Type 2 vs. Type 4 Light Curtains Explained: Choosing the Right Protection Level
When upgrading machine safety, one of the most critical decisions engineers face is selecting the correct safety light curtain. According to international safety standards (IEC 61496-1/-2), safety light curtains are primarily classified into two categories: Type 2 and Type 4. Choosing the wrong type can either lead to dangerous compliance failures or unnecessary overspending.
How Does a Safety Light Curtain Work?
In this article, we will explain the technical differences between Type 2 and Type 4 light curtains, using DAIDISIKE's MK/JER Series and DQT4 Series as practical industrial examples.
I. What is a Type 2 Safety Light Curtain?
Type 2 safety light curtains are designed for applications with a lower risk of severe injury. According to ISO 13849-1, they typically correspond to Performance Level c (PL c) or Safety Integrity Level 1 (SIL 1).
- Fault Detection: Type 2 light curtains periodically perform self-checks. If a fault occurs between the test intervals, the machine might not stop immediately until the next check detects the error.
- Cost-Effective: They use less complex internal circuitry, making them a highly economical choice for lower-risk automated zones.
The DAIDISIKE MK Series and JER Series are excellent examples of high-quality Type 2 light curtains. A standout feature of these series is their Optical Synchronization technology. Because they synchronize via light beams rather than a physical CP (control) wire, the wiring process is incredibly simplified, reducing installation time. They are widely used in automated assembly lines, packaging machines, and low-risk testing stations.
II. What is a Type 4 Safety Light Curtain?
Type 4 safety light curtains offer the highest level of protection. They are mandatory for machines that pose a high risk of severe, irreversible injuries (such as amputation or death). They correspond to Performance Level e (PL e) or Safety Integrity Level 3 (SIL 3).
- Continuous Self-Checking: Type 4 devices monitor themselves continuously in real-time. If a single electronic component fails, the system immediately issues a stop command and enters a safe lockout state.
- Redundancy: They feature dual-channel architecture. Both channels must function correctly for the machine to operate, ensuring zero margin for error.
The DAIDISIKE DQT4 Series is engineered for extreme high-risk environments. Built with rigorous internal redundancy and continuous diagnostic capabilities, the DQT4 series is the standard choice for heavy hydraulic presses, metal stamping machines, and robotic welding cells where operator safety cannot be compromised.
III. Head-to-Head Comparison: Type 2 vs. Type 4
To help you make a quick and accurate purchasing decision, here is a technical comparison table between our Type 2 and Type 4 offerings:
| Specification | Type 2 (MK & JER Series) | Type 4 (DQT4 Series) |
|---|---|---|
| Safety Level (EN ISO 13849) | PL c / SIL 1 | PL e / SIL 3 |
| Fault Detection | Periodic self-testing | Continuous real-time self-checking |
| Synchronization Method | Optical Synchronization (No sync wire needed, easy wiring) | Wired / High-speed electronic synchronization |
| Internal Redundancy | Single fault may not trigger immediate stop | Dual-channel redundancy; safe lockout upon any fault |
| Typical Applications | Packaging, light assembly, automated guided vehicles (AGVs) | Hydraulic presses, stamping, robotic cells, heavy machinery |
IV. How to Choose the Right Light Curtain?
The choice between Type 2 and Type 4 always begins with a formal Risk Assessment. If an accident could result in a minor injury (e.g., a bruise or small cut) and the frequency of exposure is low, a Type 2 optical-sync sensor like the MK/JER Series is the most efficient choice.
However, if an operator interacts with a machine multiple times an hour (like a punch press) and the potential injury is severe, international safety regulations mandate a Type 4 sensor like the DQT4 Series.
V. Conclusion
Understanding the difference between Type 2 and Type 4 light curtains ensures your factory remains both compliant and cost-efficient. DAIDISIKE (戴迪斯科) provides a full spectrum of safety solutions tailored to your specific risk assessment results.
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