A New Hot-Wire Vacuum Gauge

Abstract

IT is known that the range of a hot-wire vacuum gauge may be extended to 10 mm. mercury pressure or above, if by some means the current supplied to the wire is increased with increasing pressure^1,2. Attempts have been made to do this with the aid of automatic devices. Such a gauge becomes easier to handle, and there is then no danger of overloading. One of these circuits (suggested in principle by Mr. G. von Dardel) (Fig. 1) consists of an amplifier tuned on 800 c.p.s. A regenerative feed-back is provided by a bridge containing the hot wire. The amplitude of oscillations adjusts itself to keep the temperature of the wire approximately constant at all pressures. The amplitude is read by a diode circuit. Two ranges of sensitivity are provided. The output meter is protected from dangerous overloading by a rectifier which, however, distorts the readings slightly.