Light Curtains by ABB Safety
What is the difference between a light curtain and a light grid?
A light curtain has several beams that are placed closely together whereas a light grid consists of only one, two, three or four light beams. The beams are closest on a light curtain that is used for finger detection. Then the resolution is 14 mm. For light grids the beams are normally placed at a relative distance of 300 to 500 mm.
The choice between light grid or light curtain is often a question of available safety distance, reach and price. Light curtains are often chosen for short safe/minimum distances. Light grids are chosen for longer safe/minimum distances, long range up to 40 m and for a low price.
Blanking
Blanking means permanent switching off of a number of beams in the detection zone of a light curtain. This is a function that is permitted and used when an object that is larger than the resolution of the light curtain is permanently located in the detection zone, without deactivating the safety outputs (OSSD). If the object is removed from the detection zone, the safety outputs are deactivated.
Blanking function has different tolerance settings that allow movement or vibration of the objects that obscure the detection zone.
One tolerance setting can be called ”Floating blanking”, that means that the part of the zone which is intentionally blocked can be moved around in the detection zone while the machinery is operating. Other beams are active and providing normal protection, but often with reduced resolution.
When a “blanking” function is used, it is very important that the light curtain provides protection and can detect objects, as small as a finger or hand, depending on the resolution, anywhere outside the zone that is rendered inactive because the object is there. Blanking may require an additional fixed guard and may require additional minimum distance to the dangerous movement.
It must not be possible to select the “blanking function” without using a key, tool or similar unlocking device.