Medical electrical equipment - Dosimetric instruments used for non-invasive measurement of X-ray tube voltage in diagnostic radiology

Specifies the performance requirements of instruments as used in the non-invasive measurement of X-ray tube voltage up to 150 kV and the relevant compliance tests. Describes the method for calibration and gives guidance for estimating the uncertainty in measurements performed under conditions different from those during calibration. This standard is not concerned with the safety aspect of such instruments. The requirements for electrical safety applying to them are contained in IEC 61010-1. This consolidated version consists of the first edition (2002) and its amendment 1 (2008). Therefore, no need to order amendment in addition to this publication.

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Status
Published
Publication Date
25-Jan-2009
Current Stage
PPUB - Publication issued
Start Date
26-Jan-2009
Completion Date
26-Jan-2009
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IEC 61676
Edition 1.1 2009-01
INTERNATIONAL
STANDARD
Medical electrical equipment – Dosimetric instruments used for non-invasive
measurement of X-ray tube voltage in diagnostic radiology
IEC 61676:2002+A1:2008
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61676
Edition 1.1 2009-01
INTERNATIONAL
STANDARD
Medical electrical equipment – Dosimetric instruments used for non-invasive
measurement of X-ray tube voltage in diagnostic radiology
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
ICS 11.040.50; 11.040.55 ISBN 978-2-88910-552-6
® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – 61676 © IEC:2002+A1:2008(E)
CONTENTS

FOREWORD...........................................................................................................................3

INTRODUCTION.....................................................................................................................5

1 Scope and object..............................................................................................................6

2 Normative references.......................................................................................................6

3 Terminology and definitions..............................................................................................7

4 General performance requirements for measurement of PRACTICAL PEAK VOLTAGE

measurements................................................................................................................10

4.1 Quantity to be measured .......................................................................................10

4.2 Limits of PERFORMANCE CHARACTERISTICs ...............................................................10

4.3 LIMITS OF VARIATION for effects of INFLUENCE QUANTITIES.........................................13

4.4 Performance test procedures.................................................................................15

5 Special instrumental requirements and marking..............................................................22

5.1 Requirements for the complete instruments...........................................................22

5.2 General.................................................................................................................22

5.3 Display..................................................................................................................22

5.4 Range of measurement .........................................................................................22

5.5 Connectors and cables..........................................................................................22

6 ACCOMPANYING DOCUMENTS.............................................................................................23

6.1 General.................................................................................................................23

6.2 Information provided..............................................................................................23

6.3 Instrument description...........................................................................................23

6.4 Detector................................................................................................................23

6.5 Delay time.............................................................................................................23

6.6 Measurement window............................................................................................23

6.7 Data outlet............................................................................................................23

6.8 Transport and storage...........................................................................................23

Annex A (informative) Recommended performance criteria for the invasive divider ..............24

Annex B (informative) Additional information on PRACTICAL PEAK VOLTAGE ............................25

Annex C (informative) Glossary of defined terms .................................................................32

---------------------- Page: 4 ----------------------
61676 © IEC:2002+A1:2008 (E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
⎯⎯⎯⎯⎯
MEDICAL ELECTRICAL EQUIPMENT –
Dosimetric instruments used for non-invasive measurement
of X-ray tube voltage in diagnostic radiology
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any

equipment declared to be in conformity with an IEC Publication.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 61676 has been prepared by subcommittee SC 62C: Equipment

for radiotherapy, nuclear medicine and radiation dosimetry, of IEC Technical Committee 62:

Electrical equipment in medical practice.

This consolidated version of IEC 61676 consists of the first edition (2002) [documents

62C/340/FDIS and 62C/344/RVD] and its amendment 1 (2008) [documents 62C/445/CDV and

62C/452/RVC].

The technical content is therefore identical to the base edition and its amendment and has

been prepared for user convenience.
It bears the edition number 1.1.

A vertical line in the margin shows where the base publication has been modified by

amendment 1.

