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Pepperl+Fuchs Blog

Industrial Light Grids vs. Safety Light Grids

Posted by Zach Steck on Thu, Jun 27, 2013

When it comes to determining which type of light grid is best for your application, there are a few questions to consider:

Industrial Light Grids vs. Safety Light Grids

What is a light grid?

A light grid consists of a transmitter and receiver unit with a large number of infrared through-beams that create a two-dimensional detection field. This parallel array of beams is used for monitoring large areas with field height options from 100 mm to 3200 mm. Though they have a simple design, these light grids offer numerous features, including:

  • Teach-in function capabilities for fast adjustments
  • Large light beam angles for quick and easy alignment of the two units
  • Beam crossover to increase the resolution of the light grid
  • Automatic calibration of the signal strength to ensure accurate operation in dirty or dusty environments
  • Functional safety requirements (Safety-rated light grids only)

Light grids are available with many different resolution options so that you can precisely detect objects of different sizes. Resolution refers to the distance between the beams—the closer together they are, the higher the resolution. High-resolution models can detect very small objects as well as transparent targets with high excess gain. Light grids are used in the following applications:

  • Door control in elevators
  • Small parts detection
  • Monitoring transparent foils in packaging machines
  • Web break detection
  • Profile and height control of pallets in material handling and conveying
  •  Personnel protection (safety light grids)

What is the difference between a safety light grid and an industrial light grid?

A safety light grid is used in any application where the light array is protecting a person. A safety light grid’s main function is to provide a stop signal to the machine control system when a body part or object enters the protected area.

The biggest difference between a safety light grid and an industrial light grid is that a self-evaluation system monitors the safety grids. Safety light grids are available with an optional relay monitor. The relay monitor is designed using force-guided safety relays so the receiver can check for the correct operation of the relay contacts.  When a normally open (NO) contact welds, the mechanically linked contacts prevent the reclosing of the normally closed (NC) contact. Similarly, when a NC contact welds, it prevents the reclosing of the NO contacts. This feature guarantees that if any of the contacts weld, the relay will not be energized.

If the safety light grid does not have the relay monitor option, you must use a separate safety controller. This safety controller also functions on the principle of self-evaluation and ensures the safe operation of the grid. If any problems are detected in the internal circuitry of the safety light grid by this controller, the machine shuts off, leaving it in a safe state. This feature protects the operator and any other employees from harm due to possible electronic failures of the light grid itself. The safety light grids and safety controllers have third-party approval for functional safety from certification organizations such as TUV.

Is a safety light curtain the same thing as a safety light grid?

In a safety application, light curtains are high-resolution light grids with narrow beam spacing for the protection of hands and fingers. Safety light curtains are available with 14 mm or 30 mm spacing between the light beams. Safety light grids are for body detection or perimeter guarding. These grids are made up of 1, 2, 3, or 4 beams that are 300 mm … 500 mm apart.

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Topics: Light Grids

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