oSIST prEN 1518:2025

• Abstract:

  This document defines terms and specifies procedures for the characterization of mass spectrometer leak detectors (MSLD). This document is not intended to provide a complete set of specifications for acceptance testing, but rather a description of procedures that can be applied without specialized calibration equipment.; The methods described in this document are applicable without restrictions to helium as the tracer gas. For other gases, additional precautions might be necessary.; These methods are applicable to commonly available MSLD, based on the present level of technology, which might be able to measure leakage rates down to 10−12 Pa⋅m3/s.

• Status: Not Published
• Public Enquiry End Date: 30-Jan-2025
• ICS: 19.100 - Non-destructive testing
• Technical Committee: PKG - Testing of metallic materials
• Current Stage: 5020 - Formal vote (FV) (Adopted Project)
• Start Date: 17-Aug-2026
• Due Date: 05-Oct-2026
• Completion Date: 18-Aug-2026
• Ref Project: EN 1518:2026 - Non-destructive testing - Leak testing - Characterization of mass spectrometer leak detectors

• Revises: SIST EN 1518:2000 - Non-destructive testing - Leak testing - Characterization of mass spectrometer leak detectors
• Effective Date: 20-Dec-2023

oSIST prEN 1518:2025 is a CEN standard for non-destructive testing and leak testing that defines terms and procedures for characterizing mass spectrometer leak detectors (MSLD). It is aimed at people who need to measure or compare detector performance, using procedures that can be applied without specialized calibration equipment. The methods are written for helium as the tracer gas, and other gases may require extra precautions.

What does oSIST prEN 1518:2025 specify?

oSIST prEN 1518:2025 specifies the terminology and test procedures used to characterize mass spectrometer leak detectors. It is not a full acceptance-test specification; it gives practical methods for performance characterization that can be carried out with standard test arrangements.

The document is organized into nine clauses:

• Clause 1 - Scope
• Clause 2 - Normative references
• Clause 3 - Terms and definitions
• Clause 4 - Description of an MSLD
• Clause 5 - Apparatus for methods of characterization
• Clause 6 - Reference conditions for characterization
• Clause 7 - Test procedures
• Clause 8 - Results
• Clause 9 - Test report

Clause 4 explains how MSLD work and identifies the main parts of the instrument. Clauses 5 to 8 describe the test arrangement, the reference conditions, the measurement steps, and the way results are evaluated and reported.

What are the key requirements of oSIST prEN 1518:2025?

oSIST prEN 1518:2025 focuses on controlled test conditions, known leaks, and repeatable data processing. In practice, this means the detector must be prepared in a defined state, measured against reference leaks, and reported with the conditions needed to interpret the numbers.

Test setup and preparation

Clause 5 requires two known leaks: a small tracer gas leak for minimum detectable leakage rate and a large air leak for minimum detectable concentration. The leaks need temperature correction, because their output can change with ambient temperature, and that affects the measured detector performance.

Clause 5 also requires a test vessel for inlet pumping speed measurements. The vessel is a known-volume vacuum chamber with suitable metal construction and low leak tightness, so the pumping response of the MSLD can be calculated from a real test volume.

Before testing, Clause 5 requires the MSLD to be connected to the specified power supply, warmed up, adjusted for optimum tracer gas detection, and held at constant pumping speed or constant compression ratio if those settings are adjustable. In practice, this keeps the detector state stable so the measurements reflect the instrument rather than changing settings.

Reference conditions

Clause 6 sets reference conditions for ambient temperature, pressure, and humidity. The recommended values are given in the standard, and any other values used have to be stated in the test record.

This matters because leak detector response can vary with the environment. If the reference conditions are not recorded, results from different tests are hard to compare.

Minimum detectable leakage rate

Clause 7.2 and Clause 8.1 define how to determine the minimum detectable leakage rate. The procedure starts by measuring background drift and noise, then checks the auxiliary pumping system background, then measures sensitivity with a small calibrated leak.

