What are the solutions for false alarms of safety light curtains?

In the automated production line, the safety light curtain is an invisible “lifeline”. It relies on infrared to detect intrusion and achieve non-contact protection. Once a person or object blocks the light beam, the system will trigger a shutdown and alarm to protect the operator’s personal safety.

However, in actual applications, many companies often encounter a thorny problem: the light curtain is not blocked, but it frequently falsely alarms, resulting in frequent equipment shutdowns and a serious decline in production efficiency.

This situation confuses many people: Is the light curtain broken? What is the problem? How to deal with it?

Today, let’s talk about the 5 common causes of false alarms of safety light curtains and the corresponding solutions. This article will help you solve the problem of “neurosis” of light curtains.

1. Environmental interference: sunlight, welding light, and reflections are all “invisible killers”
   Phenomenon:
   When the equipment is close to a window or a strong light source, the safety light curtain suddenly alarms, even if there is no one around.

Cause analysis:
The infrared light curtain uses infrared rays in the 850nm~950nm band, and sunlight, welding arc light, and strong reflected light also contain strong interference light in the same band, which can easily cause the light curtain receiver to “misjudge as blocked”.

Solution:
Add a sunshade or protective plate to the light curtain to avoid direct sunlight;
Try to avoid windows or highly reflective metal surfaces when installing;
Use industrial-grade safety light curtains with anti-strong light interference function, and it is recommended to choose models with an anti-interference level of >10,000Lux.

2. Dust and oil mist: The sensor “cannot see clearly” and naturally alarms randomly
   Phenomenon:
   After the equipment has been running for a period of time, it begins to frequently report false alarms, and it returns to normal after wiping it.

Cause analysis:
The lenses of the light curtain transmitter and receiver are covered with dust, oil mist, and dust, resulting in the inability to transmit or receive infrared beams normally.

Solution:
Clean the transmitting and receiving lenses of the light curtain regularly, it is recommended to do so once a week;
Install a transparent protective cover in workshops with high oil smoke and high dust;
If the environment is too harsh, it is recommended to choose a light curtain product with a protection level of IP65 or above.

3. Misalignment during installation: The optical axis is biased, and the signal is naturally unstable
   Phenomenon:
   It keeps alarming as soon as it is installed. It can be used again after adjusting the angle, but it will not work again after a while.

Cause analysis:
The safety light curtain is a one-to-one transmission and reception relationship. If the optical axis is not strictly aligned during installation, some light beams will “not receive signals”, resulting in false alarms.

Solution:
Use the alignment indicator or laser alignment tool provided by the manufacturer to ensure that each beam of light is aligned;
Use a stable bracket to fix the light curtain to avoid displacement caused by equipment vibration;
For long-distance applications, select an intelligent light curtain with automatic alignment prompt function.

4. Electromagnetic interference: The signal line is polluted by “noise”
   Phenomenon:
   Frequent false alarms during certain periods, especially when high-power equipment is about to start.

Cause analysis:
The signal line or power line of the light curtain is wired close to strong electricity, high-frequency motors, inverters, etc., which is susceptible to electromagnetic interference and “false signals”.

Solution:
The signal line and the strong wire are routed separately, and the distance is more than 10cm;
Use shielded cable to connect the light curtain and ensure grounding;
All control boxes, power supplies and PLC systems are well grounded to prevent voltage floating.

V. Program or logic setting error: software problems cause misjudgment
Phenomenon:
The light curtain is not blocked, but the equipment alarms, and it returns to normal after restart, which is very sporadic.

Cause analysis:
Some equipment systems use PLC or safety controller to process light curtain signals. If the logic programming is not rigorous or the settings conflict, it may also cause false alarms.

Solution:
Check the judgment logic of the light curtain input signal in the PLC program to see if an overly sensitive trigger condition is set;
Check whether the light curtain response delay setting (such as delay time, hold time) is too short;
Check whether the emergency stop and linkage modules associated with the light curtain are set to “default high level input” and misidentify the “interrupt” state.
Additional suggestions: Establish a fault record and regular inspection mechanism
Don’t wait until the light curtain “completely fails” before dealing with it. Many false alarm problems have small signals and small abnormalities in the early stage. As long as regular inspections are carried out, hidden dangers can be discovered in advance.

It is recommended to conduct a complete test of the light curtain once a month, including occlusion detection, signal response, and logical linkage, and keep records and archive them so that they can be quickly traced once an abnormality occurs.