ISO/TS 6737

Vacuum technology — Vacuum gauges — Characteristics for a stable ionisation vacuum gauge

This document describes a special design of an ionisation vacuum gauge which has a well-defined ionising electron path length. Due to the construction design, it promises good measurement accuracy, long-term stability, as well as gauge independent and reproducible relative sensitivity factors It is designed for the measurement range of 10-6 Pa to 10-2 Pa. This document describes only those dimensions and potentials of the gauge head which are relevant for the electron and ion trajectories. This document does not describe the electrical components necessary to operate the ionisation vacuum gauge in detail. The gauge head can be operated by voltage and power sources and current meters commercially available, but also by a controller specially built for the purpose of the operation of this gauge head. The ionisation vacuum gauge described in this document can be built by any experienced manufacturer of other ionisation vacuum gauges. It is assumed for this document that the applicant is familiar with both the physics and principles of ionisation vacuum gauges as well as high and ultra-high vacuum technology in general.

Technique du vide — Manomètres à vide — Caractéristiques des manomètres à ionisation stable

General Information

• Status: Not Published
• ICS: 23.160 - Vacuum technology
• Technical Committee: ISO/TC 112 - Vacuum technology
• Drafting Committee: ISO/TC 112 - Vacuum technology
• Current Stage: 6000 - International Standard under publication
• Completion Date: 02-Sep-2023

Standards Content (Sample)

ISO/TC 112
ISO/CD TSDTS 6737(en:2023(E)
Date:2023-06-22
Secretariat:  DIN
Vacuum technology — Vacuum gauges — Characteristics for a stable ionisation vacuum gauge
Technique du vide — Manomètres à vide — Caractéristiques des manomètres à ionisation stable

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ISO/CD TS 6737:2023(E)
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this
publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical,
including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can
be requested from either ISO at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
E-mail: [e-mail]
Website: www.iso.orgError! Hyperlink reference not valid.
Published in Switzerland
2 © ISO 2023 – All rights reserved
ii © ISO 2023 – All rights reserved

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ISO/CD TS 6737:2023(E)
Contents
Foreword . 3
Introduction. 3
Scope . 3
Normative references . 3
Terms and definitions . 3
Symbols and abbreviated terms . 3
General description of the design . 3
Components . 3
Mode of operation . 3
Specifications of the ionisation vacuum gauge . 3
General specifications and requirements for the gauge head . 3
Electrical equipment . 3
Dimensions and potentials . 3
General . 3
Dimensions and tolerances . 3
Potentials . 3
Cathode . 3
Anode cage . 3
Gaps between electrodes . 3
Electrode materials . 3
Electrical feedthroughs . 3
Surrounding tube (envelope) and flanges . 3
Magnetic fields . 3
Characteristics of the gauge (informative) . 3
Sensitivity . 3
Linearity . 3
Electron transmission efficiency . 3
Residual current and resolution . 3
Repeatability . 3
Reproducibility . 3
Interference . 3
Temperature of electrodes . 3
Environmental conditions . 3
Handling of and measurement with the gauge. 3
© ISO 2023 – All rights reserved 3
© ISO 2023 – All rights reserved iii

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ISO/CD TS 6737:2023(E)
Orientation of the gauge head . 4
Environmental conditions . 4
Conditioning of the gauge . 4
Testing . 4
Warm-up time . 4
Sensitivity and calibration . 4
Measurement . 4
Transport . 4
Cathode exchange . 4
Electron and ion trajectories of recommended gauge dimensions according to simulation . 4
Bibliography . 4