NOTE In the amendment, a new influence quantity “Additional tungsten filtration (tube aging)” has been

introduced.
---------------------- Page: 5 ----------------------
– 4 – 61676 © IEC:2002+A1:2008(E)
Annexes A, B and C are for information only.
In this standard the following print types are used:

− requirements, compliance with which can be tested, and definitions: in roman type;

− notes, explanations, advice, general statements and exceptions: in small roman type;

− test specifications: in italic type;

− TERMS USED THROUGHOUT THIS STANDARD THAT HAVE BEEN DEFINED IN CLAUSE 3 OR IN IEC

60601-1 AND ITS COLLATERAL STANDARDS: IN SMALL CAPITALS.

The committee has decided that the contents of the base publication and its amendments will

remain unchanged until the maintenance result date indicated on the IEC web site under

"http://webstore.iec.ch" in the data related to the specific publication. At this date,

the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

NOTE The committee is aware of the fact that this standard does not address all problems associated with non-

invasive high voltage measurements. In particular one influence quantity concerning the target condition is not

dealt with at all. Before this can be done, a substantial amount of measurements is still necessary to improve the

physical understanding of this influence quantity. On the other hand, for the reasons described in the introduction

there is an urgent need to publish this standard in order to assure that non-invasive measurements are comparable

to each other within tolerable uncertainties, regardless of differences in X-RAY GENERATOR, waveform or other

influence quantities (except target condition), which is not the case for the time being. The committee has decided

to revise this standard as soon as sufficient knowledge on the outstanding items is available.

---------------------- Page: 6 ----------------------
61676 © IEC:2002+A1:2008 (E) – 5 –
INTRODUCTION

The result of a measurement of the X-RAY TUBE VOLTAGE by means of invasive or non-invasive

instruments is normally expressed in the form of one single number for the value of the tube

voltage, irrespective of whether the tube voltage is constant potential or shows a time

dependent waveform. Non-invasive instruments for the measurement of the X-RAY TUBE

VOLTAGE on the market usually indicate the ‘mean peak voltage’. But the quantity ‘mean peak

voltage’ is not unambiguously defined and may be any mean of all voltage peaks. It is

impossible to establish test procedures for the performance requirements of non-invasive

instruments for the measurement of the X-RAY TUBE VOLTAGE without the definition of the

quantity under consideration. Therefore, this Standard is based on a quantity recently

proposed in the literature to be called "PRACTICAL PEAK VOLTAGE". The PRACTICAL PEAK

VOLTAGE is unambiguously defined and applicable to any waveform. This quantity is related to

the spectral distribution of the emitted X-RADIATION and the image properties. X-RAY

GENERATORS operating at the same value of the PRACTICAL PEAK VOLTAGE will produce the

same low level contrast in the RADIOGRAMS, even when the waveforms of the tube voltages

are different. Detailed information on this concept is provided in Annex B. An example for the

calculation of the PRACTICAL PEAK VOLTAGE in the case of a “falling load” waveform is also

given in Annex B.

As a result of introducing a new quantity, the problem arises that this standard has been

written for instruments which were not explicitly designed for the measurement of the

PRACTICAL PEAK VOLTAGE. However, from preliminary results of a trial type test of a non-

invasive instrument currently on the market, it can be expected that future instruments and

most instruments on the market will be able to fulfil the requirements stated in this standard

without insurmountable difficulties. For the most critical requirements on voltage waveform

and frequency dependence of the RESPONSE, it turned out from these investigations that it is

even easier to comply with the standard by using the PRACTICAL PEAK VOLTAGE as the

measurement quantity.

