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The EN81-20 standard is related to the safety rules for the construction and installation of lifts for the transport of persons and goods.

Clauses which directly impact light curtains

• The protective device (e.g. light curtain) shall cover the opening over the distance between at least 25 mm and 1600 mm above the car door sill
• The protective device shall be capable of detecting obstacles minimum of 50 mm diameter – 37mm diode spacing
• In case of failure, or deactivation of the protective device, the kinetic energy of the doors shall be limited to 4J, if the lift is kept in operation, and an acoustic signal shall operate at any time the door(s) is (are) closing. – Diagnostic output

Ingress protection, used to define levels of sealing effectiveness of electrical enclosures against intrusion such as dust and water.

Each light curtain set contains a Transmitting edge (TX) and a Receiving edge (RX). The TX contains an array of Infrared LEDs which illuminate in sequence, and the RX contains a corresponding array of photoelectric diodes tuned to the LEDs' frequency. These receive light in sequence generating either a parallel or a diagonal beam pattern.

When an object blocks one of the beams, the RX sends a trigger signal to the door controller, and the doors reopen.

Avire’s light curtains are designed to minimise the potential interference from sunlight. Infrared radiation from any source of light may interfere with the receiving diodes, and this normally sets the maximum limit to the operating range of the light curtain. In installations where the door width is outside the specified range and where there are many sources of light, including sunlight, light curtain performance may deteriorate over time.

In multi-door lifts, we advise that installers arrange the two detector sets in such a way to minimise the potential for crosstalk. In cases when the doors are adjacent to one another, install the two Transmitter (TX) edges at the same corner of the lift. In cases where the doors are on opposite sides of the lift, install the two TX edges at diagonally opposite corners of the lift.

This is a second, independent output that works in parallel to the detector trigger output. Under EN81-20 standards, a 50mm object must be detected within the detection zone at all times – any breach of this must result in the doors going into a low energy mode if the lift is to remain in use. A blocked or damaged diode may create a gap within which a 50mm object will not be detected. If a diode is broken, this could result in non-compliance.

Rather than allowing a single diode blockage to cause a permanent trigger, the diagnostic output can trigger the door’s low energy mode and put the blocked diode in timeout mode. The remaining diodes can operate as normal, the lift can continue to be used, and the detection remains EN81-20 compliant.

Avire detectors are designed to account for some misalignment between the detector pairs. This is both angular and lateral. It is always advised, however, that the two edges are aligned as well as possible during installation to maximise the system’s sensitivity.