Getting down and dirty: Product research about discrete sensor trends
Control Engineering product research shows discrete sensors are getting smaller and easier to setup, and they can include short-circuit protection. Sensors need to detect transparent objects, differentiate between the object and background, detect flaws in microcomponents, automatically adjust to changing conditions. See charts.<br/>
Forget it. Gone are the days when sensors were asked to perform in neat, clean environments. Gone are the days when sensors could be large and bulky. And long gone are the days when engineers were satisfied with on/off contacts.
Now sensors need to detect transparent objects, differentiate between the object and background, detect flaws in microcomponents, automatically adjust to changing conditions, and must be able to do all this at a distance ranging from several millimeters to several feet. And size? No way, a sensor the size of a matchbook doesn't cut it anymore. It's gotta be smaller.
Control Engineering surveyed 1,500 readers to find what they expect from their sensors and how they're being used. Three-hundred sixty-eight responded for a response rate of 25%. Nearly all that responded, 95%, recommend, specify, and/or purchase discrete sensors (the basis for responses that follow). About two-thirds do it for in-plant requirements, and the remaining third do so for OEM (resale) requirements.
Where they're going
Despite their name, discrete sensors aren't solely for discrete applications. Many users are finding discrete sensors work well in continuous and batch processing applications. Eighteen percent of respondents use discrete sensors for continuous processing, 10% for batch processing, and 41% use them for both. Twenty-four percent use these sensors for discrete products manufacturing.
More specifically, respondants use the greatest number of discrete sensors, 69%, in machinery, followed by liquid fill-level (48%), raw materials processing (36%), solid and powder fill-level (29%), and packaging/palletizing. Results exceed 100% due to multiple responses.
Among types of sensors respondents use, photoelectric and inductive proximity sensors were tops, 74% and 73%, respectively. Capacitive proximity sensors came in third with 60%, while ultrasonic proximity sensors gathered 47%. Because respondents are apt to use more than one type of sensor within an application, results exceeded 100%.
Bob Fayfield, Banner Engineering (Minneapolis, Minn.) ceo, says inductive proximity sensors are still an industry favorite, and perhaps most end-users' first choice. He says they have practically no environmental limits and their sensing range doesn't require them to be excessively close to the object they're sensing. The drawback is they can only sense metallic objects
Photoelectrics are much better for sensing nonmetallic objects, Mr. Fayfield says. Photoelectrics can still sense metallic objects but the application must be suitable for an optical solution. Applications where the sensed object reflects light or has a shiny gloss aren't good for photoelectrics. Another drawback is they aren't practical in dirty, grimy environments, where airborne particulates can stick to the optics and throw off sensing accuracy.
Retroflective photoelectric sensors are the most used type of photoelectric, according to the survey. Seventy-eight percent of respondents use retroflective, with through-beam sensors not far behind at 68%. Limit-switch style photoelectrics garnered 56% of the tallies, while cylindrical and diffuse received 44% and 43%, respectively.
Expect diffuse sensors to start grabbing more market share, says David Lagerstrom, manager of industrial sensors and controls for Sick Inc. (Bloomington, Minn.). Now that advancements have improved background suppression, even when object and background are similar in color, diffuse sensors are gaining in accuracy. But, he says, since diffuse sensors are one of the 'more expensive sensors on the market, they must come down in price' to attract more buyers. Mr. Lagerstrom also says that diffuse sensors are still relatively new to the market. Once users become more familiar with the technology, he expects purchasing to increase.
What matters most
Once engineers decide on the type of sensor that best fits their applications, the features they most want in those sensors are alignment/set-up aid and short-circuit protection, followed by corrosion resistance, reverse-polarity protection, and intrinsic safety (see graph).
Cutler-Hammer sensors group (Everett, Wa.) product manager, Jeff Solberg, says his company works closely with customers to get a feel for what sensor functions they need. His customers also wanted features to help with alignment and set up, so the company developed a microprocessor-based control system called TargetLock. TargetLock allows additional optimization of alignment or range between target and sensor above what's necessary for the sensor to operate. TargetLock has a four-state LED indicator that warns users of gain reduction so they can maintain the sensor before it fails.
Most Banner Engineering sensors have a similar alignment feature called A.I.D (Alignment Indicating Device), which gives a signal proportional to the signal strength, 'much like a heartbeat,' says Mr. Fayfield. As the signal strength becomes weaker, so does the visual signal, telling the engineer to clean or realign the unit.
For the future, expect sensors to get even smarter. Many sensor companies are devoting much of their development time and money on embedded microprocessing. This isn't cutting edge anymore, it's more state-of-the-art, but it presents some exciting possibilities. At the very least, microprocessing is improving deficiencies in sensing methods. Capacitive and ultrasonic sensors have much to gain from microprocessing, since they're susceptible to moisture and noise respectively-microprocessing increases accuracy while limiting the effects of environmental interference.
The drive to make sensors smaller can also be attributed to microelectronics and microprocessing. The newest model of that cigarette lighter-sized photoelectric sensor you have has been reduced to the size of your thumbprint.
The sensors market looks stable for the next year. Nineteen percent of the respondents expect their sensor purchases to increase over the next year, while 52% expect purchases to remain about the same. Only 4% expect their companies to cut back on sensor purchases next year, while 19% are unsure and 6% had no answer.
