Safety Light Curtain Basics: What Is a Safety Light Curtain?
Safety light curtains are safety devices designed to guard potentially dangerous machinery and protect the individuals who will be working with these machines. One of the advantages of these light curtains is that instead of being a bulky mechanical guard, they’re relatively small and unobtrusive. Instead of protecting simply because of their bulk, they work with a little more finesse.
Safety light curtains are essentially presence, or motion, sensors. This means that they create a curtain of photoelectric light beams between an emitter and a receiver that then sense whenever an object intrudes into this light field. This means that they work by detecting potentially harmful machine motion, or detecting human movement in an area where there should not be. In this way, they help to add an extra layer of security around potentially dangerous machinery.
There are two varieties of safety light curtains. These varieties are based on the scale of protection they provide.
- Point of Operation Control (POC) safety light curtain: These light curtains are designed to protect on a small scale. Specifically, they help protect hands, fingers and arms that are going to be operating the machinery. These light curtains are generally located very close to the machine, directly where the worker will be interacting with it.
- Perimeter Access Control (PAC) Safety Light Curtains: These PAC light curtains differ from the POC variety in that this style offers full body protection. They essentially create a fence around machines that don’t require up-close usage by workers, and are designed to detect people or objects when they intrude into the light barrier.
Both POC and PAC light curtains work in the same way. The only real difference between them is their size and scale which makes them appropriate for different situations.
Type 2 vs. Type 4 Light Curtain
Not only do safety light curtains break down into POC and PAC varieties, but they break down further into different groups known as Type 2 and Type 4. These two types might look similar, but differences between them are significant. At their core, the difference between Type 2 and Type 4 light curtains is rooted in the fact that they’re simply designed to satisfy very different levels of safety requirements.
Safety light curtains type 4 are needed when the level of risk is much higher, and are subject to much higher safety standards. Safety light curtains type 2, on the other hand, are designed for situations where the level of risk is considerably lower. Therefore, they have fewer safety features and can’t be used in situations where a Type 4 light curtain is called for.
Broken down, here are some of the major differences between Type 2 and Type 4 light curtains.
- Fault Detection
- Type 4 light curtains are characterized by repetitive, automated cross-checking for faults and errors. If a problem occurs, the Type 4 will notice it immediately and send a signal to the machine, sending it into lockdown mode. The machine won’t resume until the affected part has been inspected and possibly replaced, and the system has been reset.
- Type 2 light curtains are not nearly as rigorous. They run tests on their internal circuits periodically, with gaps in between where no testing or checking occurs. This means that if a problem arises, it won’t be detected until after the second test. This doesn’t mean that Type 2 light curtains are ineffective — it just means that they’re only appropriate for situations where the level of risk is far lower.
- Field of Vision
- The field of view of the emitter and the receiver is known as the effective aperture angle, or the EAA. Type 4 light curtains have EAA of ±2.5 degrees, whereas Type 2 light curtains have the wider angle of ±5 degrees. With this wider EAA, Type 2 light curtains are ultimately more likely to experience an optical short circuit.
- An optical short circuit is when an extremely reflective surface gets caught in the light curtain’s field of vision, and may deflect one of the light curtain’s sensing beams. This has the potential to affect a light curtain’s ability to sense an object passing through the light field. Because the Type 2’s EAA is larger, there is a greater possibility of this occurring. Simple tests can be performed at the time of installation to ensure that this error is not occurring.
- As might be expected, the third difference is in price. Because Type 4 light curtains offer more features and are designed to fit a higher safety standard than the Type 2, they are ultimately more expensive. As a general guideline, the average Type 4 devices can be anywhere from 15% to 30% more expensive than the average Type 2 device.
- Available Varieties
- Type 4 light curtains are available for body, hand and finger protection. Type 2 light curtains have fewer options and are only available for hand and body protection, so they do not offer the minute level of detail needed for finger protection.
- Methods of Usage
- Sometimes when extra safety is required, a Type 2 light curtain will be used as a secondary level of protection, in addition to other safety measures. This does not mean that Type 2 light curtains are never used on their own as the primary means of production, but that they are also occasionally used as the secondary safety measure. Type 4 light curtains, on the other hand, are almost exclusively the primary safety measure, and would rarely be used in this more secondary role.
Essentially, a Type 2 Light Curtain is a less expensive version of the Type 4 Light Curtain. It has fewer capabilities and fewer safety protocols, making it an affordable option for low-risk situations where a Type 4 light curtain is unnecessary.
Type 2 light curtains are only appropriate for situations where the worst-case potential injury could be easily remedied with a first aid kit. Type 4 light curtains are suitable for situations where the potential injuries would be far greater.
What’s the Difference Between a Type and a Category?
“Type” and “Category” might seem like synonyms, just redundant names for the same thing. But in the case of safety light curtains, they refer to two very separate things.
The term “category” refers to the machine itself, and the way it interacts with protective equipment. “Type” refers to specific design, construction and testing requirements of the light curtain itself. Essentially, they’re safety standards. For example, a Type 4 device would be most likely to be used in a Category 4 application, and a Type 2 light curtain could probably only be used for a Category 2 application, but only if it is used as the primary safety guarding.
Deciding which type of light curtain you need isn’t simply a matter of deciding which you prefer. There are safety standards that have to be met, per the guidelines and regulations set out by the Occupational Safety and Health Administration (OSHA).
