Presence Detection Crosses Industry Borders

Advances in sensor technology have been a driving force in factory automation, most would agree. Interfacing the real world and analog/digital input to control processes has never been more applicable to a wider range of automation functions than it is today. Automating discrete manufacturing applications has, arguably, lagged behind process industries.


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Advances in sensor technology have been a driving force in factory automation, most would agree. Interfacing the real world and analog/digital input to control processes has never been more applicable to a wider range of automation functions than it is today. Automating discrete manufacturing applications has, arguably, lagged behind process industries. Improvements in discrete sensing, particularly in proximity senor technology, have expanded automation in these industries.

According to a recent online survey of control engineers conducted by Control Engineering magazine and the Reed Research Group, proximity sensors have found their way into a wide variety of automated industries. When asked about the primary application for proximity switches in their operations, 36% of those responding cited both continuous and batch processing. Discrete manufacturing accounted for 29% of the applications, continuous processing only accounted for 16.7%, and utilities for 7.2%. Batch processing only claimed 4.3% of respondents. Other operations came in at 6.5%.

Applications abound

Applications for proximity sensors are long and varied. Most common, regardless of industry type, were machinery applications. They accounted for 79.7% of the total, more than twice that of liquid fill-level (32.6%), packaging/palletizing (31.2%), solids/powders fill-level (26.1%), and raw materials processing (20.3%). Other applications included fabricated metal (17.4%), plastic products manufacturing (14.5%), automotive (10.1%), and web-based products (4.3%).

Machine Control & Discrete Sensors

Among changes from the 2002 survey on proximity sensors, 2005 results show significant gains in the other category, which indicate other bus technologies entering the arena.

When asked about the mix of applications, Ernie Maddox, product manger, position sensors at ifm efector inc. ( ), says he believes them to be accurate. 'Applications for proximity sensors in continuous or batch processes are limited. In discrete manufacturing, proximity sensors are used for both detecting machine position and detecting products being manufactured. Use of proximity sensors for detecting machine position has grown dramatically over the past 15 years. The primary reason for this trend has been the switch from mechanical switches and relay logic to the use proximity sensors and PLCs by machine builders. This trend has now run its course for the most part.'

In the product detection arena, applications include part presence in fixtures, part counting on conveyors, and 'line full/line empty' detection on conveyor lines and machine infeeds. According to Maddox, the trend is growing 'as manufacturers continue to implement sensors to improve production rates and to improve the quality of parts being manufactured. Error proofing and part verification are major trends today.'

Rough, tough, rugged

Corrosive environments, moisture, and collisions (and even near misses) with sharp, heavy, oily, or abrasive parts can be rough on proximity devices. Serdar Guvenc, product manager at Sick Inc. ( ) points to ruggedness as an essential design characteristic that is growing even more significant. 'Sick sees both price and ruggedness as very important,' says Guvenc. 'While standard inductive sensor pricing is declining due to standardized manufacturing techniques,' he continues, 'many manufacturers in the food and beverage and pharmaceutical industries are willing to pay a premium for proximity sensors that can withstand their application environment and eliminate the need for replacement (and associated downtime) during a production run.'

Machine Control & Discrete Sensors

New proximity sensor characteristics rated important by respondents were automatic sensitivity adjustment and self-teach feature, ranking fourth and seventh, respectively.

Longer sensing ranges, more resilient construction materials and techniques, and better electronics/cabling have all added to the ruggedness of proximity sensors overall. However, these features are often available only in premium units at prices higher than standard. In each case, users need to weigh installed cost against production downtime.

Sensors unplugged

Most users still do not use sensors on a device network. Those who do, however, use standard sensors with interface modules more than twice as often as network-enabled varieties. According to Nazario Biala, proximity sensor product manager at Omron Electronics LLC ( ), this trend will continue, at least in the short term.

'A couple of things need to take place before the 2:1 ratio can change,' says Biala. 'First, users of industrial automation need to be better educated on the benefits of system and device-level networks. Associations, such as ODVA [Open DeviceNet Vendor Association; ], have done a good job of educating the industry of the benefits of implementing device-level networks. However,' he goes on, 'a wider scope of industry education needs to take place for wider market acceptance. Additionally, the industry is waiting for the cost of network components, such as photoelectric sensors and proximity sensors, to come down,' Baila says, adding that those waiting for a winner in the fieldbus wars have been missing benefits of network-enabled devices.

Looking at communication technologies preferred by those who use networked sensors in automation systems revealed interesting changes from the previous survey (see accompanying graph on communication protocols). Although the lineup stayed essentially the same over the three-year time period, there were significant gains in the other category. Mentioned most often is Modbus Plus.

Why buy?

