Pepperl+Fuchs Blog

Inductive Sensor Superheros: Stainless Steel vs. Plastic

Posted by Marcel Ulrich on Tue, Oct 09, 2012

In the 1930s, the creators of the comic book hero Superman decided to give him a descriptive title. “The Man of Plastic” was probably never in their top 100 choices, let alone top 10, and for good reason.

Stainless steel face proximity sensors

Plastics are great for use in many products and environments, but certainly not for surviving clashes with freight trains or super villains.

Now, making the unusual segue from comic book characters to industrial control, most inductive (metal-detecting) sensors utilize plastic sensing faces.  These products are a great, cost-effective option when the sensing area is relatively benign. But when selecting a model for use in abusive environments, where impact and abrasion are commonplace, the sensing face material-of-choice has now become metal – specifically stainless steel.

More so than other sensing technologies, inductive sensors feature comparatively short sensing ranges (often less than ½ inch). Such close proximity to the target object means even slight variations in target tolerances or vibration yield damaging physical abuse.

How is it possible, using inductive technology, to sense a metal through a metal sensing face? X-ray vision? Not quite. When the inductive sensor’s oscillator frequency is appreciably reduced, its sensing field no longer stops at a metal’s surface (in physics, known as the skin effect). It actually can penetrate and pass through certain metals. Stainless steel face sensors utilize this property to extend their detection field through metal, and detect a metal on the other side.

A simple conversion to a metal-face product can generate dramatic process improvements. Laboratory tests comparing the survivability of plastic- and metal-face products to metal brush abrasion and hammer impacts have shown stainless versions withstand exposure levels more than 20X beyond their plastic-face counterparts. I was privy to a customer application report that shows the 20X number can indeed even be much greater in specific applications. Considering stainless inductive sensor models cost only about 30% more than plastic models, it is easy to see why they’re becoming an increasingly used sensing alternative.

Increased machine uptime, fewer rejected parts, increased quality, reduced maintenance and troubleshooting, and reduced spare parts inventory are tangible benefits of stainless steel face proximity sensors. With modern metal-face designs featuring extended sensing ranges, there’s also no tradeoff of durability vs. sensing distance. Metal-face products carry virtually no performance sacrifices.

While the availability of superheroes to protect machinery from downtime is limited to the imagination, metal face proximity sensors offer a real solution to frequent proximity sensor wear and damage.

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Topics: Inductive Sensors

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