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Compare photo sensor to ultrasonic sensor for product detector in a packing line, in teams of accuracy

FELIX EFOSA Ogieriakhi

 Technical Observation and Suggestion on Product Detection Sensors

During my role as an Electrical Maintenance Engineer in a bottling company, I worked directly with photoelectric sensors for product detection on the final packaging conveyor line. These systems, typically comprising an emitter and a crystal reflector, functioned effectively at first. However, over time, issues such as product detection failures, sensor misalignment, and reflector contamination became common, impacting both production accuracy and maintenance load. At the time, photoelectric sensors were the only detection technology I had hands-on experience with. However, during my master's degree studies, I gained further exposure to advanced sensing technologies, including ultrasonic sensors and I came to understand their significant advantages in industrial automation. Ultrasonic sensors operate using sound wave reflection rather than light, making them far less susceptible to interference from transparent packaging, shiny surfaces, or dust and moisture all common in bottling environments. Recommendation: If advising any production facility facing similar detection issues with photoelectric sensors, I would strongly recommend evaluating ultrasonic sensors as an alternative. Despite a slightly more involved installation process, they offer: Superior reliability in harsh or variable conditions Consistent detection across a wide range of product shapes and materials Reduced maintenance requirements Improved long-term accuracy and process stability A trial installation on a single conveyor section could serve as a valuable proof of concept before full-scale deployment. 

  • Hello Felix:

    Ultrasonic senors are used in medical testing for viewing beating hearts and unborn babies.

    However they must be in direct contact with the outside of the skin and coupled with some sort of cream.

    What is the maximum size of the air gap between a bottle shaped object and the sensor?

    Peter Brooks 

    Palm Bay FL

  • in reply to Peter Brooks

    Through air ultrasonics are certainly possible - I recall early TV remotes used ultrasonic rather than infrared as a transmission medium (worked over several metres) and i think some robotic collision avoidance systems use ultrasonics too (e.g. https://thepihut.com/products/ultrasonic-distance-sensor-hcsr04). The medical scan systems are probably much more challenging as they're trying to create a complex image rather than just a there/not-there signal.

       - Andy.

  • in reply to AJJewsbury

    one can make 'broken beam' air-path ultrasonic sensors, but like the optical, they come with problems - light is good at edge detection, sound waves of wavelength centimetres are not so good - great for a reversing sensor on a car when reversing into a wall, as it will detect over a large cone, but not good for a thin object like a lamp post, which  may be missed as reflections are all over the place, & diffraction causes the wave to re-form beyond it.

    Acoustic interference from machinery - a lot of motor controllers 'squeal' in the ultrasonic and the problems of reflections of your sound giving multipath responses, also need to be considered.

    You know the issues with optics ;-)
    Consider sensing with multiple wavelengths, as the optical performance of coloured or transparent objects are often very different in the infra-red. It always tickles me that red wine becomes almost clear at 850nm , a common TV remote control frequency.



    Mike.

  • in reply to mapj1

    Hello Mike:

    I believe another factor relating to measurement accuracy, is the humidity of the air.

    Peter Brooks

  • in reply to Peter Brooks

    yes over long distances, certainly for ultrasonic 'radar' and ranging  as moisture changes the sound velocity, and attenuation, but probably not hugely significantly  over indoor sort of distances. The other problem for sound generally especially in places open to the outdoors is that a draught affects the effective speed of sound as unlike light,  there is a medium whose velocity adds or subtracts to or from the much as water flow alters the speed of a boat.

    Equally in systems that are outdoors by design, it is entirely possible to measure and compensate for this - the obvious application is gun-sound rangjng using field arrays of microphones and collecting phase delay information. Modern systems are pretty much self calibrating.

    Mike

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