Feature Sensors & sensing systems M


odern manufacturing facilities, warehousing and process envi- ronments rely on sensors and sensing systems for everything from quality control and presence detection to ensuring operator safety. Selecting the right sensor can have a significant impact on a business, enabling immediate benefits in terms of quality improvement, energy savings and manufacturing speed and volume. It is surprising how many manufac- turers vocalise concerns about existing


in use, must be able to eliminate errors and false operation caused by radio frequency emissions. High frequency lighting and even flashing beacons on forklift trucks can also cause spurious triggering of optical sensors. Sensors used in cold store environ- ments can be exposed to temperatures as low as -40oC. If located near a door, where the temperature is likely to rise periodically, condensation may occur on the lens. The lens could also freeze and ice over when the temperature


Pin-point LED technology delivers performance comparable to a short range laser scanner


Taking the confusion out of sensor selection


As the range and capabilities of industrial sensors expands to meet the growing needs of industry, selecting the right one for the individual project requirements becomes increasingly important. Specifying the right sensor can, however, be a confusing process. Phil Dyas, sensor specialist at SICK (UK), examines some of the key factors to consider


sensors on, for example, production or packaging lines, only to find that the machine design has actually been modified to suit the sensor limitations. The range of sensing systems on the market is vast. Combined with the sensor manufacturers’ ability to modify a sensor to meet the exact application needs, this means the sensor can, and should be, specified to meet individual project requirements rather than the other way around.


Off the shelf solutions may, of course, suit exactly, and being able to call on the resources of an advanced and comprehensive product range is advantageous. But very often simple modifications can achieve a best prac- tice solution at little or even no cost. If you consider that sensors can control critical points of production, and that a less than satisfactory sensing solution can allow faulty products through, cause line outages, and affect timing and phasing, you can see that unsuitable sensors can cause poor margins. In these credit squeezed times, product and energy wastage is unforgivable. Knowing the environ- ment that the sensor will operate in and how this could affect the operation of the sensing system is key to ensur- ing optimal performance.


Considering the environment The environmental conditions of each production facility – where there may be exposure to high frequency lighting or EMC, etc., – can have a significant impact on the type of sensor specified. It is therefore important to examine how these environmental factors might affect the performance of certain types. For example, sensors deployed on a logistics site, where mobile phones or two way radios are


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drops again. To counteract this, sensors with heated lenses and heated reflec- tors should be considered. The type of cabling must also be considered: PVC cabling is commonly used on sensors, however this is not suitable for extreme cold as PVC turns brittle at low temperature.


Specifying sensors for high tempera- ture environments, such as the steel and glass industry, also poses a number of issues. Most sensors have an operating temperature limit of 70oC, which is far exceeded in such environments. Specifying a sensor with cooling plates and high temperature reflectors can extend the operating envelope to around 100oC. A metal housing and glass lenses as opposed to plastic will also combat any issues with melting. In environments where conveyor belts are in operation, excessive vibra- tion can cause a sensor to misalign; and where forklifts are used the likelihood of knocking a sensor is increased. Specification for such environments should include a high-strength, wrap around bracket which offers protection against physical damage and also pro- tects the electrical supply connection.


A fit for purpose product Selecting a photoelectric sensor with the correct optical method is crucial for achieving reliable and consistent prod- uct detection quality. It is important to understand the varying characteristics of beam geometry between direct diffuse and retro-reflective or through beam detection methods to ensure the most efficient machine design. Manufacturers often choose a diffuse detect sensor as it has an easier mount- ing configuration, but if this is not right for the application the sensor will under- perform and quality issues can arise. Pin-Point LED technology, which delivers performance comparable to a short-range laser scanner, with the ability to detect objects down to 1mm and distances up to 500mm, is becom- ing increasingly popular. Pin-Point technology doesn’t need the safety regime required for lasers, has a wider temperature operating range and, at 100,000 hours, typically lasts twice as long as a laser diode device.


Sensors specified with cooling plates can operate in high temperature environments up to 100˚C


Move outside the comfort zone Given the variety and complexity of sensors available today, it is not uncommon for engineers and manufac- turers to simply specify sensors within their ‘comfort zone’ rather than those that are right for the job. However, selecting a sensor which is not fit for purpose will have a significant impact on productivity, quality, maintenance and inventory, as well as cost. An in-depth under- standing of the range of sensors avail- able, and the impact of operational conditions, is therefore essential when specifying sensors.


SICK (UK) T: 01727 831121 www.sick.com/uk


Enter 216 MARCH 2011 Design Solutions


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