Foreword . 6
Introduction . 7
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and abbreviated terms . 2
5 General description of the design . 3
5.1 Components . 3
5.2 Mode of operation . 3
6 Specifications of the ionisation vacuum gauge . 5
6.1 General specifications and requirements for the gauge head . 6
6.2 Electrical equipment . 7
7 Dimensions and potentials . 7
7.1 General . 8
7.2 Dimensions and tolerances . 8
7.3 Potentials . 11
7.4 Cathode . 12
7.5 Anode cage . 12
7.6 Gaps between electrodes . 12
7.7 Electrode materials . 13
7.8 Electrical feedthroughs . 13
7.9 Surrounding tube (envelope) and flanges . 13
7.10 Magnetic fields . 13
4 © ISO 2023 – All rights reserved
iv © ISO 2023 – All rights reserved

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ISO/CD TS 6737:2023(E)
8 Characteristics of the gauge (informative) . 14
8.1 Sensitivity . 14
8.2 Linearity . 14
8.3 Electron transmission efficiency . 14
8.4 Residual current and resolution . 15
8.5 Repeatability . 15
8.6 Reproducibility . 15
8.7 Interference . 15
8.8 Temperature of electrodes . 15
8.9 Environmental conditions . 15
9 Handling of and measurement with the gauge . 15
9.1 Orientation of the gauge head . 15
9.2 Environmental conditions . 15
9.3 Conditioning of the gauge . 16
9.4 Testing . 16
9.5 Warm-up time . 16
9.6 Sensitivity and calibration . 16
9.7 Measurement . 16
9.8 Transport . 16
9.9 Cathode exchange . 16
Annex A (Informative) Electron and ion trajectories of recommended gauge dimensions according to
simulation . 17
Bibliography . 19

© ISO 2023 – All rights reserved 5
© ISO 2023 – All rights reserved v

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ISO/CD TS 6737:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documentsdocument should be noted. This document was drafted in accordance
with the editorial rules of the ISO/IEC Directives, Part 2 (see
www.iso.org/directiveswww.iso.org/directives).
Attention is drawnISO draws attention to the possibility that some of the elementsimplementation of this
document may beinvolve the subjectuse of (a) patent(s). ISO takes no position concerning the evidence,
validity or applicability of any claimed patent rights. in respect thereof. As of the date of publication of
this document, ISO had not received notice of (a) patent(s) which may be required to implement this
document. However, implementers are cautioned that this may not represent the latest information,
which may be obtained from the patent database available at www.iso.org/patents. ISO shall not be held
responsible for identifying any or all such patent rights. Details of any patent rights identified during the
development of the document will be in the Introduction and/or on the ISO list of patent declarations
received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation onof the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the World
Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT)), see the following URL:
www.iso.org/iso/foreword.htmlwww.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 112 ", Vacuum technology".
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at
www.iso.org/members.htmlwww.iso.org/members.html.
6 © ISO 2023 – All rights reserved
vi © ISO 2023 – All rights reserved

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ISO/CD TS 6737:2023(E)
Introduction
The ionisation vacuum gauge is the only vacuum gauge type in the full range of high and ultrahigh vacuum
[1]. The pertinent standardization committee for vacuum technology ISO TC 112 has indicated that
[1]
important. Important applications need better accuracy, reproducibility and known sensitivities for
many gas species, properties which all presentcurrent types of ionisation vacuum gauges lack. This
document provides the characteristics for a stable ionisation vacuum gauge so that this gauge is accurate,
robust and long-term stable, with known sensitivity for nitrogen and known relative sensitivity factors,
and can be built by any experienced manufacturer of other ionisation vacuum gauges.
© ISO 2023 – All rights reserved 7
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DRAFT TECHNICAL SPECIFICATION ISO 6737:2023(E)

