Optical sensors have background and foreground suppression

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The new Bulletin 44B photoelectric sensor from Rockwell Automation, which is equipped with adjustable background and foreground suppression, provides an effective solution to the common problem of how to ensure accurate recognition of objects - especially where the target is close to a surface that must be ignored, such as a conveyor.

The Bulletin 44B sensor incorporates a dual-receiver optical system, which - unlike standard diffuse-type sensors - allows it to actively 'see' both the target and background areas, while suppressing any background reflections. The result is claimed to be more reliable object recognition and fewer false alarms that might otherwise cause unnecessary product rejection or loss of production.

Customers can choose to use either background suppression or foreground suppression mode, both of which utilise a cost-effective, common optics system designed to reduce false triggers due to background reflections. Both sense modes recognise the background condition using a second internal receiver; the behaviour of the sensor depends on whether it is operating in background or foreground mode.

In background suppression mode, the Bulletin 44B changes its output state when it 'sees' reflected light from the target; in foreground suppression mode, it uses the background as a reflector and changes its output state when a target blocks this reflector. The background suppression sense mode is best suited for the detection of light targets against a less reflective background. For example, in the detection of missing bottle caps, the sensor 'sees' the bottle cap by the reflected light from the cap, while ignoring the bottle itself.

Foreground suppression is more effective when detecting a dark or irregularly shaped target against a highly reflective background. This mode is useful for the detection of products on a reflective white conveyor belt. The sensor 'sees' the product by the absence of reflected light from the belt.

The Bulletin 44B is designed to be robust enough for most industrial applications: the rugged IP67-rated 'square-style' housing provides a high degree of environmental protection, allowing it to be used in water washdown environments. LEDs give a visual indication of power, output and stability status and electrical connection is via a M12 QD connector, designed to help prevent wiring errors. Versatility is further enhanced by dual NPN and PNP outputs and the 90-degree swivel design allows the 44B to be mounted in a wide variety of positions. Sensing range is 300mm and the response time is 1ms.

With its innovative optical design, dual-mode suppression and fast 1ms response time, the Bulletin 44B provides a highly effective yet versatile optical sensing system, helping to ensure high-quality production line output with the minimum of false triggers.

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