The changing environment of discrete sensors

We've all experienced some sort of change within our lives that render us to question, why weren't things that way in the first place. Change, inevitably, is a part of life that helps you realize growth has occurred, for nothing is static. That idea rings true for various characteristics of discrete sensors.

By Antonia E. McBride, assistant editor July 1, 2001

We’ve all experienced some sort of change within our lives that render us to question, why weren’t things that way in the first place. Change, inevitably, is a part of life that helps you realize growth has occurred, for nothing is static.

That idea rings true for various characteristics of discrete sensors.

‘Over the last few years, sensors have become more intelligent through the introduction of microprocessors and specialized application specific integrated chips [ASICs], allowing for self-teach capability, ambient light immunity, and other benefits,’ says Jon Spry, marketing manager, presence sensing business for Rockwell Automation (Chelmsford, Mass.).

He adds, ‘Additional developments include minimization in sensor size while retaining sensing range and environmental ratings, and the introduction of laser light sources and color sensing,’ all contributing to changes in the industry.

Brian Tarbox, product manager, sensing division for Turck Inc. (Plymouth, Minn.) says other changes in sensor technologies include better noise immunity and a wider variety of packages, such as various cylindrical and rectangular sizes.

Research was undertaken by Cahners Research and Control Engineering to gain a better understanding of readers’ applications and needs regarding discrete sensors. One thousand surveys were mailed to subscribers and 218 were returned for a 22% response. Results below are based on 178 respondents who are involved in specifying, recommending, and/or buying discrete sensors for in-plant or OEM (resale) requirements.

Sensors most used

More than 90% of those surveyed say they use limit switch discrete sensors. Photoelectric, inductive proximity, safety switch, and capacitive proximity sensors are also used by over 60% of respondents. (See graph.)

Survey participants were then asked what styles of photoelectric sensors they use. Seventy-one percent indicate using retro-reflective sensors. Limit switch and through-beam represent a second tier of widely used photoelectric sensors.

Joe Dolinsky, sensors marketing manager, Banner Engineering (Minneapolis, Minn.) says, ‘Retro-reflective-type sensors are the best compromise of range and ease of use and will continue to be a mainstay. However, they are dependent on a quality signal to be returned to the sensor via the reflector, not an easy task in all environments.’

Rockwell Automation’s Mr. Spry agrees, adding, ‘Customers want to minimize components needed to solve an application. Additionally, determining the optimal location for a reflector, then mounting and aligning it costs valuable installation time. While diffuse sensors solve this problem, standard versions are not suitable for many applications due to their sensitivity to target and background characteristics. As a result, reliable background suppression sensors are emerging as the preferred solution.’

As reported in last year’s discrete sensor study, inductive proximity switches were used nearly as often as the limit switch. The tide has changed and photoelectric has gained in popularity among respondents.

According to Pam Naylor, product marketing specialist for solid-state sensors and limit switches, Schneider Electric/Telemecanique (Raleigh, N.C.), photoelectric sensors are used often in industry because they’re more versatile than inductive type sensors

‘Photoelectric switches are more affordable, more standardized, faster, and allow OEMs to save real estate on machinery,’ says Ms. Naylor.

Network and beyond

When asked which networks are applied with sensors, among the 26% of those who use sensors on a device network, DeviceNet is the most widely applied (by 69%). Profibus is used by 44%; Interbus, AS-i and Seriplex were used 29%, 13%, and 2% of the time, respectively.

Larry Fischer, marketing manager for Rockwell Automation’s sensing business, says, ‘As control systems become more and more distributed, the need for networked sensors will also increase.’ He adds, ‘Another growing trend is the use of IP67-rated I/O blocks on the factory floor that allow standard sensors to be connected to the network.’

Mike Frey, sensors product marketing manager for Omron Electronics (Schaumburg, Ill.) agrees, ‘Where networking is required, many users have chosen to use external equipment such as I/O modules. This allows users more freedom in selecting or changing networks without replacing sensors.’

Charlie Strobel, senior technical engineer, Keyence (Woodcliff, N.J.) says, ‘Device network is good with combining computers and other devices. Sensors incorporated in this network would be good if it allowed all types of sensors and not just the sensors that go with the network in use. The network should be standardized to allow it to grow to its fullest capacity.’