Vacuum technology — Vacuum gauges — Characteristics for a
stable ionisation vacuum gauge
1 Scope
This document describes a special design of an ionisation vacuum gauge which has a well-defined ionising
[2]
electron path length[2]. Due to the construction design, it promisesleads to good measurement
accuracy, long-term stability, as well as gauge independent and reproducible sensitivity for nitrogen and
[3] -6 -2
relative sensitivity factors[3] It is designed for the measurement range of 10 Pa to 10 Pa.
This document describes only those dimensions and potentials of the gauge head which are relevant for
the electron and ion trajectories. This document does not describe the electrical components necessary
to operate the ionisation vacuum gauge in detail. The gauge head can be operated by voltage and power
sources and ammeters commercially available, but also by a controller specially built for the purpose of
the operation of this gauge head.
The ionisation vacuum gauge described in this document can be built by any experienced manufacturer
of other ionisation vacuum gauges. It is not subject to intellectual property protection.
It is assumed for this document that the applicant is familiar with both the physics and principles of
ionisation vacuum gauges as well as high and ultra-high vacuum technology in general.
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 13920:1996, Welding - General tolerances for welded constructions - Dimensions for lengths and
angles - Shape and position (ISO 13920:1996)
ISO 2768--1:,, General tolerances — Part 1: Tolerances for linear and angular dimensions without
individual tolerance indications
ISO 27894:, 3669, Vacuum technology — Vacuum gauges — Specifications for hot cathode ionization
gauges
ISO 3567: Vacuum gauges — Calibration by direct comparison with a reference gauge
ISO 3669: Vacuum technology — Bakeable flanges — Dimensions of knife-edge flanges
ISO/IEC Guide 98-1:2009, Uncertainty of measurement — Part 1: Introduction to the expression of
uncertainty in measurement
ISTA 2A:2011, Partial simulation tests for testing of individual packaged-products weighing 150 lbs (68 kg)
or less when prepared for shipment, published by the International Safe Transit Association.
© ISO 2023 – All rights reserved 1

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ISO/CD TS 6737:2023(E)
53 Terms and definitions
The Terms and definitions clause is a mandatory element of the text.
For rules on the drafting of the Terms and definitions, refer to the ISO/IEC Directives, Part 2:2018, Clause 16.
To insert a new terminological entry, go to the Structure tab and click on Insert Term entry.
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminologicalterminology databases for use in standardization at the following
addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
Wehnelt electrode or
Wehnelt
an electrode with cylindrical symmetry around the electron emitting cathode, mainly used for focusing
of the electron beam
3.2
Ionisationionisation space
the space in which ions generated by collision of gas molecules with high energy electrons reach the ion
collector by means of a suitable electrostatic field
3.3
Faraday cup
metal cup or other piece of metal designed to catch charged particles in vacuum
Note 1 to entry: In the ionisation vacuum gauge described in this document, the Faraday cup is designed to capture
the electrons emitted from the cathode
3.4
Envelope
envelope
the metallic wall at zero (earth) potential surrounding the gauge head at least in its full length
3.5
Electronelectron transmission
the ratio of electron current measured at the Faraday cup divided by the electron current emitted from
the cathode
64 Symbols and abbreviated terms
I ion current at pressure p [A]
I0 ion current at residual pressure p0 [A]
2 © ISO 2023 – All rights reserved
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ISO/CD TS 6737:2023(E)
I electron emission current [A]
e
p pressure [Pa]
p residual pressure [Pa]
0
[1]
r relative sensitivity factor as defined in ISO 27894:2009
x
S sensitivity (coefficient) [1/Pa]
S sensitivity for nitrogen [1/Pa]
N2

85 General description of the design

8.25.1 Components
The ionisation vacuum gauge consists of the following functional parts:
a) electron emitting cathode,
b) Wehnelt electrode,
c) anode cage in two parts,
d) ion collector,
e) electron deflector,
f) Faraday cup,
g) envelope.
The functional components a) to f) need to be exactly dimensioned.
In addition, the gauge needs electrical feedthroughs, wires, mounting parts and insulators. The gauge
shall be mounted on a DN40CF or on a DN63CF flange according to ISO 3669: with corresponding tube
sizes DN40 or DN63 as envelope.

