The safety of plant personnel must be maintained as the top priority in any working environment. Those who work with and on machines, automated equipment and robots are often unaware of the dangers involved. However, the potential impact on the health and safety of all users can be devastating. As is so often the case, prevention is the best protection! You need the right safety technology. In this guide, you will learn why safety light curtains are the best solutions for bodily protection and which important selection criteria and installation instructions must be taken into account.

Why is it important to use safety light curtains to protect hazardous areas?

Figure 1: The risk of injury in manufacturing processes is very high. Source: Automation24In manufacturing processes, hazards from machines lurk around almost every corner. Manual workstations and test stations such as presses, cutting, bending and punching machines pose a particularly high risk. Without appropriate protective measures, users can all too quickly come into contact with moving machine parts. The consequences are cuts, bruises, fractures, sprains – or even worse.

To prevent this from happening in the first place, it is essential to safely detect when fingers, hands and other limbs enter hazardous areas. In this way, dangerous machine movements can be switched off automatically. Safety light curtains are an ideal solution!

What are safety light curtains and how do they work?

Figure 2: Safety light curtains consist of a transmitter and a receiver unit. Source: Automation24

Safety light curtains are optoelectronic safety sensors. They consist of a transmitter unit and a receiver unit and operate on the same principle as through-beam photo- electric sensors, which are used especially for position detection.

Unlike conventional light barriers, however, safety light curtain transmitters send a large number of light beams at defined distances to the receiver module. This creates a virtual and very tightly meshed barrier for protecting hazardous areas. As soon as fingers, hands or other limbs penetrate this barrier and interrupt the light beams, the dangerous machine movements can be automatically switched off. This explains why safety light curtains belong to the category of electro-sensitive protective equipment (ESPE).

Another important difference from standard photoelectric sensors is that, as safety sensors, safety light curtains have the necessary features to prevent unexpected

What are the selection criteria for choosing the right safety light curtain?

Selecting the right safety light curtain is very simple. You‘ll be on the safe side if you consider the following three or four selection criteria:

Figure 3: Safety light curtain – construction and selection criteria. Source: Automation24

Safety light curtains have other design features which may cause them to differ from one another. These include, for example, an extremely narrow design or the absence of a dead zone. However, these distinguishing features are relevant for very few applications, which is why they are intentionally not discussed in detail here. In most cases, standard light curtains are perfectly adequate.

In comparison: safety light curtains and safety light grids

The terms safety light curtain and safety light grid are often mistakenly used interchangeably. However, this is incorrect. Although they differ very little from each other externally, there are significant differences in their characteristics and their suitable areas of application.

Figure 4: Protecting hazardous areas with a safety light grid. Source: Automation24

One of the most significant differences is their resolution. While light curtains generate a large number of light beams at small distances, light grids usually generate only two to four light beams at significantly larger distances. This is because of the different applications for which they are designed. While safety light curtains are used for finger and hand protection detection in hazardous areas, light grids are used to protect larger areas, where body detection using fewer light beams is sufficient.

This is because of the different applications for which they are designed. While safety light curtains are used for finger and hand protection detection in hazardous areas, light grids are used to protect larger areas, where body detection using fewer light beams Is sufficient.

In comparison: safety light curtains and safety light grids

Figure 5: Area protection with a safety light curtain. Source: Automation24

Area protection is often important for logistics applications. In this context, muting is also an important requested feature. Muting makes it possible to temporarily bypass light curtains, for example, to move pallets out of the hazardous area without bringing system processes to a standstill. Immediately after the pallets have been moved, the light curtain is reactivated to detect people entering the hazardous area again.

When protecting hazardous areas with light curtains, a muting feature is not usually needed because materials are rarely moved out of the hazardous area.

How do you properly install and test safety light curtains?

Before they can be used, it is important to install safety light curtains correctly and test their performance.

Choosing the correct minimum distance

It is very important to maintain the correct minimum distance between the light curtain and the hazardous area. The rules for this are clearly defined in the DIN EN ISO 13855 standard.

S = Minimum safety distance A = Danger zone Figure 6: According to DIN EN ISO 13855, a minimum distance must be maintained. Source: Automation24

Light curtain safety distance – calculation formula:

S = K * (t₁ + t₂) + C

S = Minimum safety distance

K = Approach speed

t1 = Light curtain reaction time

t2 = Machine reaction time until standstill

C = Maximum distance of undetected movement behind light curtain

K and C set the standard.

K as gripping speed = 2,000 mm/s,

if the result of this formula is greater than 500 mm,

K = 1,600 mm/s (step speed) may be used.

C equals 8 * (resolution (d) - 14 mm),

when using a 14 mm light curtain, C = 0 mm, and when using a 30 mm light curtain, C = 128 mm.

The following formulas are derived from this:

For 14 mm resolution light curtains: S = 2,000 mm/s * (t

₁+t₂)
For 30 mm resolution light curtains: S = 2,000 mm/s * (t₁+t₂)+ 128

How do you properly install and test safety light curtains?

Bypass protection

When properly installing a safety light curtain, it is imperative that all limbs entering hazardous areas are detected without exception. The prerequisite is the correct selection of the appropriate protective field height so that it is not even possible to reach past the light curtain into the hazardous area.

It is also necessary to make sure that no one can remain undetected behind the light curtain. Therefore, if an application requires a very high safety distance, it is essential to install an additional horizontal light curtain.

Correct versus incorrect types of mounting

Figure 7: Installation at low safety distance. Source: Automation24 Figure 7.1: It must not be possible to reach past a safety light curtain. Source: Automation24

Alignment guide

Because the light beams emitted by the light curtain are not visible, it can be very difficult to align the transmitter and receiver over long ranges. Mounting laser pointers on the transmitter can help with alignment.

Protection against vibration

Safety light curtains are designed to cause machines to shut down as soon as the light beam sent by the transmitter cannot reach the receiver. However, machines that vibrate strongly can disrupt the light beam, because the vibration can cause the transmitter and receiver not to be aligned with one another momentarily. As a result, vibration-heavy applications require the use of special vibration dampers to prevent unnecessary triggering.

Daily operational tests with test rods

Trust is good, monitoring is better. This also applies to safety light curtains! To check for correct operation and to reduce the risk of liability in the event of a malfunction, it is recommended to perform a daily operational test on each safety light curtain.

For this purpose, a test rod is passed through the protective field to check that the light curtain beams are interrupted correctly. The test rod must have the same diameter as the resolution of the light curtain.

Protect yourself and your employees with light curtains

Security technology should not be a luxury. Don‘t take your health or the health of your employees lightly. Rely on dependable safety light curtains for your protection!

With this compact guide, you are now ideally equipped to select the right safety light curtain for your application and to install it in compliance with standards.