A Capacitive Gauge for the Accurate Measurement of High Pressures

A highly accurate and precise pressure gauge, which utilizes the 35°C, 2005 Hz dielectric constant of an ionic crystal CaF₂, is presented. The prototype gauge was calibrated at the National Bureau of Standards over the pressure range 0–2.5 kilobars, and the defining equation was found to be $${\mathrm{C/C}}_0{\text{=1−AP+BP}}^2$$ , where C₀ is the zero pressure capacitance, C is the capacitance at absolute pressure P, and the characteristic constants A and B are $${\text{A=3.7801×10}}^{\text{−6}}\mathrm{/(}\mathrm{bar})$$ and $${\text{B=2.739×10}}^{\text{−11}}\mathrm{/(}\mathrm{bar}{)}^2$$ . The gauge is stable and accurate over this range at the 0.01% level, and indications are that this type of gauge may be useful at much higher pressures and refined to even higher accuracies.