Hermetic Contact
Hermetic Contact
(in Russian, gerkon), a hermetically sealed switch with spring contacts made of ferromagnetic materials that touch when acted upon by a magnetic field. A distinction is made among types that operate to close, transfer, or open electrical circuits. Inside the shell, which is not over 6.25 mm in diameter and 50 mm in length, there is either a vacuum or a gaseous medium (nitrogen, argon, or hydrogen) under various pressures. At a certain magnetic field intensity of an electromagnet or a permanent magnet, the free ends of the spring (most often made of permalloy wire), which are separated by several tenths or hundredths of a millimeter, are attracted toward each other and make contact. When the intensity is reduced, the elastic force of the springs returns them to the initial position, and the contact is opened. The maximum power that can be switched by the contacts is 4-60 watts. The resistance of a hermetic contact in switching circuits is 0.02-0.2 ohms when closed and 109-1015 ohms when open. Most of the gas-filled types have a breakdown voltage of 200-500 volts (V). By raising the gas pressure to several tenths of a meganewton per sq m (MN/m2), or several atmospheres, or by lowering it to 132 × (10−4 to 10−6) N/m2 (10−4 to 10−6 mm Hg) the breakdown voltage is increased to 800 V. In vacuum hermetic contacts it reaches 5,000 V.
A hermetic contact can withstand 108-109 operations. The operation time (0.5-2 millisec) and release time (0.1-0.7 millisec) are much shorter than in armature-type electromagnetic relays. A hermetic contact’s features include simple construction, reliability of operation, absence of adjustments, operation in any position over a temperature range from -100° to 200° C, and the possibility of automation of its manufacture. Hermetic contacts are used in telephone communications (as relays, switches, and so on) and in computer technology (as logic, summing, and encoding elements).