It is known that N2 gas may be used for the water-proof test of wrist watches. This water-proof testing device for wrist watches can do without water for airtight examination. Compressed air is mainly applied except for the watch shops in shopping areas where N2 is used instead to avoid noises. Hamron Tec (President: Akihiko Aihara) is enjoying lion’s share in this field with the “WPC Series” (waterproof checker) which was launched for sale in 1975 and highly reputed for its easy recognition of waterproof effects. More than 6000 units have so far been sold and employed by all domestic watch manufacturers as a standard model actually.

The biggest feature of the product is in its employment of the “Strain Detecting System” to
examine sealing conditions by checking any distortion of the surface which is affected when pressure is loaded to such objects as wrist watch or smartphone. In case of wrist watches, if there is nothing abnormal in their waterproof properties, the glass surface gets a little strained. On the other hand, if there is something wrong like leakage in the waterproof property, high pressure gas (air or N2) gets into the watch to gradually remove the strain. It means that no distortion occurs despite application of pressure. Practically, a watch is placed on a sealed container and a strain detecting sensor is made in contact with the glass surface. Under the condition high-pressure gas is filled in to detect a strain in the micron unit. It is the glass body that is distorted, especially rubber or plastic materials used for the O-ring.

To cause strains to objects for testing, the specified pressure is applied at 0.3 to 0.5MPa for common wrist watches, 1MPa for diver’s watches of 100m waterproof and 2MPa of 200MPa and 10 kPa for a water proof level equivalent to IPX 7 like smartphone, tablet or wearable terminals. According to the staff in charge of the company, the demand for test equipment arose in 1970 when Citizen, Casio and Seiko started to produce waterproof-type wrist watches. The detector came up to the mainstream because it required less labor and cost than the conventional differential pressure system. Nowadays, the demand is spreading so wide as to waterproof testing of various terminals like smartphone and medical equipment including portable electrocardiograph or injector.

For waterproof testing in production plants, a 100% inspection is done using inexpensive compressed air, while N2 gas is used in ordinary shops where water proof testing service is provided at the time to change battery in many cases. The staff said, “Frankly speaking we have no idea of how much percentage of N2 is consumed. But we have heard a certain watch shop consumes one cylinder per one or two months.”