Use of capacitance diaphragm gauges at pressures down to 10−6 Torr

The useful range of a capacitance diaphragm gauge is extended down to 1×10−6 Torr with an uncertainty of ±10−7 Torr using computer-based averaging. Gauge linearity is measured by observing the deflection of the diaphragm by the force of gravity. Precise pressure increments are generated by tilting the gauge through a range of accurately measured angles. By this procedure the gauge is observed to be linear to within ±1% plus 10−7 Torr between 1×10−6 and 8×10−3 Torr. Additionally, the deflection of the center of the diaphragm per unit pressure is found to be 2×10−5 m Torr−1.