Understanding Factor 1 sensors: When and where to use

March 1, 2011
Non-contact proximity sensors can improve the ruggedness of manufacturing operations, such as metal component assembly, by replacing delicate mechanical

Non-contact proximity sensors can improve the ruggedness of manufacturing operations, such as metal component assembly, by replacing delicate mechanical switches. Sensor selection for these applications is based on several factors, including the types of metal to be detected, information required about the target (simple presence or absence, or exact position), and environmental conditions.

Inductive proximity sensors are commonly used for metal component detection due to their non-contact operation. Traditionally, these sensors feature a coil wrapped around a ferrite core, an oscillator, detector circuit, and solid-state output. They generate a high-frequency electromagnetic ac field that interacts with the target. When a metallic object enters this field, the sensor's output signals that the target is present, so the machinery reacts accordingly — for example, to divert a product from an assembly line or send it along to the next production stage. Unlike mechanical switches, inductive proximity sensors have no moving parts — a design that reduces wear for increased operational life.

Sensing different types of metals with traditional ferrite core technology is difficult without physically moving the sensor, because various metals induce different responses. Therefore, sensors for these situations are programmed to sense whatever metal type is being detected. Some applications require that two different metal types, such as mild steel and copper, be detected on the same line. In these cases, the sensor more readily detects the presence of steel, whereas copper may not contain enough ferrous material to activate the sensor at the same rated distance. Here, a standard ferrite core proximity sensor must be relocated to adjust its sensing range in a way that accommodates these varying materials — what is known as a correction factor.

A better solution is to use a factor 1 sensor to sense ferrous and non-ferrous metals alike — from aluminum to copper and stainless steel to brass — all at the same rated distance. These sensors replace the single coil in ferrite core proximity sensors with separate, independent sender and receiver coils on a printed circuit board. This design ensures various metals can be detected with no sensor adjustments required, reducing downtime during product changeover and saving installation costs.

Along with their non-contact operation, proximity sensors are often equipped with rugged housings to resist harsh plant conditions. Many inductive proximity sensors are sealed to prevent moisture or contamination from entering the device. Some are also rated IP68 or IP69K for applications where the sensor may be submerged or subjected to high-pressure spray. What's more, factor 1 sensors deliver an additional environmental advantage due to their unique design: As most of these sensors are made without a ferrite core, they are immune to magnetic field interference.

This month's handy tips courtesy of Brian Tarbox, TURCK Inc.,, (800) 544-7769.

Product gallery: Proximity sensors

Food and beverage sensors rated to IP69K

Compliant to IP69K, a new line of food and beverage sensors withstands washdown conditions to 212° F and is made of FDA-certified materials. PFM 12-mm and PFK 18-mm proximity series are sensors with shielded or unshielded stainless steel housings and M12 quick-disconnect plugs with gold-plated pins. The PFM series has a standard sensing distance to 4 mm and extended distance to 8 mm. The PFK series has a standard sensing distance to 8 mm and extended distance to 12 mm. PFT 30-mm series proximity sensors feature sensing ranges to 22 mm. VFK 18-mm and VFT 30-mm series proximity sensors are available with shielded or unshielded stainless steel housings and half-inch micro ac quick-disconnect plugs with gold-plated pins. Magnetic proximity sensors are available in 12 and 18-mm diameters. The shielded 10 to 30-Vdc sensors have a sensing range to 70 mm. Two series of 18-mm food and beverage photoelectric sensors have also been added.

Contact: AutomationDirect • (800) 633-0405 •

Prox sensors mounted directly on actuators

Integrated end-of-stroke proximity sensors are now available on 25000 Series 1-in. captive linear actuators. The sensor uses miniature Hall effect technology in an IC package mounted directly on the actuator, enabling a virtually unlimited on-off cycle life due to non-contact operation. The Haydon can-stack linear actuator with integrated sensor is suited for limited space applications. A highly repeatable on/off signal is accomplished using a rare earth magnet embedded directly on the end of the internal screw: As the screw moves in and out of the actuator, the magnet moves toward and away from the sensor face causing the device to switch states. The proximity switch is a 3-wire device and requires a supply voltage of 3.8 to 24 Vdc with a current consumption of 10 mA maximum.

Contact: Haydon Kerk Motion Solutions Inc. (203) 756-7441 •

Capacitive sensors suit object and level detection needs

The Global.CProx family includes a wide array of tubular M12, M18, and M30 sensors available with either M12 connectors or pre-wired cables. All sensors offer reverse polarity and short circuit protection with enhanced EMC protection. Flush-mount versions of these sensors can detect objects up to 15 mm away, regardless of color, texture, or material. Non-flush mount versions are suitable for level detection of bulk material or liquids either directly or through a plastic or glass container wall, with sensing distances to 25 mm. These economical sensors feature stainless steel or plastic housings, high EMC noise immunity, extended switching distances, and a wide sensitivity range.

Contact: Balluff Inc. • (800) 543-8390 •

Distance measuring sensors fit tight spaces

The IWFM 08 inductive sensor can be easily integrated into any design due to its compact outer dimensions of just 8 × 16 × 4.7 mm; a sturdy metal housing holds all the electronics. Within the photoelectric range, the OADM 12 is one of the smallest available laser distance sensors featuring an integrated evaluation unit. Despite its compact housing, the sensor measures with a resolution of 2 µm, independent of object color and material, over a measuring distance to 120 mm. It is suited for high-precision positioning or profile measurement, such as quality inspection. The UNDK 10 ultrasonic sensor is also one of the smallest sensors of its kind: A very narrow sonic beam angle allows for liquid level measurements — even in containers with small openings — to a measuring distance of 200 mm.

Contact: Baumer Ltd. • (800) 937-9336 •

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