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FEATURE SENSORS & SENSING SYSTEMS MOBILE EQUIPMENT: SEN


The sensors and control sy mobile equipment often ne extremes of temperature


Used across the


world in a range of applications, the


sensors and controls on mobile equipment need to withstand a wide variety of demands and environmental


conditions. Here, Turck Banner takes a look at the challenges faced


lift, AGV, crane, automatic car wash or combine harvester, and even down to smaller items like generators, these are used across the world in a variety of environments and have to face a diverse range of environmental conditions. So when you consider the applications they


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are used for, the sensors and control systems used on mobile equipment therefore often need to withstand extremes of temperature, exposure to rain and sunlight, humidity, dirt, dust and much more. As each application will require a different


combination of properties, companies like Turck and Banner need to combine these properties into as few sensor or control variants as possible – but without forcing the cost up.


WITHSTANDING APPLICATION DEMANDS


While industry standards are of course in place, these can’t always be relied on to ensure a part is going to survive for an extended period of time. Take IP67 and IP69K as an example. While these will prevent water ingress under test conditions, air inside a part that is exposed to sunlight and rain will expand and contract, drawing moisture through seals and damaging the part. However, fully potted parts with welded seams will not suffer from his problem. Another problem is


temperature. Mobile equipment is used across the world,


20 DESIGN SOLUTIONS MAY 2024


obile equipment could be described as anything that moves around on wheels. Ranging from such machinery as a fork


potentially in areas where the sensors and control systems have to operate at temperatures as low as -40˚C, however the working temperature for many products is -10 to +70˚C. To meet application demands, low temperature sensors and controls have therefore been developed, as well as high temperature products with operating temperatures of 85, 100, 200, 250 and 480˚C. Another issue is temperature stability. Normal


temperature fluctuations encountered inside a factory have little effect on the measuring accuracy of most sensors, whereas sensors without temperature compensation become very unreliable outdoors as a result of direct sunlight and shade, the direction in which the machine is travelling, plus wind, rain and snow. These factors can make all but the best temperature compensated sensors unusable. Finally, the operating DC voltage range is


also a consideration, as mobile equipment will often experience a greater voltage fluctuation than other equipment. Sensors and control systems for mobile equipment must be able to tolerate voltage spikes and dips created by other devices switching on and off. So let’s now take a look at the sensor types.


OPTICAL SENSORS A clean optical sensor will work well at its stated maximum range until it starts to get dirty, or it begins to rain or snow. In addition, direct sunlight can temporarily blind an optical sensor. High powered optical sensors used at their optimal range can cope with higher levels of dirt; and introducing a slight downwards tilt to the sensor mounting can help considerably with sunlight saturation. Sunlight immune optical sensors are available, and other sensing methods are unaffected by sunlight and dirt. As an example, inductive sensors are


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