1.4 Fast volume determination using a differential capacitance manometer

The reliable pressure readings with a capacitance manometer are the basis for a new type of instrument designed for accurate and rapid measurements of capillary volumes. The basic measuring principle is based on expansion of air atmospheric pressure enclosed in a known volume into a pre-evacuated cylinder so that the enclosed volume will cause a reduced pressure in the cyllinder. The same is done with the air in an unknown volume into another identical pre-evacuated cylinder. A differential capacitance manometer is then used to measure the difference in pressure between the two cylinders with a high degree of accuracy. This difference in pressure is shown to be ainear function of the difference in volume between the unknown and the known volume. The accuracy and repeatability of the instrument is better than 0.5%.