Heidenhain EncodersThe international ALMA project is a source of prestige for all those involved. Although the observatory is to be completed in 2013, it was already supplying breathtaking images from the depths of the universe on October 3, 2011.

25 of 66 antennas are from Europe, and equipped with HEIDENHAIN angle encoders. It is this alone that makes precise positioning of the antennas possible. With each antenna weighing several tons, the angle encoders provide the precision needed for the next-generation astronomical observations.

Atacama Large Millimeter/submillimeter Array (ALMA)

The ALMA observatory in the Atacama Desert in northern Chile is the most powerful radio telescope in the world, and the world’s most complex terrestrial observatory. With ALMA – short for Atacama Large Millimeter/Submillimeter Array – astronomers aim to investigate remote galaxies and search for the building blocks of solar systems and inhabitable planets. Construction of the observatory is not yet complete, yet the unexpectedly high level of precision has caused furor throughout the world.

Until now around a third of the 66 radio antennas planned have been set up on the desert plateau at a height of 5,000 metres. ALMA does not use one single antenna to observe the cosmos but several receivers positioned precisely and interconnected to become a single telescope. Alma Correlator, one of the most rapid specialised supercomputers in the world, calculates the image data of the antennas to produce a general overall view

Pinpoint accuracy, light years away

The coupling of the antennas to produce a giant telescope enables ALMA to capture images of celestial bodies at a distance of many millions of light years. Exact positioning of the antennas weighing several tons is of elementary importance, and the slightest imprecision distorts the result and lead to blurred images. See more about how ALMA works.

A decision was taken by those responsible for the 25 European radio antennas to order angle encoders from Heidenhain. With outstanding measurement precision and a high level of long-term stability, these devices ensure the required accuracy for alignment of the ALMA antennas. A special strength of the Heidenhain angle encoders used in the project is outstanding precision within one signal period. They function without contact and are thus especially suitable for use in precision devices.

Precise measurement of horizontal and vertical angle.

To align the horizontal angle (azimuth) with precision, the European ALMA antennas use the new incremental ERA7480C angle encoder with 247,800 scale lines and a diameter of 3155 millimetres.

The ERA7480C was specifically developed for use with the ALMA and the tape length was adapted precisely according to the required diameter. Achievable precision was simulated beforehand as a part of project development. The ERA7000 angle encoders consist of a scanning unit and a one-piece steel scale tape as graduation carrier.

The vertical angle (elevation) is set by the researchers in Chile with the aid of the ERA4282C angle encoder from Heidenhain. The especially precise angle encoder of the ERA4000 series with steel scale drum has 32,786 scale lines and a diameter of 209 millimetres.

The interface electronics from Heidenhain adapt the encoder signals to the interface of the subsequent electronics. The new external EIB749 interface box interpolates and compensates the output signals from the scanning head, and position values are output via Ethernet to the antennas control computer.

LG Motion supply and utilise Heidenhain Angle Encoders in a range of bespoke solutions for customers through Europe and the Middle East.

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