ISO 19685:2017 真空技術—真空計—ピラニゲージの仕様、校正、および測定の不確かさ | ページ 2

3.1 コンポーネントの定義

3.2 物理パラメータの定義

3.2.3

長期的な不安定性

相対測定誤差の典型的な変化を特徴付ける量期間を指定する必要がある場合

注記1:このゲージタイプの長期不安定性を決定するための測定誤差は、 一定時間経過後のPa（窒素）。この量δ _tは相対量であり、次の 2 つの方法で決定できます。

• a)測定誤差e _iの相対標準偏差

  

ここで、 nはキャリブレーションiの数であり、

• b)指定された期間で区切られた再校正間の測定誤差 Δ p _iの絶対的な (負ではない) 変化の平均として

  

およびnは上記のとおり

注記2 a)の式は測定誤差が有意なドリフトではなくランダムな変動を示す場合に推奨され，b)の式は測定誤差が系統的で単調なドリフトを示す場合に推奨される。

注記3ゲージの出力信号が圧力でない場合(電圧または電流など)、この信号は、測定誤差を計算する前に、メーカーの仕様に基づいて圧力に変換する必要があります。

注記 4:長期不安定性は、より正確なゲージまたは一次標準を使用した再校正によって決定できます。多くの場合、これにはトランスポートが必要であり、それ自体が校正値の不安定性につながる可能性があります。このため、時間に対する不安定性の線形関係を仮定することは合理的ではありません (たとえば、2 年間の δ _tは 1 年間のδ _tの 2 倍ではありません)

注記 5別段の指定がない限り、 δ _tを 1 年間にわたって決定することが推奨される。これは通常、コストと輸送の影響との間の妥当な妥協点であり、他方ではドリフトの可能性と測定の不確実性を最小限に抑えることです。

例：

b) の式に従ってδ _tが 6.5% と決定され、再校正期間が 1 年である場合、レポートは「 δ _t = 1 年間で 6.5%」となります。

3.2.4

反応時間

τ

ピラニゲージが 1 kPa から 100 Pa の間の窒素の急激な圧力変化 (上または下で指定) にさらされたときに、ピラニゲージが圧力変化差の 90% を示すまでに経過する時間。

注記 1:図 1 を参照。

図 1 —応答時間 τ の定義を説明する図

Foreword

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This document was prepared by Technical Committee ISO/TC 112, Vacuum technology.

Introduction

ISO 3567 and ISO 27893 are basic standards with no specific guidelines of a special type of vacuum gauge and are generally applicable. Detailed guidance for a specific gauge is intended to be given in separate technical specifications for the calibration of special types of gauges.

This document complements ISO 3567 and ISO 27893 when characterizing or calibrating Pirani gauges or using them as reference gauges.

Pirani gauges are widely used to measure pressures in the medium vacuum up to atmospheric pressure. The relevant parameters, calibration guidelines and uncertainties for the dissemination of the pressure scale and measurement of low and medium vacuum pressures by a Pirani gauge are described in this document.

1 Scope

This document identifies parameters of Pirani gauges, their calibration procedure, and describes measurement uncertainties to be considered when operating these gauges.

This document applies to Pirani vacuum gauges operating over a pressure range of 0,01 Pa to 150 kPa.

This document complements ISO 3567 and ISO 27893 when calibrating Pirani gauges and using them as reference standards.

In addition, this document defines procedures to characterize Pirani gauges for response time and hysteresis.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements 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.

3 Terms and definitions

For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

3.2 Definitions of physical parameters

3.2.1

internal volume

volume of the gauge that is exposed to the vacuum system where it is attached to, counted from the connecting flange plane

3.2.2

thermal accommodation coefficient

ratio of the absolute temperature of the molecule after a hit with the heated element in a Pirani gauge and the absolute temperature of the heated element

3.2.3

long-term instability

quantity characterizing the typical change of relative measurement error over time where the period needs to be specified

Note 1 to entry: Measurement errors to determine long-term instability of this gauge type are taken for nitrogen at a pressure of Pa (nitrogen) after a specified period. This quantity δ_t shall be a relative quantity and may be determined in two ways:

• a) as the relative standard deviation of measurement error e_i obtained from at least three calibrations each being separated by the specified period

  

with n being the number of calibrations i, and

• b) as the mean of absolute (non-negative) changes of measurement error Δp_i between recalibrations separated by the specified period

  

and n as described above

Note 2 to entry: The formula in a) is recommended when the measurement error does not show a significant drift but random variations, and the formula in b) when the measurement error shows a systematic and monotonic drift.

Note 3 to entry: If the output signal of the gauge is not pressure (e.g. voltage or current), this signal shall be converted to pressure based on the manufacturer's specification, before the measurement error is calculated.

Note 4 to entry: Long term instability can be determined by recalibrations with a more accurate gauge or a primary standard. This often requires a transport which itself can lead to an instability of the calibrated value. For this reason, it is not reasonable to assume a linear relationship of instability with time (e.g. δ_t for a period of 2 years is not 2 times δ_t for a period of 1 year).

Note 5 to entry: If not specified otherwise, it is recommended to determine δ_t over a period of 1 year. This is usually a reasonable compromise between costs and influence of transport on the one hand and a possible drift and lowest possible measurement uncertainty on the other hand.

EXAMPLE:

If δ_t was determined to 6,5 % according to the formula in b), where the period of recalibration was 1 year, the report will be “δ_t = 6,5 % for a period of one year”.

3.2.4

response time

τ

time that elapses when the Pirani gauge is exposed to a sudden pressure change of nitrogen between 1 kPa to 100 Pa (up or down to be specified), until the Pirani shows 90 % of the pressure change difference

Note 1 to entry: See Figure 1.

Figure 1—Illustration to explain definition of response time τ

3.2.5

hysteresis

relative difference of indication of a Pirani gauge when exposed to the same pressure in a rising and decreasing sequence

Bibliography