8.45.2 Mode of operation
A schematic for the illustration of the operation of the gauge is shown in Figure 1,Figure 1, for a detailed
drawing see Figure 2Figure 2 in 7.2.7.2. For simplification, in Figure 1Figure 1 the anode cage (3) is not
been divided in two parts as in Figure 2Figure 2 with (3a) and (3b) and the collector ring (6) in between.
© ISO 2023 – All rights reserved 3
© ISO 2023 – All rights reserved 3

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ISO/CD TS 6737:2023(E)


Key
1 Cathodecathode with emitter disk (red)
2 Wehnelt cylinder
3 Anodeanode cage
4 Electronelectron deflector
5 Faradayfaraday cup
6 Ionion collector
+
I Ionion
-
e Electronelectron
Figure 1 — Illustration of mode of operation (informative)
Electrons are emitted from the hot thermionic cathode (1 in Figure 1Figure 1 and Figure 2),Figure 2),
which is preferably an indirectly heated disk emitter on a potential of 50 V. The Wehnelt electrode (2 in
Figure 1)Figure 1) surrounding the cathode has a lower potential and controls and focuses the electron
beam into the opening of the anode cage at 250 V.
4 © ISO 2023 – All rights reserved
4 © ISO 2023 – All rights reserved

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ISO/CD TS 6737:2023(E)
NOTE
InNote that in the future, it maycan be possible that the thermionic cathode can be replaced by a so-called
cold field emission cathode. This cathode shall be long-term stable and provide an electron current of
about 100 µA. In addition, it shall be ensured that the energy of the electrons along their path is not
changed compared to the design with thermionic cathode.
Due to the penetration of the anode potential into that of the Wehnelt electrode the electrons can be
extracted and accelerated into the inner part of the cylindrical anode cage. The first part of the anode cage
(3a at 250 V, see Figure 2),Figure 2), the ion collector ring (0 V, 6 in Figure 1Figure 1 and Figure
2)Figure 2) and the second remaining part of the anode cage (250 V, 3b in Figure 2)Figure 2) form an
electrostatic lens which focuses the electron beam into the circular exit of the anode cage. Behind this exit
the electron beam is deflected by the electron deflector electrode (45 V, 4 in Figure 1Figure 1 and Figure
2)Figure 2) in a U-turn onto the capturing part of the Faraday cup (280 V, 5 in Figure 1Figure 1 and
Figure 2).Figure 2). When the electrons hit the Faraday cup, they will generate X-rays. By the U-turn, it is
ensured that these X-rays have a very low probability to reach the ion collector or the anode where they
would generate secondary electrons.
The ions generated by the electron beam inside the anode cage are accelerated towards the ion collector
which consists of the mentioned ring and a rod reaching into the larger space of the anode cage. Ions
generated behind the exit of the cage are accelerated towards the electron deflector electrode. The
ionisation space is well defined in this design.
The measured ion current will be proportional to the gas density in contact with the electron beam, the
ionisation probability of the gas molecules by the electron impacts along their path, the mean path length
of the electrons inside the ionisation space and the electron current.
Due to the focused electron beam inside the anode cage, the electron current should not exceed 200 µA.
Higher currents can cause non-linearities.
The mean electron path length is defined by the length of the anode cage and the potential inside it. Any
changes of the emission points of the electrons on the cathode will not significantly change the path
length. A replacement of the same cathode type will have an insignificant influence on the path length.
Space charge effects of ions will also have an insignificant influence on the path length within the specified
measurement range up to 0,01 Pa. Due to the well-defined electron path length, the nitrogen sensitivity
and the relative sensitivity factors will not significantly vary from gauge to gauge except within t
...

FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 6737
ISO/TC 112
Vacuum technology — Vacuum
Secretariat: DIN
gauges — Characteristics for a stable
Voting begins on:
2023-07-07 ionisation vacuum gauge
Voting terminates on:
Technique du vide — Manomètres à vide — Caractéristiques des
2023-09-01
manomètres à ionisation stable
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 SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/DTS 6737:2023(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2023

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ISO/DTS 6737:2023(E)
FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 6737
ISO/TC 112
Vacuum technology — Vacuum
Secretariat: DIN
gauges — Characteristics for a stable
Voting begins on:
ionisation vacuum gauge
Voting terminates on:
Technique du vide — Manomètres à vide — Caractéristiques des
manomètres à ionisation stable
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
CP 401 • Ch. de Blandonnet 8
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
CH-1214 Vernier, Geneva
DOCUMENTATION.
Phone: [phone]
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: [e-mail]
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/DTS 6737:2023(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
  © ISO 2023 – All rights reserved
NATIONAL REGULATIONS. © ISO 2023

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ISO/DTS 6737:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.2
5 General description of the design . 2
5.1 Components . 2
5.2 Mode of operation . 3
6 Specifications of the ionisation vacuum gauge. 4
6.1 General specifications and requirements for the gauge head . 4
6.2 Electrical equipment . 5
7 Dimensions and potentials .6
7.1 General . 6
7.2 Dimensions and tolerances . . . 7
7.3 Potentials . 9
7.4 Cathode . . 9
7.5 Anode cage . 9
7.6 Gaps between electrodes . 10
7.7 Electrode materials . 10
7.8 Electrical feedthroughs . 10
7.9 Surrounding tube (envelope) and flanges . 10
7.10 Magnetic fields . 10
8 Characteristics of the gauge (informative) .11
8.1 Sensitivity . 11
8.2 Linearity . 11
8.3 Electron transmission efficiency . 11
8.4 Residual current and resolution . 11
8.5 Repeatability . 11
8.6 Reproducibility .12
8.7 Interference .12
8.8 Temperature of electrodes . 12
8.9 Environmental conditions . 12
9 Handling of and measurement with the gauge .12
9.1 Orientation of the gauge head .12
9.2 Environmental conditions . 12
9.3 Conditioning of the gauge .12
9.4 Testing .12
9.5 Warm­up time . 13
9.6 Sensitivity and calibration . 13
9.7 Measurement . 13
9.8 Transport .13
9.9 Cathode exchange . 13
Annex A (Informative) Electron and ion trajectories of recommended gauge dimensions
according to simulation .14
Bibliography .15
iii
© ISO 2023 – All rights reserved

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ISO/DTS 6737:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non­governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 112, Vacuum technology.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
  © ISO 2023 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/DTS 6737:2023(E)
Introduction
The ionisation vacuum gauge is the only vacuum gauge type in the full range of high and ultrahigh
[1]
vacuum. Important applications need better accuracy, reproducibility and known sensitivities for
many gas species, properties which all current types of ionisation vacuum gauges lack. This document
provides the characteristics for a stable ionisation vacuum gauge so that this gauge is accurate, robust
and long-term stable, with known sensitivity for nitrogen and known relative sensitivity factors, and
can be built by any experienced manufacturer of other ionisation vacuum gauges.
v
© ISO 2023 – All rights reserved

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TECHNICAL SPECIFICATION ISO/DTS 6737:2023(E)
Vacuum technology — Vacuum gauges — Characteristics
for a stable ionisation vacuum gauge
1 Scope
This document describes a special design of an ionisation vacuum gauge which has a well-defined
[2]
ionising electron path length. Due to the construction design, it leads to good measurement accuracy,
long-term stability, as well as gauge independent and reproducible sensitivity for nitrogen and relative
[3] ­6 ­2
sensitivity factors It is designed for the measurement range of 10 Pa to 10 Pa.
This document describes only those dimensions and potentials of the gauge head which are relevant for
the electron and ion trajectories. This document does not describe the electrical components necessary
to operate the ionisation vacuum gauge in detail. The gauge head can be operated by voltage and power
sources and ammeters commercially available, but also by a controller specially built for the purpose of
the operation of this gauge head.
The ionisation vacuum gauge described in this document can be built by any experienced manufacturer
of other ionisation vacuum gauges. It is not subject to intellectual property protection.
It is assumed for this document that the applicant is familiar with both the physics and principles of
ionisation vacuum gauges as well as high and ultra-high vacuum technology in general.
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 13920, Welding - General tolerances for welded constructions - Dimensions for lengths and angles -
Shape and position (ISO 13920:1996)
ISO 2768­1, General tolerances — Part 1: Tolerances for linear and angular dimensions without individual
tolerance indications
ISO 3669, Vacuum technology — Dimensions of knife-edge flanges
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
Wehnelt electrode
Wehnelt
an electrode with cylindrical symmetry around the electron emitting cathode, mainly used for focusing
of the electron beam
1
© ISO 2023 – All rights reserved

