When the young telecom engineer Nils Palmgren was taking a walk one evening in the early 1910s, he suddenly had a vision of how ten incoming telephone lines in a telephone exchange could be placed in contact with 100 outgoing lines. Upon returning home, he made a sketch of what he had seen. The sketch was of historical importance, since it resulted in the link principle for how it is possible to connect to and maximally utilize all available outgoing lines. This principle would subsequently be used in the crossbar switching system and later in electronic systems.
Palmgren was just over 20 when he was employed by the development company AB Autotelefon Betulander. Palmgrens boss, Gotthilf Ansgarius Betulander, believed that an automatic telephone system should be as simple as possible and based on the telephone relay. It was during work on relay systems that the ingenious link principle was developed. The principle was patented in 1912 by Palmgren and Betulander.
During work on a test installation, the idea for a crossbar switch was born. Betulander and Palmgren applied for a patent in 1919 for a switch with horizontal and vertical arms that directly controlled a fixed group of relay springs at the intersection point. The first large crossbar switching station was manufactured by Televerket, the Swedish PTT, and put into operation in Sundsvall in 1926. When the Swedish telephone system was automated, the crossbar switching system was used in parallel with Ericsson's 500-switch system.
Autotelefon Betulander ceased operations in December 1919, and Palmgren was employed by Ericsson, where he worked until his retirement at posts that included manager for the telephone station laboratory.
Palmgren received several awards for his contributions, including Ericsson's bronze award in 1941 and the gold medal in 1946. In 1950, he was awarded the gold medal by the Swedish Engineering Society and five years later the silver award, the highest distinction within Ericsson. Nils Palmgren was a quiet person who found it easy to work with others. His shyness made him reluctant to talk about his own contributions. He died in January 1975 at the age of 75.
Author: K V Tahvanainen
