Journal of the Horological Institute of Japan

A simple, low-cost "level sensor" has been developed. This sensor detects three inclination states of examined plane i. e. right-upward, horizontal and left-upward. A fan-shaped pendulum detects the direction of gravity. Inclination angle of ezamined plane relative to the pendulum is converted to voltage by photointerrupters. Then, voltage comparators make digital output signals which indicate the inclination states. When the pendulum is moving, a magnetic damper composed of a pair of permanent magnets causes eddy current and gives the proper response time to the pendulum. As one of applications, we examine attitude control of an agricultural tractor. Using a simplified model, range of damping constant in which the tractor works normally is calculated. Experimental values agree well with the culculated results.

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Among diver's watches, those for professional divers have pressure-resistance against depth which have become deeper as 300m, 500m, 600m, 1,000m, and 2,000m. It is known, however, that helium gas penetrates into the watch and Increases the inner pressure during the deep-sea diving. Further, such trouble as the crystals get out from place in decompression, as the inner pressure of the watches becomes higher than the environmental pressure. In order to investigate these problems, the variation of inner pressure of watches was measured by special pressure gauges connected to watch cases through the crown fitting holes of four types of typical deep-sea diver's watch (for 300m, 600m, 610m, and 1,300m) in the 300m saturation diving experiment (SEADRAGON-V). As the result, inner pressure of 0.7 kg/cm^2 was observed in the watch case of two-piece struCture, and 2.4 and 3.4 kg/cm^2 in two watch cases of three-piece structure respectively. In all of these cases, O-ring of butyl rubber were used to avoid penetration of helium gas. While, the highest value of 5.3 kg/cm^2 was observed in the watch case using O-ring of neo-prene. In the watch case equipped with an exhaust valve of non-return type, the inner gas was discharged with a reduced pressure in decompression during which the inner gas pressure remained not higher than the environmental pressure. While, in the watch case with O-ring of butyl rubber, the reduction of inner pressure was extremely so slow that it took nearly 300 days to return to the atmosphric pressure. This fact suggests a new problem. From the above result obtained by diving during four days, it may be estimated that inner pressure of an ordinary deep-sea diver's watch with O-ring of neoprene would rise up to around 15 kg/cm^2 during the saturation diving of 300m for 15 days, and the danger of the crystal getting out from place would increase cons iderably in decompression. It is considered, therefore, that the helium-resistance. test is indispensable for deep-sea diver's watches.

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