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ISO/DTS 6737:2023(E)
3.2
ionisation space
the space in which ions generated by collision of gas molecules with high energy electrons reach the ion
collector by means of a suitable electrostatic field
3.3
Faraday cup
metal cup or other piece of metal designed to catch charged particles in vacuum
Note 1 to entry: In the ionisation vacuum gauge described in this document, the Faraday cup is designed to
capture the electrons emitted from the cathode
3.4
envelope
the metallic wall at zero (earth) potential surrounding the gauge head at least in its full length
3.5
electron transmission
the ratio of electron current measured at the Faraday cup divided by the electron current emitted from
the cathode
4 Symbols and abbreviated terms
I ion current at pressure p [A]
I ion current at residual pressure p [A]
0 0
I electron emission current [A]
e
p pressure [Pa]
p residual pressure [Pa]
0
[1]
r relative sensitivity factor as defined in ISO 27894
x
S sensitivity (coefficient) [1/Pa]
S sensitivity for nitrogen [1/Pa]
N2
5 General description of the design
5.1 Components
The ionisation vacuum gauge consists of the following functional parts:
a) electron emitting cathode,
b) Wehnelt electrode,
c) anode cage in two parts,
d) ion collector,
e) electron deflector,
f) Faraday cup,
g) envelope.
The functional components a) to f) need to be exactly dimensioned.
In addition, the gauge needs electrical feedthroughs, wires, mounting parts and insulators. The gauge
shall be mounted on a DN40CF or on a DN63CF flange according to ISO 3669: with corresponding tube
sizes DN40 or DN63 as envelope.
2
  © ISO 2023 – All rights reserved

