To acquire theoretical knowledge for future work, Ehrhardt went to the Polytechnic Institute in Düsseldorf for three months, starting in November 1833.
That same year, preparations began for the construction of Le Belge, the first steam locomotive manufactured in Belgium.
The locomotive was completed in 1835 by Robert Stephenson and Company, for use on a planned railway from Brussels to Mechelen.
In 1836, Ehrhardt attended the Arts and Crafts School in Düsseldorf for further theoretical studies and to improve his skills in technical drawing.
He invented the two-sided brake with oscillatory waves in 1847, and the portable Ehrhardtsche scale to control axle loads in 1879.