New, fully automated, primary standard for generating vacuum pressures between 10 ¹⁰Pa and 3   10 ²Pa with respect to residual pressure

Abstract

A new primary standard for the realization of vacuum pressures between 10 -10 Pa and 3 ϫ 10 -2 Pa has been completed at the Physikalisch-Technische Bundesanstalt (PTB). It is based on the continuous expansion method, whereby the range is extended to lower pressures by the use of a flow divider. In this flow divider, the gas flow from the fully automated flowmeter with throughputs ranging from 10 -6 Pa l/s up to 3 Pa l/s (at 23 C) is directed via two differently sized orifices into two chambers: the XHV calibration chamber, which is designed for calibration pressures 10 -10 Pa to 10 -4 Pa, takes up 1 % of the flow, while the UHV calibration chamber, which is designed for pressures 10 -8 Pa to 3 ϫ 10 -2 Pa, takes up 99 % of the flow. Both calibration chambers are operated with cryopumps during calibration. The relative standard uncertainties of pressures generated by this new standard range from 7 ϫ 10 -3 at 10 -10 Pa, when a perfectly stable residual pressure is assumed, to 2 ϫ 10 -3 at 10 -4 Pa.

Final report of key comparison CCM.P-K3: absolute pressure measurements in gas from 3 × 10−6Pa to 9 × 10−4Pa

“…The primary standard at PTB is a continuous expansion system, called CE3 [3], with its flowmeter FM3 [4]. Known gas flow is injected into a flow divider chamber, which then flows into either a UHV chamber through a larger conductance orifice or into a XHV (extreme high vacuum) chamber through a smaller conductance orifice with about 1/100 of the conductance to the UHV chamber.…”

“…The leak was immediately redressed. Also it was found that the small orifice C 02 [3] (nominal diameter 700 µm) from the flow divider into the XHV chamber was dented and had changed its dimension, probably due to a high differential pressure during a pump down process after venting. The conductance was re-measured.…”

Constant pressure primary flow standard for gas flows from 0.01cm3/min to 100cm3/min (0.007–74μmol/s)

“…Jousten [12] s Calibrated bellows 12 5 Â 10 À 6 0.05 0.15 Jitschin [13] s Pistonþ lubricated o-rings 25 5 Â 10 À 4 50 0.1 Li [14] s/r Pistonþ bellows þ oil-filled cylinder 10, 25 5 Â 10 À 6 13 2. Jousten [15] s Calibrated bellows 12 5 Â 10 À 7 13 0.2 Jousten [16] s Calibrated bellows 12 5 Â 10 À 7 13 0.14 Calcatelli [17] s Pistonþ cylinderþ custom PTFE seal 5, 20 1 Â 10 À 5 0.7 0.2 Berg [18] s/r Pistonþ bellows þ oil-filled cylinder 102 1 Â 10 À 1 270 0.02 Cignolo [19] s/r Pistonþ lubricated o-ring 120 9 Â 10 À 2 1900 0.01 Kramer [20] s/r Double piston 16 1 Â 10 À 3 1.3 0.03 Cheng [21] s Pistonþ bellows þ oil-filled cylinder ? 5 Â 10 À 6 0.05 0.57 Gronych [22] s Calibrated bellows 9,30 3 Â 10 À 4 55 1.…”

“…The third type of flow standard, calibrated bellows [12,15,16,22], also has no sliding seal, and it eliminates the complications due to the oil by driving the bellows directly. Its chief disadvantage is that the bellows volume V(x) must be calibrated as a function of its linear displacement x. Jousten et al [12] found that V(x) was more linear for a formed bellows than for a welded diaphragm bellows, although Gronych et al [22] later were able to use a welded diaphragm bellows despite its nonlinearity.…”

The development of vacuum measurements down to extremely high vacuum – XHV

“…Such devices are, generally, made of a calibration chamber connected to the pumping chamber through a conductance. The pumping system is, frequently, a combination of mechanical and turbo molecular pumps and the conductance is as near as possible to a hole in a thin wall to be able to calculate its value by analytical [98,99] or by Monte Carlo methods [100,101].Those systems need to be equipped with a gas flow generating and measuring unit that is frequently based on the variable-volume and constant-pressure method [102,103]. In the simple realization the lower limit may be between 10-6 and 10-7 Pa. For lower pressure, on the historical point of view it should be mentioned the PTB molecular beam system realized several years ago by G. Messer and G. Grosse [104,95].…”