EN81-20 Detectors

In August 2014 two new standards covering lift design (EN 81-20:2014) and installation requirements (EN 81-50:2014) were released in Europe. These replace EN 81-1:1998+A3:2009 and EN 81-2:1998+A3:2009, which were 15 years old and needed upgrading to comply with modern safety requirements. It is expected that the new standards will also be adopted in China, South America and Australia.

Many factors have influenced the creation of these new standards, such as:

• Improvements in safety due to changes in proven technology and the need to reflect changes to the state of the art;
• The incorporation of essential health and safety;
• Requirements from modified EU Directives;
• The elimination of reported errors;
• The clarification of the text and the incorporation of proposals resulting from interpretation requests.
•  There are no longer separate standards for hydraulic lifts. Risk analysis and compliance with the essential requirements of the Lift Directive are key.

Examples of new requirements are:

• Increased strength of doors, car and well;
• Increased lighting in the lift car;
• The need to prevent people leaving the car if it is stopped between floors;
• Improved materials used in the car enclosure (flameproof materials and safety glass);
• Better classification of loading conditions and safety using loading vehicles (forklifts etc.);
• Increased refuge space in the pit and headroom;
• A pit control station and improved car top control;
• Improved pit access (ladders, control positions, etc.)
• Emergency lighting on the car roof;
• An improved balustrade on the car roof;
• A door-bypass control to prevent the deliberate bypassing of safety circuits (using “shorts”).

Both new and old standards will be valid during the current 36-month transitional phase, but from August 2017 EN 81-1 and EN 81-2 will no longer apply.

How does EN 81-20 affect lift door detectors?

The specific part of the standard relating to lift door detectors is covered in section 5.3.6.2.1.1 of EN 81-20:

5.3.6.2.1.1 Automatic power operated doors

The following applies:

1. a) The kinetic energy of the landing and / or car door and the mechanical elements which are rigidly connected to it, calculated or measured at the average closing speed shall not exceed 10J.

The average closing speed of a sliding door is calculated over its whole travel, less:

1) 25mm at each end of the travel in the case of centrally-closing doors;

2) 50mm at each end of the travel in the case of side-closing doors;

1. b) A protective device shall automatically initiate reopening of the door(s) in the event of a person crossing the entrance during the closing movement. The protective device may be rendered inoperative in the last 20mm of door closing or gap;

1)The protective device (e.g. light curtain) shall cover the opening over the distance between at least 25mm and 1600mm above the car door sill;

The maximum detection height has been reduced from 1800mm to 1600mm.

2)The protective device shall be capable of detecting obstacles minimum of 50mm diameter;

Manufacturers of light curtains now have to guarantee that their detectors can detect objects with a diameter of at least 50mm. This has a significant impact on the number of diodes used in a traditional light curtains. Avire has developed unique test equipment that can automatically plot the protection coverage of a light curtain. Figure 1 was plotted using a 50mm object that was scanned vertically 18 times between the two detectors mounted at 1000mm separation. The continuous red vertical line indicates a trigger. Gaps in the vertical line indicate no trigger. As can be observed in figure 1, the spacing of an 18-diode detector is not sufficient to ensure 100% detection coverage with a 50mm object at the detector edge. The diagonals beams used within Avire detectors effectively fill in the pattern away from the edge.

It is easier to see the impact of the diagonals on detection capability by reducing the test object to something much smaller e.g. 15mm – Figure 2.

The standard way to resolve this issue with poor coverage at the surface of the detectors is to increase the diode count so that the inter-diode spacing is less than 50mm, as can be seen from Figure 3.

3) To counteract persistent obstructions when closing the door, the protective device may be deactivated after a predetermined time;

This could be due to a physical obstruction or vandalism e.g. chewing gum on the detectors.

4) 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.

This implies that when the light curtain detects a fault condition this should be conveyed to the door controller to limit the closing force of the doors. The failure of the light curtain can be communicated in many different ways from the most simple, where the door controller identifies a permanent trigger of the detector diagnostic output, to more sophisticated diagnostic protocols. The implication, if the diagnostic output is a simple form of relay, is that it should be configured as “normally closed” to ensure that the system fails safe if the detector, wiring or power supply is compromised. Alternative solutions include protocols such as CANopen and customer-specific protocols based on the RS485 physical layer. It is also important to note that during the fault condition an alarm (acoustic signal) should also sound when the doors are closing to warn pedestrians.

Conclusion

It is important to start discussions now with a supplier of light curtains that has a good understanding of the new European regulations and can offer a variety of solutions to meet your system needs. When companies are evaluating options to meet the new guidelines, Avire will assist with the selection of the most cost-effective method.