OSHA has a list of regulations that need to be complied with when it comes to selecting a light curtain. The simple breakdown of those regulations, as found on OSHA’s website, is as follows:
- Light curtains must comply with IEC-61496 parts 1 & 2 adopted as ANSI/UL 61496 parts 1 & 2.
Let’s break each of those pieces down a bit more.
- IEC-61496 parts 1 & 2 are essentially safety standards for electro-sensitive protective equipment (ESPE). These parts relate to the functional and electrical safety features for safeguards that sense the presence of a person. This applies to not only light curtains, but also to things like laser scanners and optical actuators. In other words, there are certain safety standards that have to be met for a light curtain to even be available on the market, as laid out in IEC-61496 parts 1 & 2. Before this standard was adopted, there wasn’t a standard for such protective equipment. As such, this standard was adopted due to the sheer number of malfunctions and failures in devices such as light curtains in the past. This new standard ensures that light curtains can maintain all safety functions even when they’re subjected to environmental complications such as light interruptions and electromagnetic interference.
- When the guidelines say that the type must be appropriately selected, this is referring to the differences between Type 2 and Type 4. One can’t be used where the other is appropriate. To reiterate, Type 4 is appropriate for machines with a higher level or risk, while Type 2 is suitable for lower risk levels.
- A light curtain’s optional functions must be in compliance with IEC-61496. Again, this is the same information as in (1). It simply is restated here that even the optional functions are not exempt from this high standard.
- Light curtains must be properly integrated into the machine. This point is self-explanatory.
- An independent third party must certify the light curtain. A manufacturing company cannot, for instance, certify their own light curtain. The third party must be uninvolved, and must certify that the light curtain is indeed up to standard.
All of this might seem like it would be extremely difficult to keep track of, but there’s a quick and easy way to tell if a light curtain meets these standards. If a light curtain is up to OSHA standard, it will state on its product label:
- Standard IEC-61496 parts 1 & 2 (Type 4)
- The certification number
- The certifying body
This information should help you to determine if the light curtain you are looking to purchase is indeed up to standard with OSHA.
Deciding Which Type of Light Curtain Is Right for Your Machine
There are a lot of factors at play when deciding between safety light curtain types. To decide, you have to know what category your machine is. You have to know what level of protection you’re looking for (PAC or POC). You have to know what your price range is. And you have to know what risk level your machine poses.
This question of the risk level posed by your machine is unquestionably the single most important consideration. After all, the main goal of a light curtain is to keep those working with the machine safe and to keep the machine in good working order as well. This means that you need to assess what level of danger the machine in need of guarding poses, and decide what level of security measures are necessary precautions.
It’s important to perform a thorough assessment of the potential risk posed by each machine that needs to be guarded. There is no one-size-fits-all solution when it comes to guarding machinery. Even though it may sound like Type 2 light curtains are the lesser option, sometimes they’re all that’s necessary. There are other times when the added layers of security in a Type 4 light curtain are necessary and nothing else will do. Every machine needs to be looked at carefully on its own to decide what is best suited for it.
One way to do this is to break down your assessment into three areas of examination that can be posed as three separate questions.
- How often are people exposed to this machine?
- How likely is an injury to occur?
- How severe is that potential injury likely to be?
When answering these questions, it’s always better to err on the side of overestimating. If you’re going to make a mistake, make the mistake of being over-prepared and taking more precautions than is necessary. The safety of individuals working with the machines is too important to risk.
A simple test that might help decide this question is to ask yourself when considering a piece of machinery: “Would I hesitate to put my hand in this area? Would I hesitate to be near this machine?” If you answer yes to either of those questions, then it’s probably the right decision to invest in a Type 4 light curtain. The potential for injury isn’t worth the risk.
How might this look when applied? Let’s say the machine you’re looking to protect is a conveyor. What is the worst injury that could occur from interacting with it? If you ask yourself if you feel comfortable putting your hand near the conveyor and the answer is not without some protection, you might want to consider a level 2 light curtain.
Consider a second example. Imagine you want to guard a pneumatic press that workers are closely interacting with all day long. The potential for injury here is much greater. Don’t take the chance of only taking a few safety measures. A Type 4 light curtain needs to be installed.
Consider whether you’re going to require POC or PAC protection. If you’re looking for something as finely detailed as finger protection, your options are limited to Type 4 light curtains. However, if you need only hand or body protection, either Type 2 or Type 4 offer this option.
Consider GES Repair for Safety Sensors
One of the most important aspects of your light curtains, Type 2 or Type 4, is making sure that they are in top working condition. If something has gone awry with your light curtains, the safety protocols won’t be working properly and your machines could be in danger of breaking down. The individuals working with the machines could be in danger of being injured.
It’s important not to wait. If your light curtains are damaged, or even if they just need to be checked for potential damage, don’t wait until it’s too late. Get your light curtains serviced before they become a problem and a danger to those around them.
If you’re looking to repair or service your light curtain, consider contacting GES Repair. Our technicians are relied upon every day by experts for help in servicing light curtains. Not only will we repair any damage to your light scanner, but we’ll also run a complete test before we return your equipment to you to ensure that everything is in correct working order. Give us a call today at 877-249-1701.