Discrete Sensors Products
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Clear material sensing
Bloomington, Minn.- WL 12G photoelectric reflex sensor is said to be ultra sensitive for sensing glass/transparent objects or small parts. The sensor is equipped with automatic sensitivity adjustment to compensate for dust buildup. The diecast metal housing is designed to ensure accurate sensing and long sensor life. WL 12G has an operating range of six feet and can sense a range of clear material from plastic, to film, to glass. Though the WL 12G was designed for clear material sensing, it also can be used in many reflex applications.
Detect objects fast and small
Freeport, Ill.- LBS Series convergent beam laser photoelectric sensors provide background suppression capabilities and precise sensing zones, enabling the sensor to detect small objects and ingnore objects beyond the sensing beam's focal point. These sensors are designed for such applications as wafer mapping, printed circuit board detection, and integrated circuit inspection. Packaged in a zinc housing, the sensors are sealed to IP67. A selectable light or dark operate feature and separate power and ouptput indicators make setup easier. The sensors are powered by 12 to 30 V dc.
Honeywell Micro Switch
Three modes in one
Schaumburg, Ill.- E3X-DA digital fiber-optic amplifier displays digital incident, digital percentage, or analog levels. Users select the mode they would like to use with one touch of a button on the amplifier. Information is displayed in large 6 mm characters. This series of sensors is available in NPN or PNP versions, and users can choose whether or not they want analog output. To simplify setup and adjustment, users have a choice of four teaching methods, a hyperflashing function that sets the sensor's emitter to flash red for 10 minutes to ensure easy optical axis alignment; and a 'peak hold' or 'bottom hold' display that holds and displays a set value for 2 seconds. This display makes it easier to fine-tune optical axis adjustments or to detect objects moving at high speeds.
Targets are a lock
Everett, Wa.- SM Series photoelectric sensors use a microprocessor-controlled system called TargetLock to help users speed installation, improve sensor reliability, and eliminate unplanned downtime. TargetLock allows additional optimization of alignment or range between target and sensor above what is necessary for the sensor to operate. TargetLock features four-state LED indication proportional to the amount of sensing gain present. The LED will alert users of any gain reduction, so maintenance can be performed prior to sensor failure. The sensors also feature Perfect Prox background rejection sensing mode. High excess gain and a sharp optical cutoff are combined to allow detection of objects of any color or reflectance at the target range, while ignoring all background objects beyond that range.
Alternative to limit switches
Milwaukee, Wis.- VersaCube inductive proximity sensor is designed for applications where long sensing distance is a priority and space is a premium. It's also an alternative for applications that normally require a limit switch. VersaCube measures 40 x 40 mm and comes in a robust enclosure rated NEMA 6P, making it suitable for 1,200 psi washdowns. Installation can be done with a screwdriver. No special tools are needed. It also can be mounted five ways: from the top, front, back, left, and right positions.
Ontario, Calif.- Endevco's Model 256HX accelerometer is designed specifically for making shock and vibration measurements on small structures. It provides frequency response flat to 10 kHz and measures 0.55 in. high in a 0.44 in. hex. The device is based on an Endevco Piezite type P-8 crystal element, operating in annular shear mode. It uses a built-in, low-noise microelectronic amplifier to transmit low impedance voltage outputthrough the same two-wire cable that supplies constant current power.
Twinsburg, O.- F46 Series capacitive sensors have a slim, 5-mm profile, and can sense media through plastic or glass. The housing design offers two mounting options. The sensor can be mounted via standard cable ties to monitor flow in plastic tubing of various diameters. For level control of closely spaced vessels, this ultraslim sensor features two through holes for surface mounting. F46 sensors are available in general purpose and intrinsically safe (NAMUR) versions.
Pepperl + Fuchs
Ultrasonic sensor goes the distance
Minneapolis, Minn.- M18 ultrasonic sensors are for long-range sensing and can be used in environments where sensing may be difficult. They feature an 18 mm diameter barrel and a single transducer that functions as emitter and receiver. A single potentiometer sets the far limit of the M18's range. The fixed near limit, determined by the blind zone directly in front of the sensor, allows background suppression. The M18's large blind zone and narrow (6°) sonic cone are well-suited to detecting small objects in a limited area at long distances, and the sensors' synchronization and multiplexing features prevent mutual sonic cone interference so several can be used concurrently in the same area. Sonic impulses from up to six M18 sensors can be synchronized by tying their X1 lines.
Photoelectric is 1/3 previous size
Minneapolis, Minn.- Banner Engineering's Mini-Beam 2 sensors are one-third the size of their predecessors. The sensors feature a 12 mm threaded nose and advanced circuitry to streamline installation and set-up. All necessary adjustments are achieved using a single pushbutton. Combined with an advanced new algorithm, the sealed pushbutton digitally adjusts the sensor for optimal excess gain for all applications. Users hold the button to achieve maximum sensitivity (excess gain), then click the button for seven other settings. There's no need for screw potentiometers. Sensing modes available are regular and wide-angle diffuse (proximity mode), regular and polarized retroflective, convergent beam, and opposed (throughbeam). Sensing range is up to 4 m.