Safety light curtains: the need for inspections
March 1st 2008

Companies using light curtains to safeguard machinery often do not appreciate the implications of the regulatory requirement for inspections. Steward Robinson of Pilz Automation Technology explains the requirements.

While safety light curtains may appear to be fit-and-forget devices, most suppliers state that they should be inspected regularly. In this context, 'regularly' is normally interpreted as 'annually'.

Electrosensitive protective equipment certification involves an inspection to ensure that the light curtain cannot be defeated and that it is correctly positioned in relation to the mechanical hazards. Note that sometimes people refer to Active Optoelectronic Protective Device certification, which is the same as ESPE certification.

A typical machine with a single safety light curtain would take about 1h to inspect and a little more time to complete the documentation. Information on the requirements for ESPE assessments are contained in IEC 62046 (Technical Specification, Safety of machinery - Application of protective equipment to detect the presence of persons).

The height of the hazard window is checked, together with the size of the light guard and its type, to ensure the guard adequately covers the hazard window. A stop time performance monitor is mounted on the machine to measure how long it takes for moving parts to come to a standstill from the moment the light barrier is triggered. This figure is used to calculate the required distance between hazard and light guard as per BS EN 999:1999.

The actual distance is measured so that it can be compared with the calculated figure to ensure the light guard is mounted in the correct position.

The guard is then checked to ensure it is correctly integrated within a suitable safety-related control system.

A written report is then prepared for every machine inspected.

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