Light Curtains - Delay that it is blocked according to Risk Assessment ?

Cydog · Mar 12, 2019

Good Afternoon,

We have a light curtain system that momentarily see's that it is blocked.
Is there an adjustment that you can delay , without risk , to delay the signal coming from the curtain to the safety relay or GuardLogix ? It seems like that time should be adjustable within reason .

Is that something you have come across before , and can it be done .

Thanks so much ,

LadderLogic · Mar 12, 2019

A typical safety application may use up to 500 ms delay in combination with an additional non-delayed signal. This way, when the light curtain is activated, the momentary signal will cause a controlled stop of everything that can be stopped via the PLC program (VFDs, servo drives etc.) and then, 500 milliseconds later, everything will be positively and safely disabled.

The delay MUST be implemented by means of a certified safety relay or a safety controller, not via a regular PLC or a simple relay.

Dravik · Mar 12, 2019

Part of calculating the Safety Distance for the light curtains is the Response Time for the safety devices.

If you add a delay before the safety devices react, you will change this calculation.

James Mcquade · Mar 12, 2019

ok, the light curtain is momentarily blocked.
the BIG question is, what is causing it to detect blockage?
are you feeding a part into the system.
is a hand, elbow, or other part of the body breaking the light curtain?

what is your application is another big question !

james

seth350 · Mar 12, 2019

Check alignment. Then check it again.
Easy way is to bump receiver or emitter and see if it blips.

JohnCalderwood · Mar 13, 2019

I remember using a light curtain system that you could teach/tune the beams to see and stop items with a certain pattern, and ignore others.

We used it to allow a fork truck to come in so far with his forks, but if he went too far, then it stopped the system.

Not sure if these are still available, as it was many years ago..........

slp530 · Mar 13, 2019

We had a light curtain that tripped intermittently mainly in the winter. We eventually traced it to birds flying through the beams to enter the factory. In summer the main roller doors are left open to allow some air movement.

ivo.maenen · Mar 13, 2019

I don't know if you mean to say that something is blocking your lightscreen and you would want to restore a normal state?

If so:

https://cdn.sick.com/media/docs/9/99/499
WHITE

Override is a manual triggering of protective field switching or muting after an error in the switching or muting conditions. A valid switching or muting condition is simulated briefly to switch or mute the protective device so that the system can be overridden or restored to an error-free status. Objects that have been left behind can be removed from the protective device area. This
function is primarily required whenever heavy objects are being transported and the transport device is shut down by the protective device.
Errors can occur due to a response from concurrence monitoring, a response from monitoring of the switching or muting time, as well as from direction detection, sequence monitoring, or sensor gap monitoring. Even the switching or muting sensors themselves or a restart following emergency switching off or a mains voltage failure can cause an error.

Aabeck · Mar 13, 2019

As John Calderwood notes I have used Banner light beams that have an allowed 'window' to be able to have small parts fed into the top die of a stamping press. It would allow up to 2" of the light to be blocked as the parts travelled up and down with the ram.

As for the OP maybe a window like this would work if the momentary blocking is small.

Light Curtains - Delay that it is blocked according to Risk Assessment ?

Cydog

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LadderLogic

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Dravik

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James Mcquade

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seth350

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JohnCalderwood

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slp530

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ivo.maenen

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Aabeck

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