Static expansion vacuum standard with extended low pressure range

The main factor to affect lower limit of static expansion vacuum standard is outgassing of the inner surface. A new method has been demonstrated to extend the lower limit by using a non-evaporable getter pump (NEGP) to eliminate the outgassing influence. Because NEGP has no pumping speed for inert gases, it can maintain the ultra-high vacuum background without changing gas quantity in the calibration chamber when an inert gas is used as the test gas, which makes the standard pressure accurately calculable by Boyle’s law. By this method, the lower limit of static expansion vacuum standard has been extended to 10⁻⁷ Pa.