---------------------- Page: 7 ----------------------
ISO/DTS 6737:2023(E)
5.2 Mode of operation
A schematic for the illustration of the operation of the gauge is shown in Figure 1, for a detailed drawing
see Figure 2 in 7.2. For simplification, in Figure 1 the anode cage (3) is not been divided in two parts as
in Figure 2 with (3a) and (3b) and the collector ring (6) in between.
Key
1 cathode with emitter disk (red)
2 Wehnelt cylinder
3 anode cage
4 electron deflector
5 faraday cup
6 ion collector
+
I ion
-
e electron
Figure 1 — Illustration of mode of operation (informative)
Electrons are emitted from the hot thermionic cathode (1 in Figure 1 and Figure 2), which is preferably
an indirectly heated disk emitter on a potential of 50 V. The Wehnelt electrode (2 in Figure 1)
surrounding the cathode has a lower potential and controls and focuses the electron beam into the
opening of the anode cage at 250 V.
Note that in the future, it can be possible that the thermionic cathode can be replaced by a so-called
cold field emission cathode. This cathode shall be long-term stable and provide an electron current of
about 100 µA. In addition, it shall be ensured that the energy of the electrons along their path is not
changed compared to the design with thermionic cathode.
Due to the penetration of the anode potential into that of the Wehnelt electrode the electrons can be
extracted and accelerated into the inner part of the cylindrical anode cage. The first part of the anode
cage (3a at 250 V, see Figure 2), the ion collector ring (0 V, 6 in Figure 1 and Figure 2) and the second
remaining part of the anode cage (250 V, 3b in Figure 2) form an electrostatic lens which focuses the
electron beam into the circular exit of the anode cage. Behind this exit the electron beam is deflected
by the electron deflector electrode (45 V, 4 in Figure 1 and Figure 2) in a U­turn onto the capturing part
of the Faraday cup (280 V, 5 in Figure 1 and Figure 2). When the electrons hit the Faraday cup, they will
generate X-rays. By the U-turn, it is ensured that these X-rays have a very low probability to reach the
ion collector or the anode where they would generate secondary electrons.
The ions generated by the electron beam inside the anode cage are accelerated towards the ion collector
which consists of the mentioned ring and a rod reaching into the larger space of the anode cage. Ions
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ISO/DTS 6737:2023(E)
generated behind the exit of the cage are accelerated towards the electron deflector electrode. The
ionisation space is well defined in this design.
The measured ion current will be proportional to the gas density in contact with the electron beam,
the ionisation probability of the gas molecules by the electron impacts along their path, the mean path
length of the electrons inside the ionisation space and the electron current.
Due to the focused electron beam inside the anode cage, the electron current should not exceed 200 µA.
Higher currents can cause non­linearities.
The mean electron path length is defined by the length of the anode cage and the potential inside it. Any
changes of the emission points of the electrons on the cathode will not significantly change the path
length. A replacement of the same cathode type will have an insignificant influence on the path length.
Space charge effects of ions will also have an insignificant influence on the path length within the
specified measurement range up to 0,01 Pa. Due to the well-defined electron path length, the nitrogen
sensitivity and the relative sensitivity factors will not significantly vary from gauge to gauge except
within the uncertainty due to variation of secondary electrons produced by the ion impingement on the
[4]
collector
As for an ionisation vacuum gauge of the extractor type, in this gauge, X-rays have a low probability
of reaching the ion collector. This ensures that the secondary electron current on the ion collector
produced by X-rays is rather small. Such a current would be indistinguishable from the measured ion
current.
Ions desorbed by electron impact in the Faraday cup will be attracted to the electron deflector and will
not reach the ion collector. Electron stimulated desorption of neutrals, however, will contribute to the
gas density in the gauge and therefore to the ion current.
6 Specifications of the ionisation vacuum gauge
6.1 General specifications and requirements for the gauge head
a) The electrons shall have a direct and well-defined path from their source, the cathode, through
the ionisation space to the target, the Faraday cup. The path length shall not be increased by
oscillations through the ionisation space, e.g. by a magnetic field.
b) The two parts of the anode cage, the ion collector ring and the Wehnelt electrode shall have a
common cylindrical axis according to best possible practice. The center of the cathode shall be
aligned to this axis.
c) The electron emitting cathode shall be surrounded by a Wehnelt electrode.
d) It is recommended that the cathode is an indirectly heated disk emitter to ensure well defined and
stable starting points on equal potential of the electron trajectories over the emission area.
e) The shape, dimensions, position and potentials of the anode cage, Wehnelt electrode and electron