The calibration and adjustment of the X-RAY TUBE VOLTAGE of an X-RAY GENERATOR is generally

performed by the MANUFACTURER using a direct INVASIVE MEASUREMENT. Instruments utilising

NON-INVASIVE MEASUREMENTS can also be used to check the calibration or to adjust THE X-RAY

TUBE VOLTAGE. These instruments are required to have uncertainties of the voltage

measurement comparable with the INVASIVE MEASUREMENT. One of the most important

parameters of diagnostic X-RAY EQUIPMENT is the voltage applied to the X-RAY TUBE, because

both the image quality in diagnostic radiology and the DOSE received by the PATIENT

undergoing radiological examinations are dependent on the X-RAY TUBE VOLTAGE. An overall

uncertainty below ±5 % is required, and this value serves as a guide for the LIMITS OF

VARIATION for the effects of INFLUENCE QUANTITIES.
———————
See annex B.
---------------------- Page: 7 ----------------------
– 6 – 61676 © IEC:2002+A1:2008(E)
MEDICAL ELECTRICAL EQUIPMENT –
Dosimetric instruments used for non-invasive measurement
of X-ray tube voltage in diagnostic radiology
1 Scope and object

This International Standard specifies the performance requirements of instruments as used in

NON-INVASIVE MEASUREMENT of X-RAY TUBE VOLTAGE up to 150 kV and the relevant
the

compliance tests. This standard also describes the method for calibration and gives guidance

for estimating the uncertainty in measurements performed under conditions different from

those during calibration.
Applications for such measurement are found in diagnostic RADIOLOGY including

mammography, COMPUTED TOMOGRAPHY (CT), dental radiology and RADIOSCOPY. This standard

is not concerned with the safety aspect of such instruments. The requirements for electrical

safety applying to them are contained in IEC 61010-1.
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.
IEC 60417 (all parts), Graphical symbols for use on equipment
IEC 60788:1984, Medical radiology – Terminology

IEC 61000-4-2:1995, Electromagnetic compatibility (EMC) – Part 4: Testing and measurement

techniques – Section 2: Electrostatic discharge immunity test. Basic EMC Publication

IEC 61000-4-3:2000, Electromagnetic compatibility (EMC) – Part 4-3: Testing and measure-

ment techniques – Radiated, radio-frequency, electromagnetic field immunity test. Basic EMC

Publication

IEC 61000-4-4:1995, Electromagnetic compatibility (EMC) – Part 4: Testing and measurement

techniques – Section 4: Electrical fast transient/burst immunity test. Basic EMC Publication

IEC 61000-4-5:1995, Electromagnetic compatibility (EMC) – Part 4: Testing and measurement

techniques – Section 5: Surge immunity test. Basic EMC Publication

IEC 61000-4-6:1996, Electromagnetic compatibility (EMC) – Part 4: Testing and measurement

techniques – Section 6: Immunity to conducted disturbances, induced by radio frequency

fields. Basic EMC Publication

IEC 61000-4-11:1994, Electromagnetic compatibility (EMC) – Part 4: Testing and measure-

ment techniques – Section 11: Voltage dips, short interruptions and voltage variations

immunity tests. Basic EMC Publication

IEC 61010-1:2001, Safety requirements for electrical equipment for measurement, control,

and laboratory use – Part 1:General Requirements
IEC 61187:1993, Electrical and electronic measuring equipment – Documentation
---------------------- Page: 8 ----------------------
61676 © IEC:2002+A1:2008 (E) – 7 –
ISO:1993, International vocabulary of basic and general terms in metrology
(ISBN 92-67-01075-1)
ISO 7000:1989, Graphical symbols for use on equipment – Index and synopsis
3 Terminology and definitions
For the purposes of this standard the following definitions apply.

