Hand vs. Finger Clearance of a Safety Light Curtain

Safety Light Curtains are electro-optical devices that use one or more light beams to detect intrusions into hazardous areas. The light beams travel from an Emitter to a Receiver creating a securely controlled area. When any one of these light beams is disrupted, the transmitter will send an alarm signal to a safety circuit. This will let the machine know that an object, such as a finger or hand, has crossed into the restricted area. This results in an immediate shutdown of the machine.

The distance of one light beam to the next is referred to as the light curtain resolution. This distance determines what size an object must be to trigger the alarm signal and turn off the machinery. This is typically represented by a finger or hand, since these are the most common objects that will break a light beam circuit. The resolution for finger detection is 14mm. The resolution for hand detection is set to either 20mm, 30mm, or 40mm. These variations typically correspond to the distance the hazardous area is from the safety light curtain.

The closer the moving part of the machine is to a person, the closer the light beams need to be to each other. The Industrial Safety and Lean Manufacturing Experts must determine the optimal resolution of the light curtain that will work best for the operation of the machine and the safety of the personnel. This decision is based on three factors:

Resolution- What is the size of an object that can pass through the light curtain before an alarm signal is sent out.
Time- How long will it take the moving part of the machinery to stop, after the light curtain signal has been sent.
Distance- What is the distance of the moving part from the light curtain. Will the object make it to the moving part before the moving part stops?

Although finger protection carries the highest safety rating, it also has the highest cost. In many cases, based on the three criteria above, hand protection can be the most cost effective safety solution.

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