ISO 3567:2011 download free

07-01-2021 comment

ISO 3567:2011 download free.Vacuum gauges-Calibration by direct comparison with a reference gauge.
ISO 3567 specifies the physical, technical and metrological conditions to ti. fulfilled when calibrations of vacuum gauges are performed by dimct comparison with a reference gauge. From the conditions desalbed. the design of an epparatus thai can perlorm vacuum gauge calibrations in an adequate manner can be deduced.
The vacuum gauges to be calibrated can be of any kind. Many types of gauges consist of several parts. typicaly. these are: gauge head, cable, operational device and signal read out This entire set is considered as the unit that has to be calibrated. Whereas. it only the gauge head (ie. the part of the vacuum gauge directly exposed to the vacuum) is calibrated, all set-ups and conditions would have to be recorded such that the user of the calibrated gauge head would be able to perform the measurements in the same manner as during the calibration.
The reference gauge is either a calibrated gauge, traceable t a vacuum primary or national standard (normal case), with a calibration certificate according to ISOIEC 17025. or an absolute measuring instrument (rare case), traceable to the SI units and to which a measurement uncertatnty can be attributed.
ISO 3567 does not give guidance on how to treat special types of vacuum gauges, be they reference standards or units under calibration; it is intended that such guidance be given in other International Standards.
The pressure range icr calibrations treated in ISO 3567 depends on the realized design of the calibration apparatus and on the type of reference gauge. The range varies in its linits from 10 Pa to 110 kPa.
2 Normative references
The following referenced documents are Indispensable for the application of this document For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/1EC Guide 98-3. Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in maasw’ement (GLIM:1995)
ISOI1EC 17025:2005. General requirements for the competence of testing and calibration laboratories
3 Terms and definitions
For the purposes of ISO 3567, the following terms and definitions apply. primary standard
measurement standard established using a pnmary reference measurement procedure (SOURCE: ISO/1EC Guide 99:2007, 5.4, modified]
national standard
measurement standard recognized by national authority to serve in a state or economy as the basis for assigning quantity values to other measurement standards for the kind of quantity concerned
(SOURCE: ISOIIEC Guide 992007. 5.3]
5 General principle
The UUC is connected to the same calibration chamber as the reference gauge.
Calibration of a vacuum gauge — the UUC — by comparison with a reference gauge Is done by exposing the entrance flange of the UUC and that of the reference gauge to the same density and velocity distribution of calibration gas molecules. The same density and velocity distribution of these molecules means the same pressixe at the two locations, but not vice versa. Since there are many types of vacuum gauge that do not measure pressure — but instead, for example, gas density or the impingement rate of gas molecules — the above requisite is both necessary and more stringent than only calling for equal pressures at the two entrance flanges.
The gas density (pressure) in the cal4bratlon chamber can be vaned and the gauge readings of the UUC compared with the pressures indicated by the reference gauge.
From this general principle, the requirements (see Clause 6) for the design of the calibration apparatus are deduced.
6 Requirements
6.1 Design of calibration chamber
The chamber shall be designed to ensure that the distribution of gas in the measuflng volume is sufficiently uniform In space and stable in time.
In addition, the material of the calibration chamber shall be chosen such that the residual pressure. Pres. detemined by the effective pumping speed, qe (affective volume flow rate into pump), and the total oulgassing rate in the calibration chamber. Qwt (absence of leaks), is low enough to perform the calibrations, as expressed by Formula (1) (see also 6.3):
In detail, the calibration chamber shall be designed and operated as follows, However, design criteria a) to e) may be disregarded when the minimum pressures to be realized in the vacuum chanter are larger than 100 Pa and only static pressures (see 7.1) are established. Independent of pressure, criteria b) to d) may be disregarded when only static pressures are established
a) The calibration chamber shall have a volume of at least 20 times the total volume of all the gauges and associated pipe work connecting the chamber and the gauges (e.g. elbows shall be considered as part of the gauge volume).
