Self-checking guard switches reduce machine downtime

Paul Boughton
An innovative position switch for machine guards from the Siemens Industry Automation Division is said to offer a number of practical advantages. In addition to fulfilling the Asisafe standard, the Sirius 3SF1324 position switch also fulfils the demands of safety integrity level 2 (SIL 2) and Performance Level d (PL d). Moreover, the operator receives a checkback signal from the magnet and no longer has to open the protective doors each time after magnet release in order to set machinery or plant to a safe state again. This feature enables the machine to be restarted more quickly after door release.
This new position switch with tumbler and Asisafe communications is available in three versions: with auxiliary release at the front, with escape release at the front, and with both auxiliary release at the front and escape release at the rear.
Sirius 3SF1324 switches are said to be especially advantageous when connected in series or when several guards are to be controlled as a group. It is no longer necessary to open and close each door individually in order to establish the safe state. This both reduces downtime and ensures that the machine or plant resumes operation much quicker. The engineers at Siemens have developed a special logic for the new position switches: the double evaluation of the actuator required for safety category SIL 2 / PL d now takes place within the switch. This information is then reported safely to the control system via one of the two Asisafe transmission channels, while the second channel is simultaneously used for the operating status signals or status query of the door interlock magnets.
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