emitting part of the cathode shall be such that the emitted electrons are accelerated parallel to or
with a small maximum angle (typically < 5°) to the cylindrical axis described in b).
f) The two parts of the anode cage and the ion collector ring shall form an electrostatic lens for the
electrons to focus them to the circular exit of the anode cage. The electron beam shall be focused
in such a way that less than 5 % of the total electron current hits the anode cage. The collector
electrode consists of a ring with a long rod reaching into the anode cage in the direction of the
Faraday cup.
g) It is necessary that openings in the cylindrical anode cage allow a free exchange of molecules inside
and outside of the cage so that there is no significant difference in gas density. This can be achieved
by slotted holes or similar. It is, however, required that there is no significant potential penetration
from the envelope into the anode cage.
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ISO/DTS 6737:2023(E)
h) The electron beam shall be captured by a Faraday cup located behind the exit of the anode cage.
The area of impact of the electrons shall be located such that generated X-rays have no direct line of
sight to the ion collector. This is achieved by a deflector electrode which directs the electron beam
onto a suitable target spot of the Faraday cup.
i) The electrical insulation of the ion collector to the anode cage parts shall have a total resistance
(surface and bulk) such that the leakage current across them contributes with less than 0,4 % to
­6
the measured ion current at 10 Pa of nitrogen.
NOTE 1 With dimensions and potentials described in Clause 7, at 30 µA emission current, the collector
­6
current amounts to 10 pA at 10 Pa of nitrogen, so that 0,4 % correspond to 40 fA. To achieve this, a guard
electrode is helpful.
j) The attachment of the gauge electrodes shall be such that their positions against each other are
not changed during a transport of the gauge. Also, the stiffness of the electrodes shall be such that
their shape is not changed during transport. Before and after a test according to ISTA 2A:2011,
the sensitivity for nitrogen near 1 mPa is to be reproduced within 2 % (k = 2 according to GUM:
ISO/IEC Guide 98­1). The test should be performed 3 times or more.
NOTE 2 It is sufficient to perform the ISTA 2A:2011 test with a single gauge after development of a
prototype by a manufacturer.
k) The envelope shall be a cylindrical tube as for UHV components and cover the full length of the
gauge parts plus 10 mm in length in both directions. It is recommended to close the cylinder with a
grid or similar as equipotential plane. It is recommended to attach two CF flanges at the ends of the
envelope tube.
l) The whole gauge head shall withstand bake-out temperatures of at least 250 °C.
m) No ferromagnetic material should be used in the gauge head except for feedthroughs (see 7.8) and
the envelope (see 7.9).
All the specifications above are met by the mandatory and recommended dimensions and potentials
described in Clause 7.
6.2 Electrical equipment
The voltage output of the power supplies must supply voltages between 25 V and 300 V. The cathode,
Wehnelt and deflector voltages shall be stable within ±0,2 V, anode and Faraday voltages within ±0,4 V.
The power supply for the heating current of the thermionic cathode shall be on high potential of 50 V
and provide enough heating power for the cathode in use to provide an emission current of up to 200 µA.
It is recommended that the total emission current (on anode and Faraday cup) be either measured with
a standard uncertainty of 0,3 % or controlled within a standard uncertainty of 0,3 %.
NOTE 1 Due to some misalignment or scattering, a small, but unwanted part of electrons can reach the anode.
These electrons and secondary electrons can also ionise gas molecules and contribute to the ion current.
Also, it is recommended that the current from collector to ground is measured with a standard
­6 ­2
uncertainty of 0,3% in the range of nitrogen pressure from 10 Pa to 10 Pa.
NOTE 2 With dimensions and potentials described in 7, at 30 µA emission current, the collector current ranges
from about 10 pA to 100 nA.
It is permissible to use current measuring instruments with higher uncertainties. To the extent of their
higher uncertainties, this will increase the uncertainty of pressure measurement. If either or both
currents are measured with a standard uncertainty of more than 2 %, the uncertainty of nitrogen
sensitivity and relative gas sensitivity factors given in 8.1 is exceeded for some gas species and an
individual calibration of the gauge can be necessary (see also 9.6).
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ISO/DTS 6737:2023(E)
Electrical feedthroughs, connectors and cables shall be applied:
— by which the range and the uncertainties of current measurements and
— by which the necessary power and potential requirements,
given in this document can be achieved.
7 Dimensions and potentials
7.1 General
The following dimensions and potentials meet the specifications given in 6.1 and are mandatory if
not specified otherwise. Tolerances, gaps and angles where critical are given in Table 1. For all other
dimensions machining tolerances of class "m" or "f" ac
...