The result is calculated from the minimum detectable signal and the measured sensitivity, and the time constant must be stated with it. In practice, this gives a realistic lower limit for leak detection under the test conditions, not just a nominal instrument claim.

Minimum detectable concentration

Clause 7.3 and Clause 8.2 define the minimum detectable concentration ratio. The method uses scan data around the tracer-gas peak, background correction, and signal smoothing to separate the tracer-gas contribution from the background.

For the reader, this means the instrument must be able to scan and resolve the tracer-gas peak clearly enough for weak concentrations to be distinguished from background. The result is useful when the detector is used to judge trace gas concentration rather than leak rate alone.

Inlet pumping speed for tracer gas

Clause 7.4 and Clause 8.3 define how to determine inlet pumping speed for tracer gas using the test vessel. The vessel response is recorded after the leak is closed, and the time constant is used to calculate pumping speed.

This is important when the detector is connected to a real test volume, because inlet pumping speed affects how fast the system responds and how quickly the tracer gas signal falls after the leak is isolated.

Test report

Clause 9 requires the report to identify the document used, the method, the results with reference conditions, the tracer gas, measurement uncertainty, operating mode, deviations, unusual features, and the test date. That gives a buyer, auditor, or laboratory a complete record of how the characterization was done and how to interpret the result.

What terms does oSIST prEN 1518:2025 define?

oSIST prEN 1518:2025 defines the terms needed to describe MSLD design, operation, and performance limits.

• Mass spectrometer leak detector (MSLD) - an instrument that uses a mass spectrometer and a vacuum system to measure tracer gas associated with leakage.
• Compression ratio - the ratio of tracer gas partial pressure at the exhaust of the counterflow stages to the partial pressure at the inlet of the mass spectrometer.
• Inlet pumping speed - the volume rate of flow at the test port when the instrument operates below the maximum working pressure of the MS; it influences response time.
• Optimum working pressure - the pressure in the MS at which the minimum detectable concentration can be measured.
• Maximum working pressure - the pressure in the MS above which operation is no longer possible.
• Minimum detectable concentration ratio - the smallest tracer gas concentration in an air mixture that can be detected unambiguously at optimum working pressure.
• Background signal drift - the slow change in background signal over time.
• Display resolution - the ability of the leakage-rate display to distinguish between closely spaced values.

Who uses oSIST prEN 1518:2025?

oSIST prEN 1518:2025 is used by people who characterize, compare, or verify MSLD in non-destructive testing and leak testing work. That includes test laboratories, instrument manufacturers, quality teams, and technical buyers who need a common way to describe detector capability.

It is especially useful when a team needs to document minimum detectable leakage rate, minimum detectable concentration, inlet pumping speed, or operating conditions for a detector. In practice, it supports performance comparison and technical reporting rather than a full acceptance-test regime.

What changed in oSIST prEN 1518:2025 from the previous edition?

oSIST prEN 1518:2025 replaces EN 1518:1998. The revision states these technical changes:

• updated normative references
• revised terms and definitions
• added a new general subclause in Clause 4
• updated Clause 5.2
• adapted the ambient temperature in Clause 6.1
• revised Clauses 7 and 8
• revised the test report
• integrated the figures into the text

Which standards are used with oSIST prEN 1518:2025?

oSIST prEN 1518:2025 uses EN ISO 20484:2017 for leak-testing vocabulary. That reference provides the general terminology that the standard builds on in Clause 3.

ISO 3530 is cited in the bibliography and is used in connection with the 63% rise-time definition of the signal processing time constant. It supports the way the document treats response timing in leak-detector evaluation.

What does the oSIST prEN 1518:2025 document contain?

oSIST prEN 1518:2025 contains definitions, instrument descriptions, test hardware requirements, measurement procedures, and result-evaluation methods. It also includes the formulas and plotting methods used to derive minimum detectable leakage rate, minimum detectable concentration, and inlet pumping speed.