Future changes

Experts cited here agree that the future of sensing is ripe for continued change.

According to Ms. Naylor, sensors will become more and more sophisticated. She says, ‘For instance, color-recognizing sensors will see up to three colors at once, as if it were three sensors in one unit. [Schneider Electric] Telemecanique now includes Teflon-coated sensors that allow use of plastic in high temperatures and chemicals.’

Keyence’s Mr. Strobel says, ‘If I were to look into the future for the next type of sensor to be used, [it would be] the laser sensor. The reason is the increased detecting distance and small beam spot obtainable, while still having the response time and sensitivity of fiber-optic and photoelectric sensors.’

Rockwell Automation’s Mr. Fischer says, ‘The latest generation of smart sensors can be programmed to fit the application, and its teach-and-learn capabilities make setup a relatively easy task. These sensors are absorbing functions, like timers and counters, that formerly resided in the controller. In short, intelligent sensors are furthering the customer’s notion of true distributed control.’

Self-teachable for DeviceNet

Milwaukee, Wis. Rockwell Automation/ Allen Bradley has introduced the next step for DeviceNet 9000, self-teach photoelectric sensor. At the touch of a pushbutton, DeviceNet 9000 enhanced photoelectric sensor will learn the application being presented. This operation can also be activated over the network. Other features include selectable strobing or COS operating mode, advanced diagnostics (i.e., dirty lens), advanced logic (on/off/one-shot time delay), and mechanical node address setting.

Rockwell Automation/Allen BradleyCircle 374

Eliminate background interference

Minneapolis, Minn . Designed to eliminate background interference, Q60 adjustable-field sensors feature a mechanically adjustable sensing cutoff point that allows them to detect objects with relatively low reflectivity while ignoring background objects. Q60 sensing axis is defined by the location of three optical elements emitter, near detector, and far detector that line up across the sensor face. Applications include presence sensing, material handling, automotive assembly, and process control. The 10-30 V dc Q60 sensors have bipolar outputs; one NPN and one PNP, each rated for 150 mA maximum with 2 msec response time and repeatability of 500

Banner EngineeringCircle 375

Long range, embedded design

Minneapolis, Minn . Q80, a fully embedded proximity sensor, offers 2 in. of sensing range and dual diagnostic indicators. The dual diagnostic indication system provides a constant display of operating status visible from different angles, including above and below the sensor. The long sensing range allows positioning target objects farther from the sensor, avoiding impact damage and interference from moving parts. Q80 is reported to sense different types of metals at a single sensing range, including mild steel, stainless steel, copper, brass, and aluminum.

Turck Inc.Circle 376

More performance, low cost

Schaumburg, Ill. Omron Electronics E3X-NA Series fiber-optic amplifiers offer performance in a sensor designed for numerous sensing applications. The sensor body, 10-mm wide, snaps into place in a panel. Integral connectors allow mounting multiple sensors without the need for separate wiring between them. E3X-NA features a response time of 200s where large numbers of sensors are operating on different lines and/or different operational stages.

Omron Electronics LLCCircle 377

Long range, background rejection

Everett, Wa . E67 Long Range Perfect Prox sensor features background rejection and is designed for use in difficult sensing applications. Using Perfect-Prox technology, E67 sensors combine high excess gain and a sharp optical cutoff to allow detection of objects of any color or reflectance at a large target range, while ignoring all background objects beyond that range. Custom ranges, available from the factory, allow customers to match the sensor to the application. Models are available with both ac and dc operation in a single unit, up to 132 V ac and dc.

Eaton Cutler-HammerCircle 378

Three proxes in one

Florence, Ky . Triple-switchpoint Ultralinear analog inductive prox allows set-up of three programmable switchpoints anywhere along its 1-5 mm sensing range, providing three distinct on/off switching windows. Each switchpoint has a dedicated output line and output-on LED to alert control when the target is within operating window. Triple switchpoint sensors produce an analog signal with a linear output voltage proportional to the distance between sensor face and target. IP67-rated, triple switchpoint sensors have a nickel-plated brass M18 x 76 mm-long housing and operating range of -10 to 70 °C.

Balluff Inc.Circle 379