Operating Principles, Common Questions, and Performance Data for an Atmospheric Driven Atmos Clock

The elegance of the Atmos clock and the curiosity of mankind in self-operational mechanical systems have propelled this time device into our collective desire for more knowledge. The search for a self-winding time piece, based on normal atmospheric fluctuations, was pursued for centuries by horologists with the well-known clock proposed by J. L. Reutter and commercialized by Jaeger LeCoultre. This clock has generated numerous discussions throughout the years as noted in past Bulletin articles and other correspondences within the time keeping community. In this paper, the operating principles of the Atmos clock will be reviewed using fundamental science and engineering principles. Next, key questions and experimental observations will be discussed in light of the operating concepts to clarify the clock’s performance. Finally, an extensive database will be introduced which was gathered through physical measurements and data recording of an Atmos 540 clock. Introduction The first commercially successful atmospheric driven clock was created and patented by Jean Leon Reutter in 1928 (France) and 1930 (Switzerland). The concept was later refined by Reutter and Jaeger LeCoultre and fully commercialized with Atmos clock production continuing today [1]. In the first design (1928-1938), two glass bulbs containing mercury and a small amount of ammonia were connected to form a U-tube. These fluids responded to atmospheric changes and changed the assembly’s center of gravity so that it pivoted back-and-forth to wind a flat spiral spring using a ratchet. In contrast, the second design (1938 to present) utilized ethyl chloride within a sealed bellows to wind the mainspring using a ratchet and linear displacement of the end plate. The Atmos clock represents a long effort to develop a time piece that requires no human interaction or electrical power source [2]. In 1740, Pierre de Rivaz demonstrated a clock that operated solely on variations of temperature and air pressure [3]. In essence, changes in atmospheric pressure cause mercury column height variations which may be converted into rotary motion for clock power. James Cox and John Merlin created a clock driven by barometric pressure changes in the Atmos Article for NAWCC Bulletin 2 1760s [4]. A wristwatch has been developed by Phillips [5] which uses a bimetallic coil which operates on temperature differences to wind the mainspring. A detailed history of the Atmos clock development process and manufactured products has been authored by Lebet [6]. In an on-line posting, Hubby [7] discussed the Atmos clock operation with both mercury filled U-tube and ethyl chloride charged bellows. The prototype Reutter clock design operated only on temperature variations due to the hermetically sealed and rigid container which did not experience significant pressure changes due to external barometer variations. The Horological Journal [8] offered an operational analysis of the U-tube configured Atmos clock with attention focused on power generation, gear train design, and temperature driven performance. In contrast the refined Atmos clock bellows were affected by both temperature and pressure variations, although the latter had a smaller effect [9]. Deith and Aked [10] offered an overview of the Atmos clock movement and temperature/barometric pressure motor. An Atmos Calibre 58 clock had been discussed by Monk [11-13] with a discussion of static and dynamic pendulum balancing, lubrication, and mechanical dismantling/reassembly. For many years, the NAWCC Bulletin had hosted discussions in “The Answer Box” championed by Henry Fried [14] and Paul Heffner [15] as well as “Vox Temporis” [16] regarding Atmos clock operation. Clearly, great interest remains in the fundamental operation of this thermodynamically driven mechanical time keeping mechanism. A detailed technical analysis of an Atmos 540 clock (refer to Figure 1) will be undertaken to address a number of poised questions over the past five decades. The article is organized as follows. First, the Atmos clock components will be identified with photographs and a physical database listed in Appendix A. The mechanical and thermodynamic operations will be discussed to establish a technical basis to understand the ethyl chloride properties, bellows motion, stored energy in the mainspring, motion works transmission of spring energy through the gears to the escapement, and torsional pendulum behavior. Second, analytical calculations and experimental measurements will be presented to support a detailed energy analysis of the clock’s performance. Some of the topics addressed regarding the clock include power usage, energy harvesting, effect of surrounding temperature and pressure variations, and elevation Atmos Article for NAWCC Bulletin 3 changes. Third, the conclusion offers some final thoughts on the innovative Atmos clock and the many efforts over several centuries to realize an atmospheric driven clock. A complete Nomenclature List is contained in Appendix B as the mathematical symbols may not be defined in the text. Figure 1: Atmos 540 in protective glass enclosure to minimize pendulum air currents, and enclosure removed with bellows container mounted on backside Atmos Clock Components and Mechanical / Thermodynamic Operation The Atmos 540 clock principal components are the energy harvesting bellows and mainspring, motion works, escapement, and torsional pendulum as listed in Table 1 and labeled in Figure 2 [17]. In brief, the two-piece bellows canister, housing the ethyl chloride filled bellows and stiff coiled return spring, attaches to the circular retainer on the back side of the rear support plate with a twisting motion. A winding chain, pinned to an end-cap supported by a soft coil winding spring, follows and transmits the contraction motion of the bellows to mainspring winding through a one way ratchet mechanism. Note that only chain displacement, no energy harvesting, occurs when the bellows expands since the chain winding drum spring maintains tension in the chain and the ratchet does not allow rotation in the opposite direction. The stored potential energy in the mainspring, contained within a barrel, drives the motion works in a manner similar to a pocket watch. A series of six arbors, featuring a number of wheels and pinions, Atmos Article for NAWCC Bulletin 4 Figure 2: Atmos 540 mechanism with bellows and dial removed for identification [20] reduce the torque and increase the angular rotations to drive the escape wheel. The escape wheel interfaces with the lever escapement which contains twin pallets and counterbalance. The end of the pallet Elinvar wire (12) (inside tube) Pallet fork (10) Impulse roller (11)