Embedded intelligence increases photoelectric sensor reliability
New IP69K-Rated Sick W12-3 photoelectric sensor with rotating connection withstands washdown environments; Sick OES3 ASIC, provides smart background and foreground suppression.
Sick W12-3 photoelectric sensor uses Sick's third generation application-specific integrated circuit (ASIC), the OES3. The new ASIC delivers what Eric Simmons, Sick product specialist, describes as "best-in-class background and foreground suppression." He says the OES3 was developed through years of research to determine the best ways to detect an object at its true location while maintaining a good black / white shift and the ability to ignore possible interference, such as high frequency lights, another sensors light source, false outputs caused by reflections from shiny targets beyond the sensors sensing range.
The Sick OES3 ASIC addresses background and foreground suppression, Simmons says, in the following ways.
- Black/white shift: Black absorbs much more light than a white target, Sick uses the Kodak color scheme white = 90% reflectivity and black = 6% reflectivity.
When a target changes color (either on the same package or after a recipe change) sensors may not be able to detect the differing colored targets. This would cause the sensor's output to turn off and then back on which must be handled by software or the sensor needs to be readjusted. W12-3 with OES3 technology can detect the multicolored object without the sensor's output turning off and on or having to readjust the sensor when products change color.
- Stray reflections: Sick sensors using the OES3 chip can to ignore stray reflections beyond its sensing range that may reflect back and flood its receiving elements. This could be caused by someone walking past with a reflective vest, a window being opened beyond the sensors sensing range, a shiny object moving beyond the set point, and similar environmental challenges.
Sick W12-3 photoelectric sensor
- High frequency lighting: Energy efficient, high-frequency (HF) fluorescent lighting can wreak havoc on photoelectric sensors. Embedded intelligence recognizes when a HF light is present and will not "chatter."
- Another sensor's light source: Cross talking occurs when two sensors are pointed at one another. Sensors are modulated to a unique frequency but may have instances when they are nearly in phase or a pulse is in the same modulation as its own light source, because of this similar phase the sensor thinks that it is seeing a target within its sensing range.
These sensors can recognize when another sensor's light source is nearly the same modulation and adjust.
How the ASIC design helps
Four key features in the OES3 chip, Simmons says, meet customer needs:
- 16 element logarithmic array: The OES3 sensor uses a 16 element logarithmic receiver array that is segmented from bigger to smaller sizes. This logarithmic design will allow high-performance background suppression at an extended range, as a target is moved farther away from the sensor the light returning to the receiver gets smaller. With normal receiver elements, the sensor has trouble distinguishing between background and target.
- Active area management: The OES3 chip has a second sender LED, called the Pilot LED, that sends out light offset from the main sender LED by 4 micro seconds. The Pilot LED is a diffused light that is designed to detect any potential false reflections caused by a shiny/glossy targets outside the set sensing range. Reflections returned from the Pilot LED are recorded by the OES3 ASIC, and if the stray reflection is returned from the main sender in the same location and intensity as the Pilot LED the sensor's output will not become active. False trips caused by stray reflections (such as reflective vests, windows, shiny / glossy backgrounds) is virtually eliminated because of the active area management feature.
- Self adjusting light spot: It has the ability to adjust the light spot based on the reflectivity of the target it is detecting. If the target presented to the sensor is highly reflective and the receiver elements become flooded with light the sensor will tune down the intensity of the sender LED to compensate for the amount of light being received so that the true location of the object can be detected. If the target presented to the sensor is very dark, the sensor will tune up its intensity so that enough light is being received by the receiver elements to detect the object's actual location.
- Passive area management: The sensor can ignore high frequency lighting and one other sensors light source. It does this by checking the area for the HF lamp when it is not looking for its own modulated light source. When the sensor does look for its own light, because of modulation, it will know that there is a HF light causing interference and will filter out the noise caused by the HF light.
Read a Control Engineering discrete sensing feature article on proximity, inductive, laser sensors, " Proximity Sensors: How to Choose, Use Them ."
- Edited by Mark T. Hoske, editor in chief, Control Engineering www.controleng.com
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