โ Scribed by K.J. Close; R.S. Vaughan-Watkins; J Yarwood
No coin nor oath required. For personal study only.
A compact stainless-steel ultra-high vacuum system is designed, constructed and tested which enables any vacuum gauge to be calibrated absolutely, quickly and reliably over the pressure range 10 torr to 10 -8 torr. Experiments confirm that such gauge calibration can be carried out accurately without the large-scale equipment normally associated with a standards laboratory. The system is of the dynamic gas flow type in which, by the use of a combination of a silicon carbide porous plug and an orifice, both of known molecular conductance, a reduction of a reference pressure by a factor of about 105 is achieved and where this ratio is known and is independent of the molecular mass of the gas. Such a dynamic system enables satisfactory conditions to be established with quite modest pump speeds. A McLeod gauge of a design to operate over the pressure range 10 torr to 10 -1 torr is used to measure the reference pressure p,er of the test gas, which gas is expanded by a measured volume ratio of approximately 100 times and then reduced in pressure a further 10 S times by the novel dynamic flow method described, so achieving a final pressure of lO-7p,o~.
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