The definitions given in this standard are generally in agreement with those in IEC 60788 and

the ISO International vocabulary of basic and general terms in metrology. Any terms not

defined in this subclause have the meanings defined in the above publications or are

assumed to be in general scientific usage.
3.1
CORRECTION FACTOR

dimensionless multiplier which corrects the INDICATED VALUE of an instrument from its value

when operated under particular conditions to its value when operated under stated REFERENCE

CONDITIONS
3.2
EFFECTIVE RANGE

range of INDICATED VALUES for which an instrument complies with a stated performance. The

maximum (minimum) effective INDICATED VALUE is the highest (lowest) in this range

3.3
INDICATED VALUE

the value of quantity derived from the scale reading of an instrument together with any scale

factors indicated on the control panel of the instrument
3.4
INFLUENCE QUANTITY

any external quantity that may affect the performance of an instrument (e.g. ambient

temperature etc.) and any property of the X-RAY EQUIPMENT under test that needs to be taken

into account in using the instrument for NON-INVASIVE MEASUREMENT of X-RAY TUBE VOLTAGE

(e.g. range of X-RAY TUBE VOLTAGE, ANODE ANGLE, anode material, TOTAL FILTRATION etc.)

3.5
INSTRUMENT PARAMETER

any internal property of an instrument that may affect the performance of the instrument

3.6
INTRINSIC ERROR

deviation of the MEASURED VALUE (i.e. the INDICATED VALUE, corrected to REFERENCE

CONDITIONS) from the CONVENTIONAL TRUE VALUE under STANDARD TEST CONDITIONS
3.7
INVASIVE MEASUREMENT

measurement of the X-RAY TUBE VOLTAGE by external connection of a suitable meter or a high

resistance divider
3.8
LIMITS OF VARIATION

the maximum VARIATION of a PERFORMANCE CHARACTERISTIC y, permitted by this standard. If

the LIMITS OF VARIATION are stated as ±L % the VARIATION Δy / y, expressed as a percentage,

shall remain in the range from −L % to +L %
---------------------- Page: 9 ----------------------
– 8 – 61676 © IEC:2002+A1:2008(E)
3.9
MAXIMUM PEAK VOLTAGE

maximum value of the X-RAY TUBE VOLTAGE in a specified time interval. The unit of this

quantity is the volt (V)
3.10
MEAN PEAK VOLTAGE

mean value of all X-RAY TUBE VOLTAGE peaks during a specified time interval. The unit of this

quantity is the volt (V)
3.11
MEASURED VALUE

the best estimate of the CONVENTIONAL TRUE VALUE of a quantity, being derived from the

INDICATED VALUE of an instrument together with the application of all relevant CORRECTION

FACTORS

NOTE The CONVENTIONAL TRUE VALUE will usually be the value determined by the working standard with which the

instrument under test is being compared
3.12
MINIMUM EFFECTIVE RANGE

the MINIMUM EFFECTIVE RANGE is the smallest permitted range of INDICATED VALUES for which an

instrument complies with a stated performance
3.13
NON-INVASIVE MEASUREMENT
measurement of X-RAY TUBE VOLTAGE by analysis of the emitted RADIATION
3.14
PERFORMANCE CHARACTERISTIC

one of the quantities used to define the performance of an instrument (e.g. RESPONSE)

3.15
VOLTAGE RIPPLE

VOLTAGE RIPPLE at the X-RAY TUBE, r, is expressed as a percentage of the peak voltage,

the
U , over a specified time interval. This is expressed by the equation:
max
U − U
max min
r = ⋅ 100 %
max

where U is the highest voltage in the interval, and U is the lowest voltage in the interval

max min
---------------------- Page: 10 ----------------------
61676 © IEC:2002+A1:2008 (E) – 9 –
3.16
PRACTICAL PEAK VOLTAGE (PPV)
The PRACTICAL PEAK VOLTAGE U is defined as:
max
p(U) ⋅ w(U) ⋅ U dU
max
ˆ min
U = with p(U) dU = 1
max
min
p(U) ⋅ w(U) dU
min

where p(U) is the distribution function for the voltage U and w(U) is a weighting function. U

max

is the highest voltage in the interval, and U is the lowest voltage in the interval. The unit of

min
the quantity PRACTICAL PEAK VOLTAGE is the volt (V)

NOTE Additional information on the PRACTICAL PEAK VOLTAGE, the weighting function w(U) and the distribution

function p(U) is provided in Annex B. Using this weighting function w(U) the PRACTICAL PEAK VOLTAGE will be

defined as the constant potential which produces the same AIR KERMA contrast behind a specified PHANTOM as the

non-dc voltage under test.
3.17
RATED RANGE (of use)

the range of values of an INFLUENCE QUANTITY or INSTRUMENT PARAMETER within which the

instrument will operate within the LIMITS OF VARIATION. Its limits are the maximum and

minimum RATED values.