No matter which technology fits the application, those who buy proximity sensors provided a litany of reasons for specifying them (see accompanying graph on buying characteristics). Characteristics termed important remained essentially the same from survey to survey, except for automatic sensitivity adjustment and self-teach feature which appeared for the first time in 2005. In the current report, the self-teach feature ranked fourth while automatic sensitivity adjustment came in seventh.

As with most technologies, new features almost always increase adaptability to the industries the devices target. Proximity sensors are no exception. Today's electronic capabilities have made set-up and, in some cases, flexibility of these devices much easier for those who specify and apply them. As the devices become more sophisticated and adaptable, control engineers will find more places to use them.

Proximity sensor products

For more manufacturers, visit . For more information on the products described here, visit the Web sites listed.

Small-package proximity sensors

Machine Control & Discrete Sensors

Line of proximity sensors includes inductive, capacitive, ultrasonic, and analog output types in a variety of sizes and with short-circuit protection. Standard and double/triple sensing distances vary by model. Small-package sensors are suited for applications with limited mount space. Ultrasonic 18- and 30-mm products are high resolution with dc or analog output. All ultrasonic dc models have an LED indicator and can be purchased with adjustable sensitivity. Four models in the analog series feature voltage or current output, metal housing, and axial or quick-disconnects. AutomationDirect

Ultra-miniature photoelectrics

Machine Control & Discrete Sensors

Q12 Series of ultra-miniature photoelectric sensors is the smallest model in the World-beam family, roughly the same thickness as a U.S. quarter and only 8-mm wide. Self-contained devices have an over-molded design to achieve an IP67 environmental protection rating for harsh industrial environments. Available in opposed, retro-reflective, polarized retro-reflective, and fixed-field modes, devices have sensing ranges up to 2 m. Robust, metal-sleeved side-mounting holes simplify installation in confined locations. Applications include materials handling, packaging, semiconductor, pharmaceutical. Banner Engineering

Sensors for metal detection

Machine Control & Discrete Sensors

Uprox + sensors precisely detect such materials as iron steel, stainless steel, copper, aluminum, and brass at increased distances with no reduction in rated sensing. Multicoil system replaces the wound coil in conventional ferrite core inductive sensors to achieve sensing distances up to 250% greater. Housing designs vary. Integrated predamping protection reduces the metal-free mounting area and allows traditionally flush-mounted sensors to be recessed by half a turn for increased mechanical protection. All adhere to present EN50082-2 standards. Turck

Extended-range sensors

Machine Control & Discrete Sensors

E2A line of modular extended range proximity sensors offers 1.5 to 2.0 times the sensing distance of standard sensing range proximity sensors. Extended range lets users mount devices farther from tooling and work pieces, eliminating collisions and sensor damage. Line includes more than 220 models. Sensors come in M8, M12, M18, and M30 sizes in shielded or unshielded construction, NPN or PNP output, a range of barrel sizes and materials, and a choice of wiring options. Sensing distances range from 2-30 mm. Thick housing minimizes damage from over-torquing; fully vacuum-potted construction eliminates air pockets that can cause thermal, moisture, or vibration failure. Built-in wrench flats and LED operation indicators ease installation and maintenance. Omron Electronics LLC

Miniature sensors

Machine Control & Discrete Sensors

Miniature magnetic cylinder sensors incorporate giant magnetoresistive (GMR) technology to provide extremely high sensitivity to magnetic fields in pneumatic cylinder applications. DC devices fit C-slot and T-slot cylinders, come in a variety of cabled and pigtail models, and offer top-loading mounting that eliminates the need to remove cylinder end caps. Integrated friction tab prevents sensor from sliding, even in vertically positioned cylinders. GMR technology is said to give sensors high accuracy, fast response times, and immunity from long-term effects of magnetic fields. They are polarity independent and provide reliable piston-position detection regardless of magnet orientation. w.ifmefector.comifm efector

Rugged, inductive sensors

Machine Control & Discrete Sensors

Pile Driver family of inductive sensors is fully flush mountable and said to be the most compact, all-metal devices available. Rugged 8-mm dia units are tested to provide a life span 20 times that of conventional plastic-faced sensors. They come standard with 100% stainless steel housings and are available with weld-spatter resistant coating and a variety of cable options for long life in harsh environments. Repeatability is better than 0.01 mm, hysteresis is 5%, and operating temperatures range from -14 to 158 8C. Sensors are intended for harsh, space-restricted applications with such hazards as lubricants, cutting fluids, metal shards, and target impacts. Pepperl+Fuchs

