ensor design has changed over the years. From the early types which were often difficult to configure, to versions which are
now designed tomeet industry demands by being more complex with higher levels of performance and precision, but all the while being easier to use and set up. The intelligence of today’s sensors enable them to gather a larger amount of data, process it, and output a simple on/off signal or analogue value. However, although the built-in
intelligence means that most sensors will work to some degree in most applications, ensuring that they work reliably requires knowledge of each sensor’s strengths. The features of the most commonly used sensors tend to be known, but what about the more specialised products?
Ultrasonic sensors use a high frequency sound wave and time of flight to determine the distance fromthe sensor to the object. As the targetmust reflect the soundwave back to the sensor, a hard target will be better than a soft sound-absorbing target. As an example, a still liquid is a good target, whereas foamon top of a liquid isn’t.Wave
Ultrasonic sensors
guides or stilling tubes can, however, be used to eliminate the problem of foam on a liquid. The size and shape of the target also affects its performance.While a flat target perpendicular to the sensor is good, when the angle of the target varies fromperpendicular, the soundwave gets increasingly reflected away from the sensor,making a hard flat target at 30˚ fromperpendicular difficult to detect. Of benefit, ultrasonic sensors
tend to have a wide and long detection area – a typical sensor could detect a 500mmflat plate out to 8mdistance. At 4m distance the plate could still be detected if it were 500mm to the side of the centre line of the sensor, and a 25mm round rod could be detected 800mm from the centre line. These are also good for measuring distance,
especially if they incorporate temperature compensation, as the speed of sound changes with temperature. However, as the speed of sound also changes with pressure, avoid using ultrasonic sensors where the pressure changes. Ultrasonic waveguides often have a narrow slit in them to avoid pressure changes.
Safety Machine Analytics displays a live
visualisation of one or more machines so users can monitor the status of safety processes in real time, investigate the root-causes of stoppages, and take steps to eliminate them. The specially-developed SICK software supports improved Overall
Equipment Effectiveness (OEE) by acquiring data from safety sensors, then displaying interrupts in real time, as well as a graphical representation of system trends. Quickly and easily installed on any device with a web browser, the SICK Safety Machine
Analytics can be linked to multiple safety sensors or actuators, independent of hardware. Users get started by uploading images of their machines, then overlaying safety sensors onto the visualised scene to facilitate easy navigation of real-time data. With access rights set by the administrator, the system can then provide instant feedback, as well as longer-term historical analysis for maintenance and production management. Dr Martin Kidman, SICK UK machinery safety product manager, said: “SICK Safety Machine
Analytics is a simple and secure way of taking a virtual tour around the safety systems on your machines to look for any weak spots. You can drill down and identify any interrupts, so they can be quickly rectified. Once connected to a machine, this system offers a low-investment opportunity to identify where gains can be made in productivity by increasing machine uptime.”
12 Laser sensors An ultrasonic sensor relies on a moving
transducer to create and receive a sound wave in order to detect an object. Anything that can interfere with this transducer movement or the sound wave will affect the performance. For example, product labels, grease or a build-up of snow will interfere with the transducer movement; high winds and torrential rain can distort the sound wave.
Laser sensors use a single frequency and phase of light which creates a narrow intense beam of light that does not spread out and disperse as most light does. They are therefore ideal for detecting small objects at relatively large distances, or the absence of small features. These are capable of measuring tiny height
differences such as thousandths of a millimetre at short distances of a few hundred millimetres, or a difference of less than 10mm at a range of 250m. The small diameter, intense, light spot makes them easy to align and relatively immune to target colour. However, mirrored surfaces can be difficult to detect if they reflect the light away from the sensor, not back to it. To be eye safe, these have very little light
energy. This is concentrated in a very small area, so anything which disperses that energy will affect the performance, such as smoke, steam, rain or dirty lenses. As laser beams are so narrow, vibration can severely affect the sensor by moving the detection spot off of its target. At 1m range, a 0.5˚ angular vibration will move the spot 9mm.
Fibre optic sensors
Fibre-optic sensors are still the go-to option for very small spaces. Fibres can be routed into the heart of amachine with the sensormounted on the outside where it is easily accessible. Various
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