Type 4 Safety 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 will not resume operation until the affected parts have been inspected and possibly replaced and the system reset

          Type 2 safety light curtains regularly test their internal circuits and do not perform tests between two test sequences.If there is a problem, it will only be detected in the next test which means that Type 2 safety light curtains are only suitable for situations where the risk level is acceptable

          In general,type 4 safety light curtain can be considered  as upgraded type 2 safety light curtain-in general,type 4 safety light curtain can be considered as upgraded type 2 safety light curtain-more expensive,safer,more reliable