Non-contact sensor market touched by innovations

Sensors such as inductive proximity, capacitive proximity, photoelectric and ultrasonic are being used in many applications for which they were never considered previously. These noncontact sensors are available with a variety of output configurations, such as normally-open (NO) and normally-closed (NC) contact configurations, as well as analog output configurations.


Sensors such as inductive proximity, capacitive proximity, photoelectric and ultrasonic are being used in many applications for which they were never considered previously. These noncontact sensors are available with a variety of output configurations, such as normally-open (NO) and normally-closed (NC) contact configurations, as well as analog output configurations.

An inductive proximity sensor with an analog output, for example, could take the place of a traditional limit switch monitoring a cable pulley system (Fig. 1). The analog output could detect when the cable is starting to stretch and signal a maintenance person so preventive action can be taken instead of experiencing an unscheduled shutdown. Conversely, a limit switch may detect only when the cable is out of specification, or the switch may fail due to the wear and tear of being in physical contact with the cable.

Smaller is better

A recent advancement for noncontact sensors is the of "thin-is-in" concept. OEMs and end users are both looking for smaller and more accurate sensors. Market trends show that shape and size does matter. New technologies for the sensing circuitry as well as moldings for the housings are breaking application barriers.

New sensor features are creating another accelerating trend. Proximity sensors are starting to incorporate status LEDs that are visible 360 deg around the sensor (Fig. 2). Sensor manufacturers use LEDs to provide more information than just sensing indication. For example, a status LED can pulse to indicate a weak detection signal, possibly caused by a sensor coming out of adjustment, or by a foreign object such as grease covering the sensor surface.

Advancements such as these will enable users to diagnose possible problems. A trained maintenance person can observe the pulsating LED and take action before a process shuts down unnecessarily.

It's what's inside that counts

Sensors are taking their shape from the inside and changing their outside dimensions and mounting options. Sensor manufacturers are incorporating such technologies as application-specific integrated circuits (ASICs) to drive down the size and cost, and increase ease of use of sensors. Using ASIC technology, fewer components are required to control the sensing circuit. Combining a large number of components onto a single integrated chip allows sensors to achieve greater sensing distances — up to three times that of existing sensors — in a package smaller than 8 mm in diameter.

ASIC technology also increases sensor precision. Sensor manufacturers do not have to rely on special machines to "calibrate" a trimming resistor in order for each sensor to be within specification. The ASIC technology allows the sensors to be calibrated digitally with programming devices.

Sensors incorporating ASIC technology can be manufactured at a reduced cost by lowering the number of components needed to control the sensor and the reduction of labor required to assemble the units. Thus, these sensors cost less for both OEM and user. Sensor manufacturers can lower their inventory overhead because the sensors can be assembled quickly.

As the components of sensors shrink, the sensor housings become smaller. Current production methods such as gaskets, glue and epoxies are no longer the best choices. Designers now rely on such techniques as overmolding and ultrasonic welding. This type of fabrication provides tight seals and the rugged packaging needed in industrial environments.

Sensor types

With more functionality in a smaller package, those who used 30 mm sensors can now use 18 mm sensors; and the 18 mm sensors can be replaced with 12 mm units. The 12 mm sensors have become one of the most popular sizes, but now that 8 mm inductive proximity sensors have sensing distances up to 3 mm shielded and 4 mm unshielded, their market share is starting to increase.

Photoelectric sensors

The size of photoelectric sensors is also decreasing . The trend for these sensors is moving from the big rectangular-style package to a much more compact style in both miniature rectangular and round configurations. Benefits to machine builders include the ability to locate the sensors closer to their targets in order to use the full strength of the optics.

Where certain applications demanded installation of a sensing head connected to cables and a separate processing unit, smaller sensors can be mounted in tight and obscure places. In addition, the compact size still maintains the high reliability and durability needed for the industrial market.


The use of lasers in sensors offers great improvements in precise position detection, counting and inspection applications (Fig 3). These sensors are able to detect position changes in distances as small as the thickness of a business card. This helps users dramatically reduce process errors and prevent defective products from entering the marketplace.

Laser technology is also decreasing manufacturing costs and sale prices, providing inexpensive solutions to sensing needs that could not be met in the past.

Ultrasonic sensors

Ultrasonic sensors also are becoming smaller and more cost effective. They have a great advantage over typical proximity and photoelectric sensors because they have very good sensing ranges and are not as affected by dust or other environmental factors. Ultrasonic sensors are designed so there is almost no dead zone in the detection area.

Another advantage is that one ultrasonic sensor can be used for many materials without extra setup or sensing concerns. For example, an ultrasonic sensor can be used to detect a clear plastic film and the same sensor can then detect a red plastic film if required by the process. This type of dynamic operational change could be difficult if a standard clear-object-style photoelectric sensor were used.

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