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How Safe is your Safety Device?

by Rod Karch, Safety Specialist at Leuze electronic USA
Leuze Electronic, Inc.

It is typical when implementing safety products for a machine or process that you choose a device based on the application need. Most safety devices are available in several categories (i.e. category 1-4) in order to fill the application safety requirement.

Leuze SLE46C-40.K4/4P - Single beam safety device

Above: Leuze SLS46C Single beam safety device. Safety Category Type 4 PL d/e

While a device is rated for a specific safety category, what does that mean? How safe is the device really? For the answer to this question lets take a look at some examples...

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  1. Safe driving requires proper tires and braking systems along with an adequate driver.
  2. A secure home requires doors and windows that are in working condition closed and locked.
  3. Living a healthy life requires food with proper nutrition and exercise.

In all the examples above the pieces are part of a whole, without one piece the system integrity fails. One cannot drive safely on bald tires, even if the driver is very skilled. A home is not safe if the windows are locked but the panes are broken. It is not healthy living if one exercises regularly but the only food eaten is junk food. The same is true for safety products!

A safety device is only as good as all the pieces of the system it is integrated into. This means that safety-rated devices wired into a standard relay nullifies the safety rating and provides no safety benefit. Some examples that I have experienced:

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  1. Use of a safety device wired into a standard non-safe "standard" PLC.
  2. Bypassing a safety device in a circuit, provided a false "safe" signal.
  3. Running multiple devices in series that are not series compatible (i.e. non-contact safety switch).

So when designing a safe system, please keep in mind all the components along with the safety circuit design as they all constitute a whole. There are many regulations that provide information on how to design a safety system (i.e. OSHA, ANSI, NFPA) please find specific code information on our website or feel free to contact Leuze directly for assistance.

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