The document shows the detector layouts and test arrangements for direct flow and counterflow operation. It also includes the vessel arrangement for inlet pumping speed, scan interpretation for tracer-gas peaks, and a flowchart for evaluating the minimum detectable signal.

Clause 7 gives step-by-step acquisition procedures, including background recording, leak-opening and leak-closing sequences, and scan measurements over defined time periods. Clause 8 then turns those records into reported values by applying regression, smoothing, background correction, and time-constant evaluation.

Clause 9 sets the minimum content of the test report so the characterization can be traced and repeated.

SLOVENSKI STANDARD
01-januar-2025
Neporušitveno preskušanje - Preskus tesnosti – Karakterizacija masno-
spektrometričnih detektorjev puščanja
Non-destructive testing - Leak testing - Characterization of mass spectrometer leak
detectors
Zerstörungsfreie Prüfung - Dichtheitsprüfung - Charakterisierung von
massenspektrometrischen Leckdetektoren
Essais non destructifs - Contrôle d’étanchéité - Caractérisation des détecteurs de fuite à
spectrométrie de masse
Ta slovenski standard je istoveten z: prEN 1518
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
prEN 1518
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2024
ICS 19.100 Will supersede EN 1518:1998
English Version
Non-destructive testing - Leak testing - Characterization of
mass spectrometer leak detectors
Essais non destructifs - Contrôle d'étanchéité - Zerstörungsfreie Prüfung - Dichtheitsprüfung -
Caractérisation des détecteurs de fuite à spectrométrie Charakterisierung von massenspektrometrischen
de masse Leckdetektoren
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 138.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 1518:2024 E
worldwide for CEN national Members.

prEN 1518:2024 (E)
Contents Page
European foreword . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
Terms . 5
3.1.1 Terms related to the MSLD . 5
3.1.2 Terms related to the operation of the MSLD . 6
3.1.3 Terms related to the specification of the MSLD . 7
3.1.4 Terms relating to the tracer gas background signal . 7
3.1.5 Terms relating to the detection limit. 7
3.1.6 Terms relating to the display resolution . 7
4 Description of an MSLD . 8
General. 8
Main parts of an MSLD . 8
Operating principles of MSLD . 9
4.3.1 Direct flow leak detectors . 9
4.3.2 Counterflow leak detectors . 9
MLSD specification . 9
5 Apparatus for methods of characterization . 10
Leaks . 10
5.1.1 General. 10
5.1.2 Small tracer gas leaks . 10
5.1.3 Large air leak . 10
Leak isolation valve. 10
Test vessel . 11
Arrangement for test . 12
5.4.1 Auxiliary pumping system . 12
5.4.2 Materials . 13
Preparation for test . 13
5.5.1 Power supply . 13
5.5.2 Warming up . 13
5.5.3 Adjustment . 13
5.5.4 Constant pumping speed . 13
5.5.5 Constant compression ratio of the high vacuum pump . 13
6 Reference conditions for characterization . 13
Reference temperature . 13
Reference pressure . 13
Reference humidity . 13
7 Test procedures . 14
General. 14
Minimum detectable leakage rate . 14
7.2.1 Background drift and noise . 14
7.2.2 Auxiliary pumping system background . 14
7.2.3 Sensitivity . 14
prEN 1518:2024 (E)
7.2.4 Time constant . 15
Minimum detectable concentration . 15
7.3.1 General . 15
7.3.2 Background drift and noise . 17
7.3.3 Background signal . 17
7.3.4 Sensitivity . 17
Inlet pumping speed for tracer gas . 18
8 Results . 18
Minimum detectable leakage rate . 18
8.1.1 Evaluation. 18
8.1.2 Expression of minimum detectable leakage rate . 20
Minimum detectable concentration . 20
8.2.1 Evaluation. 20
8.2.2 Expression of minimum detectable concentration . 21
Inlet pumping speed . 21
8.3.1 Evaluation. 21
8.3.2 Expression of inlet pumping speed . 22
9 Test report . 22
Bibliography . 24

