what is a difference between safety type-2 and safety type-4 of safety light curtains

The type 2 safety light curtains test their internal circuits periodically (every 500 ms for XUSL2E). If a failure appears between the two test sequences, it will be detected only after the next test.
The design of these light curtains is suitable for applications where the analysis demonstrates  a minor injury risk for operators.

• Type 2 is Less expensive than Type 4
• Type 2 is available only for hand and body detection

Type-4 safety light curtains
The type 4 design is based on redundant automatic cross-checking architecture. This architecture enables immediate failure detection within the response time.
The type 4 light curtains are suitable for applications where the analysis demonstrates a moderate or high injury risk for operators.

• Type 4 is available for finger, hand, and body detection
• Type 4 provides a shorter response time and narrower aperture angle (+- 2,5° for type 4 and +- 5° for type 2).

Released for:Schneider Electric India