b) The shape of the calibration chamber (see Figure 1) shall be cylinder-symmetrical to at least one axis. A sphere is ideal, but two symmetrical domes, each a part of a sphere and attached to one another, or cylinders, are equally possible. Where a cylinder is used, its overall length shall be within one and two bios its diameter, and domed ends are recommended,
c) The centre of the cross-sectionat area of the ptaiping outlet and the gas inlet (if applicable) shall lie on the same cylindrical axis of symmetry of the calibration chamber. The gas Inlet may be positioned between the pump outlet and pump system (see 8.3), in which case there is no need to have the gas inlet on the axis of symmetry.
d) All entrance mouths and their respective flanges to which either the UUCs or the reference gauges are to be connected shall be on a common equatorial plane, perpendicular to the cylindrical axis of symmetry chosen for the pumping outlet
Where a cylinder is used, it is recommended that this equatorial plane separate the cylinder into two halves of equal length. Where a cylinder with a length of (3/2)1) in relation to its diameter is used (suitable
6.3 Vacuum and gas Inlet system
6.3.1 The base pressure. p, In the calibration chamber shall be less than one tenth of the lowest pressure, p, reahzed for a calibration, as deterrmned by the reference gauge. The vacuum pump and its tubing to the calibration chamber shall be sized accordmy
Lowest uncertainties due to the base pressure effect can be achieved if the value of the base pressure is below the resolution limit of the UUC andlor reference gauge. It Is strongly recommended that a base pressure lower than the resokitlon limit of the UUC and?or reference gauge be established, If this resolution limit s greater than or equal tol mPa.
NOTE Where a low residual pressur, and base pressure In the calibration chamber is required, could be necessary to provide heatsg to the chamber to accelerate the removal of aorbed gases or vapours from the chamber walls.
6.3.2 A throughput pumping system that disd’targes the pumped gas continuously into the atmosphere is recommended. Ii no throughput pump is used. It shall be ensured that the effective pumping speed remains stable throughout the calibration procedure.
6.3.3 Any siiflcant back streaming of oil into the vacuum chamber shall be excluded.
6.3.4 The base pressure and residual pressure should be monitored using an extra gauge.
6.3.5 The gas frite may be provided either by admitting gas into the tubing between the calibration chamber and pump system or separately on the as of simetry of the calibration chamber If the latter option is chosen. th inlet shall be designed such that each gas molecule coming from the gas inlet has to make at least one hit with a wall of the calibration chamber or a baffle before it can enter the entrance mouth of the IJUC or reference gauge.
NOTE A vaNe reaclng the effective puning speed could help to reduce gas consumption. A corresponding riSe of residual pressure has to be considered as a trade-off.
6.4 Calibration gas
For the calibration gas, nitrogen 99.9 % pure or better Is reconwnended. Other gases of the same purity, even well-defined gas mixtures. may also be used for calibration. At pressures below 100 Pa the gases shall not stick significantly to the surface (sorption). Vapours shall not condense under calibration chamber conditions,
lithe gas purity is relevant for the uncertainty budget, the possibility has to be considered that the reservoir gas purity might not be present in the calibration chamber, due to desorbing gases between the gas reservoir and (including) the calibration chamber.
6.5 Thermometers and ambient conditions
Thermometers with an overall expanded uncertainty (A -2) of less than or equal to 0,5 K shall b used. The temperature of the calibration chamber shall be measured by means of thermometers In good thermal contact with the chamber. The ambient temperature around the UUC and the reference gauge shall be determined by means of thermometers suitably positioned and protected from radlation
The ambient temperature shall be (23±3) ‘C and should not change by more than 1 K during the calibrahoit If a change of more than 1 K is unavoidable, special care shall be taken so that the uncerbenty contributions due to temperature drill are correctly evaluated.
The ambient comdlition addressed by 6.2.3 also has to be considered. In addition, the ambient air flow andlor thermal radiation in the calibration room shall be such that the temperature condition according to 6.1 e) can be fulfilled.

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