In brief
A safety light curtain is an electro-sensitive protective device that safeguards a hazardous area with parallel light beams.
Contents
What is Safety light curtain?
A safety light curtain consists of a transmitter and a receiver, between which a field of infrared beams is created. If a beam is interrupted, the safety outputs switch off and the hazardous movement is stopped. Light curtains replace fixed guards where material is frequently loaded or removed, for example on presses, packaging machines or palletisers.
The most important rating is the resolution: fine resolutions are used for finger or hand protection, coarser ones for body protection; multi-beam safety light barriers safeguard access points. Further characteristics are protective field height, range, response time, type to IEC 61496 and functions such as muting or blanking. The required safety distance to the danger point is calculated to EN ISO 13855 from the response time, the machine’s stopping time and the resolution. Muting temporarily bridges the protective field so that material can pass while people continue to be detected; blanking deliberately masks individual beams, for example for fixed machine parts in the protective field.
Typical causes of failure are mechanical damage, dirty front screens, misalignment and defective connecting cables. Because resolution and response time feed directly into the safety distance, a light curtain may only be replaced by a device with equivalent ratings.
In practice: maintenance and procurement
For a replacement, the manufacturer part number, protective field height, resolution, range, response time, type and connection type are needed, as well as details of muting or blanking. If an alternative device differs in response time, the safety distance must be checked again.
Synonyms and abbreviations: light curtain · safety light grid · ESPE · AOPD (active opto-electronic protective device)
Frequently asked questions
What is the difference between a light curtain and a photoelectric sensor?
A simple photoelectric sensor works with a single beam and is mostly used for object detection in the process. A safety light curtain creates many parallel beams, monitors itself and is approved as a protective device for people. Only devices designed as safety components may be used for personal protection.
How is the safety distance of a light curtain calculated?
The basis is EN ISO 13855. In simplified terms, the distance results from the approach speed of a person multiplied by the total stopping time, i.e. the response time of the light curtain and evaluation unit plus the stopping time of the machine, plus an allowance that depends on the resolution. The exact formulae and values are to be taken from the text of the standard.
What information is needed to replace a safety light curtain?
The manufacturer part numbers of transmitter and receiver, protective field height, resolution, range, response time, type to IEC 61496, connector type and activated additional functions such as muting or blanking are needed. With these data, it can be checked whether a replacement device maintains the existing safety distance.