The MINIMUM RATED RANGE is the least range of an INFLUENCE QUANTITY or INSTRUMENT

PARAMETER within which the instrument shall operate within the specified LIMITS OF VARIATION

in order to comply with this standard
3.18
REFERENCE CONDITIONS

conditions under which all INFLUENCE QUANTITIES and INSTRUMENT PARAMETERS have their

REFERENCE VALUES
3.19
REFERENCE VALUE

particular value of an INFLUENCE QUANTITY (or INSTRUMENT PARAMETER) chosen for the

purposes of reference i.e. the value of an INFLUENCE QUANTITY (or INSTRUMENT PARAMETER) at

which the CORRECTION FACTOR for dependence on that INFLUENCE QUANTITY (or INSTRUMENT

PARAMETER) is unity
3.20
RELATIVE INTRINSIC ERROR
the ratio of the INTRINSIC ERROR to the CONVENTIONAL TRUE VALUE
3.21
RESPONSE
the quotient of the INDICATED VALUE divided by the CONVENTIONAL TRUE VALUE
3.22
STANDARD TEST CONDITIONS

conditions under which all INFLUENCE QUANTITIES and INSTRUMENT PARAMETERS have their

STANDARD TEST VALUES
3.23
STANDARD TEST VALUES

a value, values, or a range of values of an INFLUENCE QUANTITY or INSTRUMENT PARAMETER,

which is/are permitted when carrying out calibrations or tests on another INFLUENCE QUANTITY

or INSTRUMENT PARAMETER
---------------------- Page: 11 ----------------------
– 10 – 61676 © IEC:2002+A1:2008(E)
3.24
VARIATION

The relative difference Δy / y, between the values of a PERFORMANCE CHARACTERISTIC y, when

one INFLUENCE QUANTITY (or INSTRUMENT PARAMETER) assumes successively two specified

values, the other INFLUENCE QUANTITIES (and INSTRUMENT PARAMETERS) being kept constant at

the STANDARD TEST VALUES (unless other values are specified)
3.25
X-RAY TUBE VOLTAGE

potential difference applied to an X-RAY TUBE between the anode and the cathode . The unit of

this quantity is the volt (V)
4 General performance requirements for measurement of PRACTICAL PEAK
VOLTAGE measurements
4.1 Quantity to be measured
The quantity to be measured is the PRACTICAL PEAK VOLTAGE.
NOTE Additional quantities may be displayed.

The MINIMUM EFFECTIVE RANGES of PRACTICAL PEAK VOLTAGE shall be as listed in table 1 for the

relevant X-RAY applications.
Table 1 – MINIMUM EFFECTIVE RANGES
Application Nominal Anode Material MINIMUM EFFECTIVE RANGE
Mammography
a)
24 kV to 35 kV
(20 kV to 50 kV)
Diagnostic
W 60 kV to 120 kV
(40 kV to 150 kV)
W 100 kV to 140 kV
(80 kV to 150 kV)
Dental
W 60 kV to 90 kV
(40 kV to 110 kV)
Fluoroscopic
W 60 kV to 120 kV
(40 kV to 130 kV)

For mammography anode materials other than Mo, the MINIMUM EFFECTIVE RANGE of PPV shall be at least

10 kV.
4.2 Limits of PERFORMANCE CHARACTERISTICs
4.2.1 Limits

All values of the limits of PERFORMANCE CHARACTERISTICS stated in this subclause do not

contain the uncertainty of the test equipment.
4.2.2 Maximum error
4.2.2.1 Maximum RELATIVE INTRINSIC ERROR for voltages above 50 kV

