Light Curtain vs. Safety Scanner

jrexrode

Member
Join Date
Mar 2005
Location
Upstate, South Carolina
Posts
106
I'm hoping someone here with more knowledge of this than me can help answer this. Would there be any effect on the safety of a machine if a laser safety scanner is used to guard the entry point of a machine instead of light curtains. The specifics are that the scanner is a SIL 3, Category 3 device, while the curtain is SIL 3, Category 4 device. Assuming that both devices would be interfaced to the machine the same way with each of the two safety outputs energizing a seperate force guided relay with monitoring, how is one better than the other? The reason for asking is that I have bought and installed a laser scanner on a machine to replace a light curtain, and I am now having to defend why the scanner is as safe.
 
It may be time to pull out the books and show the big wigs the safety standards for Category 3 and Category 4. You should be able to pull this information from the device manufacturer.
 
I'm hoping someone here with more knowledge of this than me can help answer this. Would there be any effect on the safety of a machine if a laser safety scanner is used to guard the entry point of a machine instead of light curtains. The specifics are that the scanner is a SIL 3, Category 3 device, while the curtain is SIL 3, Category 4 device. Assuming that both devices would be interfaced to the machine the same way with each of the two safety outputs energizing a seperate force guided relay with monitoring, how is one better than the other? The reason for asking is that I have bought and installed a laser scanner on a machine to replace a light curtain, and I am now having to defend why the scanner is as safe.

I sympathise! We have an AGV at work which collects 1 tonne pallets of product and takes them from the robots to an automatic spin wrapper. Because pedestrians and the vehicle use the same path it is fitted with two Sick laser scanners, one either end.

They are far more sophisticated than a light curtain and their range and detection pattern is speed dependant.

We test the vehicle safety systems weekly and have never had a scanner failure (Most systems fail to safe) in 10 years..

I even stand in front of it to prove it stops!!!
 
Tharon, It's a trimming operation powered by hydraulics. It is surrounded on 3 sides by a cage and has a non-monitored hardwired e-stop. The laser scanner controls the 2 MPCE relays, which in turn switch the output voltage for the valves. The danger is of course an operator getting their hand under a cutter and losing a finger. I myself know little of the different safety category levels other than that 3 and 4 are the "safest", and that your safety level is only as good as the weakest device in the system. Frankly, I find the stated difference between a type 3 device and a type 4 device as given by the technical papers confusing as hell.
 

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