Dallas T. Hurd

A Recording Vacuum Gauge

The Langmuir viscosity vacuum gauge has been modified to provide electrical recording of low‐pressure data. A particular advantage of this type of gauge is that, once calibrated, it may be used with any gas, including reactive or unstable compounds, or with gases having low condensation pressures.The gauge utilizes the changing capacitance between a stationary electrode and an oscillating fiber, the rate of damping of which is a function of the composition and pressure of the ambient gas, to modulate the frequency of an oscillator. The output from the oscillator is demodulated in a discriminator circuit, amplified, and recorded. The pressure of the gas is then determined from the recorder trace. Alternatively, the signal may be used to actuate relays or servomechanisms. The fiber is set into oscillation by means of an electromagnet, so the entire operation of the device may be made automatic if desired.