2021-09-14

Light curtains & barriers - All you need to know

We at OEM Automatic are specialists in machine safety and can advise and provide you with a whole host of safety equipment from a wide range of established manufacturers. Part of our machine safety range includes a large selection of safety light curtains and light barriers. But which of these suits your machine or application best? Read more about the different variants below. Do not hesitate to contact us if you have any questions.

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What is a light curtain and light barrier?

Light curtains or light barriers are also often referred to as safety light curtains. They are photoelectric safety devices which provide protection from hazardous machinery and are capable of monitoring large areas.

Light curtains consist of a transmitter and receiver. From the transmitter, infrared beams are transmitted to the receiver. When one or more of the light beams are interrupted, a duel output stop signal is given to stop the dangerous action of the machine.

The duel output signal consists of two separate OSSD = Output Signal Switch Device, ie two fail-safe 24Vdc outputs, these outputs are short-circuit monitored.

There are different systems to choose from depending on the function and requirements of your application. The safety requirements are set in international standards. There are different levels of security depending on the type of risk.

NOTE! Ordinary "standard photocells" do not have the required precision and should therefore not be used in security applications.

When are light curtains and light barriers necessary?

When there is a need for continuous access to an area of risk, e.g. loading/unloading of manually operated machines
When you need to secure large areas around hazardous machinery
For continuous goods passage (eg. Pallet of goods on a conveyor)
For machine safeguarding and access control in dangerous areas

Datalogic safety light curtains, light barriers and controllers

What is the importance of the resolution of your safety light curtain/barrier?

A light curtain has multiple light beams, which makes it ideal for the detection of small objects such as fingers or hands. The resolution of the safety light curtains relates to how close the light beams are together. 14mm resolution is designed to detect fingers, 30mm resolution is to detect hands or larger parts of the body.
Pedestrian access light curtains are usually 2/3 or 4 beams.

Resolution R = I + D (where: I = Interaxes between two adjacent optics & d = Lens diameter)

Datalogic safety light curtain finger protection

Datalogic safety light curtain hand protection

Various safety functions of light curtain/barriers

Bypass "mute"

In some applications and automatic processes, for practical reasons it may be necessary to disconnect the safety function of the light shield. The use of a mute on light protection requires a risk assessment of the machine to find out if there are any risks with bypassing the light protection. Bypass can be used in the following circumstances:

Material that affects light protection when input or output in the automatic process
Material handling requires the operator to be positioned so that the light protection is affected
The machine is in safe position

To achieve safety, a duplicated and monitored bypass system with at least two mutually independent signals is required. The performance level of the safety-related parts that make up the muting function shall be selected so that the introduction of the muting function does not lower the required safety level for the relevant protection function.

Manual start function

When a light barrier / light curtain is broken, a stop signal is given to dangerous machines within the risk area and a reset light comes on. To restart the machine, the light bar / curtain must first be reset.

This is done with a reset button that must be positioned so that it cannot be reached from inside the protected area.

Great demands are placed on the reset function. That is, neither a short circuit nor component failure must provide automatic reset.

When the reset button has been activated, the outputs are activated and the reset light goes out.

NOTE! Resetting the safety circuit should only allow the machine to be restarted.

Fixed / Floating Blanking

Blanking makes it possible to disconnect one or more beams from the protection field of the light shield. The purpose of this is to allow e.g. tools and material feeds pass the protective field without sending a stop signal to the machine. Available in two versions, Fixed and Floating blanking

Fixed Blanking

In "Fixed blanking" the object can not move in the protection field, but the same beams must be blocked at all times. If one e.g. removes the object, a stop signal is sent to the machine.

Floating blanking

Floating blanking makes it possible to disconnect up to three beams from the protective field. The object can then move in the protective field without a stop signal being sent to the machine.

NOTE! It is important to keep in mind that the resolution will be higher and that you must recalculate the protection distance.

Mute Enable

Acts as a third muting signal. In other words, a signal that enables muting. This function can be good to use in transport paths when connected to the motor contactor. When the track goes, a signal is given to the light protection that muting is possible. In this way, it is difficult to manipulate the protection and to enter a dangerous area.

EMD - External Device Monitoring

External contactor monitoring. 1 NC contact from the contactor is connected via 24v to a dedicated input on the light curtain. The light curtain cannot then be reset if one or more contactors have welded.

Override

Override makes it possible to temporarily drive the safe outputs of the light protection for a fixed period of time to a "mutated" position even when one or more safe beams are blocked due to errors in the muting sequence.

For example, a pallet gets stuck in the protection field, whereby the safe exits are broken and a stop signal is given. As long as the pallet blocks the protection field, it is not possible to reset the light protection.

Activation of the Override function enables the protection of the light protection

Cascade coupling

By cascade connection is meant that you can connect several units in series. You always start from a master that is connected in the safety circuit and the so-called slave is controlled by the master. Typical application is the so-called "L" variant.

Light curtains can be used in two ways, vertically and horizontally.

Vertically mounted light curtains are usually used to detect fingers and hands, or for pedestrian access control.

Horizontally mounted light curtains are most commonly used to detect a person standing in front of a dangerous machine.

Features of safety light curtains:

Blanking / muting
Range 60 m
Cascade coupling
Finger / hand protection
No need for software
SIL 3 / PL e
Protective field, 150-1800 m

You can see a selection of the Datalogic range of safety light curtains plus all the technical data on each of them below. See the full range of light curtains and accessories here.

Our sensors and safety team are on hand to discuss which safety products would be best suited to your applications. We can create a specific list of required components to take out all the guess work and make life easier for you.

Find full datasheets, installations guides and certification under 'downloads' on each product.

Email: [email protected] or call +(0)116 284 9900.