Sensors Go the Small and Rugged Route

Photoelectric sensors provide key position information in industrial process control. Since these sensors are in the middle of the action, both small and rugged are critical factors. When an international protection (IP) rating of IP67 is standard, size, functionality and features become key differentiating factors. However, even rugged can be enhanced with chemical resistance capability or additional approvals from well-known rating organizations. In a 2007 survey of proximity sensors of all types conducted by Control Engineering, users ranked the following characteristics as important or very important:

1. Short-circuit protection;

2. Reverse-polarity protection;

3. Automatic sensitivity adjustment;

4. Corrosion resistance and

5. Washdown protection.

These three sensors provide a variety of examples for many of the above.

RUGGED PHOTOELECTRIC SENSOR

Totally encapsulated in a perfluoroalkoxy (PFA) jacket, Banner Engineering's WORLD-BEAM Q12 Series targets wet and corrosive industrial environments. The chemical-resistant, miniature photoelectric sensors have a 22- x 8- x 12-mm sealed housing and an IP67 rating and have been tested for 1,200 psi washdowns. Capable of sensing up to 1.5m in the opposed mode and 15, 30 and 50 mm in fixed-field ranges, the sensor is also available in polarized and non-polarized, retro-reflective sensing modes. Units have short-circuit protection, as well as protection for false pulse on power-up. Green and yellow LED status indicators identify power ON, overloaded, light sensed and marginal signal. Available in dark or light-operation models with bipolar NPN/PNP outputs, units mount directly on or inside manufacturing equipment in standard available mounting holes and come with either a 2 or 9m attached cable or 150 mm pigtail Pico-style quick disconnect.

MINI PHOTOELECTRIC SENSOR

With small parts conveying equipment in mind, Balluff designed the BOS 11K photoelectric sensor. The 34.5- x 29.3- x 15-mm T-style housing allows smaller machine designs for factory applications. Diffuse, retro-reflective, polarized retro-reflective and thru-beam styles are available in an ultrasonically welded housing. In addition to its IP67 rating, the sensor is UL and CSA approved. Units are protected from short-circuits, polarity, reversal and voltage spikes. LEDs provide enhanced diagnostics with a highly visible 360-degree LED window for easy troubleshooting. With the company's BMS mounting system, the sensors can be mounted in almost any position. The combination allows the sensor's use in flexible packaging, tabletop and general conveyor applications.

SMALL PROXIMITY SWITCH

With Ø 4 mm smooth and M5 threaded sizes, Lynch Electronics Series 1050 proximity sensors are promoted as the “smallest fully self-contained photoelectric proximity switch on the market.” Units have a stainless-steel housing. The use of parabolic mirrors instead of lenses for the optics allows vacuum-potting of the electronics and the optical parts providing ruggedness and IP67 protection. Chip-on-board technology instead of a ceramic substrate in the electronics portion provides greater shock and deformation resistance. Protective circuitry includes short-circuit, overload and reversed wires, as well as overvoltage protection from voltage spikes on the output and power supply. Proper operation is indicated by a yellow LED that lights when the output is switched. If the receiver has insufficient or excessive light, the LED flashes. The sensor's sensitivity is factory adjusted for operating distances of 20 and 50 mm.