PURPOSE: To enable the measurement of vacuum pressure of 102W1-5Torr, by providing a driving means of a vibration body and a means of detecting the position thereof on a vibration plate of tuning fork type vibrator comprising a parallel flat plates vibrating in the normal direction of a plate surface.
CONSTITUTION: Electrodes 43W45 provided on vibrators 41 and 42 of a tuning fork type vibration element are each kept electrically insulated through a base section 46 and the electrode 43 is earthed. When a voltage from a trigger circuit 51 is applied to a driving electrode 45 via a switch circuit 52 and an amplifier 53, vibrators 42 and 41 vibrates. With a constant voltage VCC applied to a detection electrode 44, an electrostatic capacitance at a gap 47 varies with the vibration of the vibrators 41 and 42 to generate a voltage corresponding to the amplitude. This voltage is made coincide in phase with a driving signal from a phase phase detection circuit 57 by a phase shift circuit 55 via an amplifier 54 and applied to the electrode 45 via circuits 52 and 53 to make a vibrator resonant. An output of an addition circuit 58 is displayed as vacuum pressure value by an amplifier 60 and a display conversion circuit 59.
SATO KAZUO
TERASAWA TSUNEO
TANAKA SHINJI