The RELATIVE INTRINSIC ERROR, l, of PRACTICAL PEAK VOLTAGE, U , measurements made under

STANDARD TEST CONDITIONS, shall not be greater than ±2 % over the EFFECTIVE RANGE of

voltages. This is expressed by the equation:
ˆ ˆ
U − U
meas true
I = ≤ 0,02
true
---------------------- Page: 12 ----------------------
61676 © IEC:2002+A1:2008 (E) – 11 –
ˆ ˆ
MEASURED VALUE of PRACTICAL PEAK VOLTAGE and
where U is the U is the true value of
meas true

the PRACTICAL PEAK VOLTAGE. The voltages for the MINIMUM EFFECTIVE RANGE are listed in

table 1.
The compliance test for performance requirement 4.2.2.1 is listed under 4.2.2.2.
4.2.2.2 Maximum INTRINSIC ERROR for voltages below 50 kV

The maximum INTRINSIC ERROR, E, of PRACTICAL PEAK VOLTAGE, U , measurements made under

STANDARD TEST CONDITIONS shall not be greater than ±1 kV over the EFFECTIVE RANGE of

voltages. This is expressed by the equation:
ˆ ˆ
E = U − U ≤ 1,0 kV
meas true
ˆ ˆ
where MEASURED VALUE of PRACTICAL PEAK VOLTAGE and
U is the U is the conventional
meas true

true value of the PRACTICAL PEAK VOLTAGE. The voltages for the MINIMUM EFFECTIVE RANGE are

listed in table 1.
Compliance with performance requirements 4.2.2.1 and 4.2.2.2 shall be checked by

measuring the RELATIVE INTRINSIC ERROR above 50 kV or the INTRINSIC ERROR below 50 kV

over the EFFECTIVE RANGE of voltages for each application claimed. STANDARD TEST CONDITIONS

are listed in table 2 for each application. The end points of the EFFECTIVE RANGE must be

checked. For mammography the nominal step between measurements shall be no greater

than 2 kV. For all other applications the nominal step between measurements shall be no

greater than 5 kV for voltages below 100 kV, and no greater than 10 kV for voltages above

100 kV.

If more than one instrument configuration can be utilised to measure a span of voltages, then

that span of voltages shall be measured utilising all relevant instrument configurations. As a

minimum the end points and enough interim points shall be measured to meet the minimum

step requirements given above. An example could be the use of different absorber pairs to

provide overlapping voltage spans. In the case of different absorber pairs, if the first

measured from 40 kV to 80 kV, and the second from 60 kV to 120 kV, then the overlapping

span would be from 60 kV to 80 kV. At a minimum, measurements would be made utilising

each absorber pair at 60 kV, 65 kV, 70 kV, 75 kV, and 80 kV.
4.2.3 Over and under range indications

The instrument must clearly indicate when it is displaying a reading outside its EFFECTIVE

RANGE of PRACTICAL PEAK VOLTAGE.

Conditions above and below the EFFECTIVE RANGE of PRACTICAL PEAK VOLTAGE shall be tested

and it shall be demonstrated that if the instrument displays a reading it will be clearly

indicated to the user that the reading might not meet the accuracy of the instrument.

If more than one instrument configuration can be utilised to measure a span of voltages, then

over and under range conditions shall be checked for all relevant instrument configurations.

An example could be the use of different absorber pairs to provide overlapping voltage spans.

In the case of different absorber pairs, if the first measured from 40 kV to 80 kV, and the

second from 60 kV to 120 kV, then over and under range indications would be checked below

40 kV and above 80 kV for the first absorber pair, and below 60 kV and above 120 kV for the

second absorber pair. (The instrument’s refusal to make a reading under these conditions is

an acceptable result.)

Compliance with performance requirement 4.2.3 shall be verified at the lowest limit of the

RAT
...

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