Small-diameter sensors

Machine Control & Discrete Sensors

Inductive sensor combo with, says the manufacturer, the world's smallest diameter—3 mm—comes in shielded and unshielded versions. Sensors use an integrated flush fitting in place of a standard connector, making each package 3-mm wide for the entire length of the device. Unshielded version has a 3-mm ferrous metal sensing distance; shielded version has a 1-mm distance. Applications include embedded installations, such as in stamping dies; tight, difficult to install situations; and places where devices need to be as close as 6 mm to one other. Balluff

Distance measurement devices

Machine Control & Discrete Sensors

DT 60, DL 60, DT 500, and DS 500 distance measurement sensors augment the company's existing line. Low-cost alternative is said to handle a variety of material handling, logistics, and general manufacturing applications, including dimensioning on a conveyor, continuous detection of the diameter of paper or steel coils, automating small parts detection in a warehouse, and anti-collision control for high-speed gantries or cranes. All feature quick setup time and high accuracy and repeatability. Sick Inc.

Programmable outputs

Machine Control & Discrete Sensors

IWRM 12Z8704/S14C analog inductive proximity sensor features independently programmable digital and analog outputs. Self-contained unit delivers highly precise non-contact proximity, position, and distance sensing for metal objects and can identify two metal substrates in the same application. Sensor features digital output with two selectable trigger points and may be used for sorting metal objects, concentricity or shape sensing, assessing wear measurement and circularity, and thickness measurement. IP67- approved device has an operating range of 0-4 mm, and a resolution of 0.005 mm with a deviation of 0.05 V for consistent output. Baumer Electric

Inductive sensor has multiple features

Machine Control & Discrete Sensors

iProx programmable inductive proximity sensor includes a programmable sensing range, built-in band sensing, output delays, and speed detection. It features a stainless steel barrel and a moisture-sealing, vibration-absorbing potting compound, and an extremely bright, 360-degree LED indicator. Auto-Configure technology lets it automatically detect whether it has been wired for NPN or PNP. Extended range is reportedly up to three times that of typical inductive sensors and inherent high noise immunity can be programmed up to 20 volt/m. iProx comes in Standard and Clone versions, with the latter adding built-in output delays and speed detection. Eaton Cutler-Hammer

Meeting diverse needs

Machine Control & Discrete Sensors

Simatic range of proximity sensors meets diverse requirements of the production industry. Devices can detect, measure, monitor, or position solid, liquid, pulverized, or gaseous objects. Family is designed especially for factory automation environments and includes inductive, ultrasonic, and optical devices. Line is said to offer exceptional reliability, high precision, high repetition accuracy, and long service life, yet tolerate a wide range of industrial environmental conditions. Siemens Energy & Automation

Self-teach capabilities

XS6 line of auto-adaptable inductive proximity sensors incorporates a self-teach mechanism to simplify set-up. Part of the Osiconcept line of photoelectric and proximity sensors and limit switches, it features fully shielded, metal-bodied cylindrical inductive proximity sensors with an increased sensing range. Products are available in sizes of 8, 12, 18, and 30 mm; all but the 8-mm version have self-teach capabilities. Options include two-wire ac/dc and three-wire dc versions with normally open or normally closed outputs and cable or connector versions, as well as PNP or NPN in dc models. Telemecanique/Schneider Electric

Five-beam wide-angle sensors

5-beam wide-angle sensors are said to be the first to provide area triangulation sensing capability. Part of the manufacturer's expanded line of distance measuring sensors, the devices offer a 25-deg wide measuring angle and come in three detection ranges from 4-300 cm. They have no moving parts, require little energy consumption, provide continuous distance reading, and feature low reflective interference. Applications include robotics and smart vending machines. Sharp Microelectronics of the Americas

Online Extra

The case for networking via I/O modules

Networked systems offer real advantages over non-networked ones. So says Mike Shu-lim, chief technical officer for DST Controls (, a San Francisco Bay area system integrator. “Until the 1980’s, system integrators were limited to hardwired I/O devices [sensors]. Each time the control strategy changed, or a system expansion was im-plemented, new sensors or additional I/O modules had to be installed or wires replaced or added. After all the changes were made, the system integrator would be employed to remap and reconfigure the controller logic.

“Troubleshooting a large hardwired (non-networked) system was, and still is, difficult due to the significant distances involved, the often awkward locations of field sensing de-vices, and the fact that hardwired-sensors normally do not provide necessary feedback for troubleshooting purposes—unlike that provided by sophisticated troubleshooting tools built into industrial network protocols,” Shulim continues.

So why not consider networking over hardwiring? Among the major advantages are savings on wiring—in most cases repeaters will be next to the installed sensor. No addi-tional PLC cards will be required, simpler PLC code modifications can be used, effective troubleshooting tools (network and end devices) are available, and the same network will accommodate control appliances from a large variable frequency drive to a $50 proximity switch.

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