prEN 1518:2024 (E)
European foreword
This document (prEN 1518:2024) has been prepared by Technical Committee CEN/TC 138 “Non-
destructive testing”, the secretariat of which is held by AFNOR.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 1518:1998.
prEN 1518:2024 includes the following significant technical changes with respect to EN 1518:1998:
a) normative references have been updated;
b) clause “Terms and definitions” has been revised;
c) new Subclause 4.1, General, has been added;
d) Clause 5.2 has been updated;
e) in Clause 6.1, the ambient temperature has been adapted;
f) Clause 7 and 8 have been revised;
g) the test report has been revised;
h) the figures have been integrated in the text.
prEN 1518:2024 (E)
1 Scope
This document specifies terms and procedures for the characterization of mass spectrometer leak
detectors (MSLD). It is not intended to give a complete set of specifications for an acceptance test but a
description of procedures that can be used without particular calibration equipment.
The methods described in this document are applicable without restrictions to helium as the tracer gas.
For other gases, additional precautions may be necessary.
These methods are applicable to commonly available MSLD, based on the present level of technology,
−12 3
which may be able to measure leakage rates down to 10 Pa⋅m /s.
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.
EN ISO 20484:2017, Non-destructive testing — Leak testing — Vocabulary (ISO 20484:2017)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN ISO 20484:2017 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
Terms
3.1.1 Terms related to the MSLD
3.1.1.1
compression ratio
ratio of partial pressure of tracer gas with zero flow at the exhaust of the counterflow stages of the high
vacuum pump to the partial pressure at the inlet of the mass spectrometer (MS)
3.1.1.2
display
device which indicates visually the leakage rate measured
Note 1 to entry: The units in which the leakage rate is expressed can be selectable.
Note 2 to entry: The display can be analogue or quasi-analogue (continuous scale with definite divisions) or digital
(numbers with a definite number of digits) or a combination of both.
3.1.1.3
inlet pumping speed
volume rate of flow at the test port of an MSLD when the instrument is operating with the MS below its
maximum working pressure
Note 1 to entry: The inlet pumping speed can be different for different gases and different modes of operation. The
inlet pumping speed for the tracer gas determines the response time for the volume under test.
prEN 1518:2024 (E)
3.1.1.4
internal leak port
flange directly behind the inlet valve, used to connect a small leak for zero drift determination
3.1.1.5
intrinsic pumping speed
volume rate of flow of tracer gas at the inlet of the MS in a direct flow leak detector
3.1.1.6
ion collector
part of the MS where ions are collected and neutralized producing a current in the collector which is a
measure of the number of neutralized ions
3.1.1.7
sensitivity control
electrical hardware or software control which may be used to adjust the sensitivity of the instrument so
that a calibrated leak is indicated with its true leakage rate
3.1.1.8
sensitivity
ratio of the ion current at the output of the MS to the corresponding partial pressure of tracer gas inside
the MS
3.1.1.9
zero control
electrical hardware or software control which may be used to shift the output indication of the leak
detector, to a determined point of the scale range in use, usually zero
3.1.2 Terms related to the operation of the MSLD
3.1.2.1
peak
trace showing a maximum when the leak detector is scanned with respect to mass with gas
present, usually the tracer gas, to which the detector is tuned
3.1.2.2
peak
to set the scanning control (see 3.1.2.3) of a leak detector so that the output due to a given tracer
gas input is maximized
Note 1 to entry: It is a form of tuning (see 3.1.2.4).
3.1.2.3
scan
to adjust the accelerating voltage (or other equivalent operating parameter) of a leak detector,
particularly across that range of voltage which includes the voltage necessary to produce a tracer gas
peak
3.1.2.4
tune
in leak detection, to adjust one or more of the controls of a leak detector so that its response to a
