Page 9 - Brochure

TECHNICAL
Elevator Safety – continued
ELEVATOR SWITCHES
Oleo elevator bu ers are designed to withstand many more maximum load impacts than elevators are likely to experience in their service life. Despite this, elevator bu ers remain an emergency only device. It is never a desirable outcome in the real world to have to rely on bu ers to bring your elevator to a stop – that said, it is absolutely essential that you can rely on the bu ers in the event that they are required.
It is for this reason that many elevator bu ers are fitted with a switch. The switch is positioned to detect that the bu er is fully extended and therefore ready for impact in the case of an emergency. If for any reason the switch does not detect full bu er extension, the entire elevator system is shut down.
MODELLING AND ANALYSIS
Oleo employs computer modelling and analysis to refine elevator bu ers performance. Simulations are compared directly with test results obtained on Oleo’s own in-house dynamic test facility. The ability to both simulate and test, has allowed increased optimisation of elevator bu er performance, providing benefits in terms of cost, safety and reliability.
BUFFER TYPE TESTING
Elevator bu ers are subjected to a type test before they can be sold to the market. Type test requirements vary depending on country but most follow the guidelines of the European specification EN81-20 or ASME A17.1.
To comply with the requirements of EN81-20 the bu er must perform to the criteria detailed earlier. To establish this, the bu ers are subject to drop tests. This is where a mass is dropped in freefall. The drop tests must take place at a temperature between 15°C and 25°C. Tests are conducted with masses at either extreme of the stated mass range of the bu er. Subsequent to the maximum mass drop, the mass must remain on the bu er for a minimum of 5 minutes, after which the bu er must fully re-extend within a time period of 90 seconds. Measurements must be made of the displacement, velocity and acceleration of the freefalling masses at a sample rate of at least 100Hz.
In order to eliminate erroneous noise and high frequency vibration from accelerometer traces, low pass filtering is usually applied to a signal sampled at a higher than required sampling frequency.
PANORAMA OF THE NEW YORK CITY SKYLINE IN MANHATTAN
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