Riefler Escapement - Riefler Clocks

Riefler Clocks

Clemens Riefler precision regulator clocks achieved accuracies of 10 milliseconds per day. and were guaranteed to be within 30 milliseconds. With over 600 made, they were one of the most widely used astronomical regulators, and became the highest standard for timekeeping in the early 20th century. They were used worldwide in astronomical observatories, naval observatories, and as primary standards for electrical time dissemination services, which delivered time signals by telegraph wire. Riefler clocks had internal switch contacts for this purpose, which delivered a 1 Hz time signal to external equipment. The first time standard for the United States, provided by the Bureau of Standards (now NIST), was from 1904 to 1929 generated by Riefler clocks.

In addition to the Riefler escapement, Riefler clocks' mechanism had several other innovations which were responsible for their accuracy. They were one of the first clocks to use a pendulum rod made of the low thermal expansion alloy invar, to prevent the pendulum from changing length with temperature changes, causing error. The most accurate models were mounted in a low pressure tank to eliminate the effect of changes in atmospheric pressure on the pendulum. They were powered by a gravity remontoire, a small weight which was wound up by an electric motor every 30 seconds, to eliminate the effect of changes in drive force on the mechanism.

Working Riefler precision pendulum clocks on display to the public are located in the lobby of Olin Hall at Carleton College in Northfield, MN, the Deutsches Museum in Munich, the National Watch and Clock Museum in Columbia PA, the Musée international d'horlogerie in La Chaux-de-Fonds, the Musée d'horlogerie in Le Locle, the Deutsches Uhrenmuseum in Furtwangen, and at the US Naval Observatory (by appointment only) in Washington DC.