tracer gas is maximized
Note 1 to entry: Tuning by means of the scanning control only is called “peaking” (see 3.1.2.2).
prEN 1518:2024 (E)
3.1.3 Terms related to the specification of the MSLD
3.1.3.1
optimum working pressure
pressure in the MS, at which the minimum detectable concentration can be measured
3.1.3.2
maximum working pressure
pressure in the MS above which operation is no longer possible
3.1.3.3
maximum inlet pressure
maximum pressure at the test port at which the MSLD is able to detect leaks in a given mode of operation
Note 1 to entry: For an MSLD to be connected directly to a system under test, the total pressure in the system shall
be less than the maximum inlet pressure of the MSLD.
3.1.3.4
maximum gas load
maximum pV-throughput of all gases emerging from the test specimen that the MSLD can pump during
leak detection in a given mode of operation
Note 1 to entry: For component testing, the MSLD is normally ready for measurement when the desorption of
water vapour from the inner surfaces is less than the maximum gas load.
3.1.4 Terms relating to the tracer gas background signal
3.1.4.1
background signal drift
relatively slow change in background signal, given by the maximum change in a given period of time
3.1.4.2
background signal noise
relatively rapid change in background signal given by an average measure of scatter in a specified period
of time
3.1.5 Terms relating to the detection limit
3.1.5.1
minimum detectable concentration ratio
smallest concentration of a given tracer gas in an air mixture that can be detected unambiguously when
the mixture is fed into the MSLD at such a rate as that is at its optimum working pressure
3.1.5.2
resolving power
ratio of a given mass number to the peak width measured at a specified (for example 10 %) height of the
peak (in units of mass numbers)
3.1.6 Terms relating to the display resolution
3.1.6.1
display resolution
quantitative expression of the ability of the leakage rate-display device to distinguish meaningfully
between closely adjacent values of the leakage rate indicated
prEN 1518:2024 (E)
3.1.6.2
linear display resolution
constant difference between adjacent scale intervals expressed in % full scale indication
3.1.6.3
logarithmic display resolution
constant ratio between two adjacent scale intervals expressed as a percentage of the indicated value
4 Description of an MSLD
General
An MSLD has an integral high vacuum system for maintaining the sensing element (mass spectrometer)
at low operating pressure and for establishing a partial pressure related to the incoming gas flow. This
pressure is measured quantitatively by the mass spectrometer. Such instruments are able to selectively
measure the flow of a tracer gas. In most cases the tracer gas will be helium, flowing in/out of an object
through a leak.
MSLD are commonly operated in either direct or counterflow configurations. These are both illustrated
in Figure 2.
Main parts of an MSLD
An MSLD (see definition given in EN ISO 20484) consists basically of a mass spectrometer (MS) and a
high vacuum pumping system for:
— maintaining the MS under appropriate vacuum conditions;
— producing a definite partial pressure of tracer gas when a specific throughput of tracer gas enters the
leak detector.
An MSLD includes also a number of valves and pressure gauges to ensure the appropriate vacuum
conditions within the system.
The leakage rate output can be displayed in a number of ways, for example an electrical meter, or digital
displays of different types, such as with a logarithmic or linear display resolution. In addition, a digital
and/or analogue output is usually available, which shall be used for the test procedures in this document.
The general structure of an MSLD is described by the following list:
a) mass spectrometer:
— ion source;
— separation system;
— ion collector.
b) pumping system:
— inlet system;
— inlet line;
— inlet valve;
— pump valve;
prEN 1518:2024 (E)
— test port;
— vent valve;
— internal leak port.
c) sensitivity zero control.
d) display.
Operating principles of MSLD
4.3.1 Direct flow leak detectors
The leakage rate is given by the formula:
q
x
(1)
q pS⋅
x xx
where
is the pV-throughput of tracer gas;
q
x
is the intrinsic pumping speed;
S
x
is the partial pressure of tracer
...