreflective sensor contains both the emitter and receiver elements in the same housing. It uses a reflector to bounce the emitted light back to the receiver. Similar to an opposed-mode sensor, it senses objects when they interrupt or "break" the effective beam. Because retroreflective sensing is a beam-break mode, it is generally not dependent upon the reflectivity of the object to be detected. 

However, it can be tricked by shiny objects. For those targets, a polarized retroreflective sensor should be used to prevent proxing. Proxing is when an object with a shiny surface returns enough light to the sensor to mimic the photoelectric beam coming back from the reflector and causes the object to not be detected. In a polarized retroreflective sensor, the emitter sends light waves through a filter that aligns them on the same plane. These light waves bounce off the reflector, and return to a vertically polarized filter on the receiver. When this polarized light reaches a shiny target, the light is reflected back to the sensor on the same plane as it was emitted and is blocked by the filter, signaling a broken beam. When the polarized light hits the reflector, however, it is scattered into unpolarized light with light waves on both the horizontal and vertical planes. Some of this light will pass through the receiver’s filter and the sensor will detect the reflector and know the beam is unbroken. 

A retroreflective-mode sensor offers a convenient alternative to opposed mode when space is limited, or if electrical connections are only possible one side of the installation. Retroreflective-mode sensors offer relatively long ranges. 

• Second-highest excess gain mode 
• Polarized model available to prevent the beam from proxing off shiny objects 
• Coaxial optics available for clear objects and precision 

Diffuse-mode sensors contain the emitter and receiver in the same housing but do not use a reflector. Instead, they detect an object when emitted light is reflected off a target and back to the sensor. With a diffuse-mode sensor, the object is detected when it "makes" the beam; that is, the object reflects the transmitted light energy back to the sensor. They are significantly affected by the reflectivity of the target objects, which can drastically shorten their range. These sensors should not be used in applications with very small parts that need to be detected, in parts-counting applications, or where a reflective background is close to the object to be sensed. Diffuse-mode sensors are very convenient and are often used when opposed or retroreflective-mode sensors aren't practical.

• Low installation effort
• Does not require a reflector

Excess gain is a measurement of the amount of light energy that the receiver element detects. A sensor needs an excess gain of one to cause the sensor's output to switch "on" or "off." However, contaminants in the sensing environment such as dirt, dust, smoke, and moisture can cause signal attenuation, so more excess gain will be required to receive a valid signal. Excess gain may be seen as the extra sensing energy available to overcome that attenuation.

An excess gain chart shows how much light energy is available at a given distance. The dirtier the environment, the more excess gain will be needed to overcome it. The graphs are logarithmic, which allows for a concise overview of data that varies by several orders of magnitude. Each minor tick increases by a factor of 1, and each major tick increases by a factor of 10. For example, starting at the origin and moving up the Y-axis, the graph's ticks represent 1, 2, 3, etc. Once the tick gets to 10, the ticks represent 10, 20, 30, etc. When the tick gets to 100, then the ticks represent 100, 200, 300, and so on.

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We are often asked whether or not a particular sensor such as the DX80N9Q45LP from Banner Engineering Corporation need a reflector to operate.

Photoelectric sensors use light to detect the presence or absence of an object within the sensor’s field of view. Whether or not your sensor needs a reflector to operate depends on which type of sensor you are looking at purchasing.

There are three main types of photoelectric sensors:

Through-Beam Sensors: Through-beam sensors use a separate emitter and receiver. The emitter releases a beam of light that travels straight to the receiver, typically creating a normally closed circuit. If the beam of light is blocked by an object the circuit switches to an open circuit. The through-beam sensors can detect objects over long distances but require careful placement and alignment to ensure proper operation. Clear objects may not be detected by this type of sensor.

Retroreflective Sensors: Similar to the through-beam sensors these sensors use an emitter and a receiver to send and detect a beam of light, however both the emitter and receiver are contained within the same unit. For proper detection of objects retroreflective sensors require a reflector be mounted directly across from the sensor. Like through-beam sensors these are typically normally closed circuits and switch to normally open circuits when an object is detected. Retroreflective sensors have a shorter range than through-beam sensors and may not detect shiny objects because they reflect the light back similar to the way the reflector does.

Diffused Sensors: Similar to retroreflective sensors the emitter and receiver in a diffused sensor are housed within the same unit. However, rather than relying on a reflector to bounce the light back to the sensor it instead uses the object itself. Their circuit typically behaves the same as the other two types of sensors. Because it uses the object to return the light, diffused sensors have the shortest range of the three and may not detect objects with less reflective surfaces.

So, back to our question above. We now know that because the DX80N9Q45LP is a retroreflective sensor it does require a reflector for proper operation.

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