IEC 62812:2019

Low resistance measurements - Methods and guidance

IEC 62812:2019 specifies methods of measurement and associated test conditions that eliminate or reduce the influence of adverse phenomena in order to improve the attainable accuracy of low-resistance measurements. The methods described in this document are applicable for the individual measurements of the resistance of individual resistors, and also for resistance measurements as part of a test sequence. They are applied if prescribed by a relevant component specification, or if agreed between a customer and a manufacturer.
The contents of the corrigendum of March 2020 have been included in this copy.

Mesures de faibles résistances - Méthodes et recommandations

L'IEC 62812:2019 spécifie les méthodes de mesure et les conditions d'essai associées qui éliminent ou réduisent l'influence des phénomènes défavorables afin d'améliorer la précision réalisable des mesures de faibles résistances. Les méthodes décrites dans le présent document s'appliquent aux mesures individuelles de la valeur de résistances individuelles, ainsi qu'aux mesures de résistances dans le cadre d'une séquence d'essai. Elles sont appliquées si elles sont prescrites par une spécification de composant pertinente ou si elles font l'objet d'un accord entre un client et un fabricant.
Le contenu du corrigendum de mars 2020 a été pris en considération dans cet exemplaire.

General Information

• Status: Published
• Publication Date: 01-May-2019
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 31.040.01 - Resistors in general
• Technical Committee: TC 40 - Capacitors and resistors for electronic equipment
• Current Stage: PPUB - Publication issued
• Completion Date: 02-May-2019

Standards Content (sample)

IEC 62812
Edition 1.0 2019-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Low resistance measurements – Methods and guidance
Mesures de faibles résistances – Méthodes et recommandations
IEC 62812:2019-05(en-fr)
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IEC 62812
Edition 1.0 2019-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Low resistance measurements – Methods and guidance
Mesures de faibles résistances – Méthodes et recommandations
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.040.01 ISBN 978-2-8322-6870-4

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 62812:2019 © IEC 2019
CONTENTS

FOREWORD ........................................................................................................................... 4

1 Scope .............................................................................................................................. 6

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

3 Terms and definitions ...................................................................................................... 6

4 Resistance measurement phenomena ............................................................................. 7

4.1 General ................................................................................................................... 7

4.2 Lead and contact resistance ................................................................................... 7

4.3 Self-heating ............................................................................................................ 9

4.4 Variation of resistance with temperature ............................................................... 10

4.5 Thermoelectric e.m.f. ............................................................................................ 12

4.6 Peltier effect ......................................................................................................... 15

5 Methods of measurement .............................................................................................. 16

5.1 General ................................................................................................................. 16

5.2 Four-wire resistance measurement ....................................................................... 16

5.3 Offset compensation method ................................................................................. 19

5.4 Current inversion method ...................................................................................... 22

5.5 Differential current inversion method ..................................................................... 25

5.6 Short-term trigger method ..................................................................................... 28

6 Connecting the specimen .............................................................................................. 32

6.1 Resistors with lead wires for soldered assembly ................................................... 32

6.1.1 Connecting leaded resistors in a test fixture .................................................. 32

6.2 Resistors with solder terminations for surface mount assembly ............................. 33

6.2.1 Connecting SMD resistors on a test substrate................................................ 33

6.2.2 Connecting SMD resistors in a test fixture ..................................................... 35

7 Information to be given in the relevant component specification ..................................... 36

Annex A (normative) Letter symbols and abbreviated terms ................................................. 37

A.1 Letter symbols ...................................................................................................... 37

A.2 Abbreviated terms ................................................................................................. 38

Annex B (informative) Test results of soldering pad with Kelvin connection for surface

mount resistors ..................................................................................................................... 39

B.1 General ................................................................................................................. 39

B.2 Test procedures .................................................................................................... 39

B.2.1 Test substrates .............................................................................................. 39

B.2.2 Test method .................................................................................................. 41

B.3 Measurement result and studies ........................................................................... 42

Bibliography .......................................................................................................................... 45

Figure 1 – Resistance measurement using two-wire sensing ................................................... 8

Figure 2 – Variation of resistance with temperature (random example) ................................ 10

Figure 3 – Resistances on a resistor with lead wires ............................................................. 11

Figure 4 – SMD chip resistor on a PCB ................................................................................. 12

Figure 5 – Thermoelectric e.m.f. ........................................................................................... 13

Figure 6 – Thermocouples on a resistor with lead wires ........................................................ 14

Figure 7 – Resistance measurement affected by thermoelectric e.m.f. .................................. 15

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IEC 62812:2019 © IEC 2019 – 3 –

Figure 8 – Four-wire resistance measurement ...................................................................... 17

Figure 9 – Offset compensation method for resistance measurement .................................... 19

Figure 10 – Current and voltage in the offset compensation method ..................................... 20

Figure 11 – Current inversion method for resistance measurement ....................................... 22

Figure 12 – Current and voltage in the current inversion method ........................................... 23

Figure 13 – Current and voltage in the differential current inversion method ........................ 26

Figure 14 – Example of resistor specimen............................................................................. 31

Figure 15 – Connecting leaded resistors in a test fixture ....................................................... 32

Figure 16 – Resistance of cylindrical copper lead wires ........................................................ 33

Figure 17 – Soldering pad of test substrate for Kelvin (four-point) connections .................... 34

Figure 18 – Resistance of PCB conductor tracks with 35 µm copper thickness..................... 35

Figure 19 – Example for connecting SMD resistors on a test fixture ...................................... 36

Figure B.1 – Lengths of soldering pad ................................................................................... 40

Figure B.2 – Position of voltage sense conductor .................................................................. 40

Figure B.3 – Thickness of the solder printing screen and position of sense line ................... 43

Figure B.4 – Position of voltage-sensing line......................................................................... 43

Figure B.5 – Soldering pad length ......................................................................................... 44

Figure B.6 – Recommended soldering pad ............................................................................ 44

Table 1 – Relative Seebeck coefficients of selected metals................................................... 13

Table A.1 – Letter symbols ................................................................................................... 37

Table B.1 – Thickness of solder printing screen ................................................................... 41

Table B.2 – Table of test conditions ...................................................................................... 42

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– 4 – IEC 62812:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LOW RESISTANCE MEASUREMENTS –
METHODS AND GUIDANCE
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

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

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

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

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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 62812 has been prepared by IEC technical committee 40:

Capacitors and resistors for electronic equipment.
The text of this International Standard is based on the following documents:
FDIS Report on voting
40/2665/FDIS 40/2671/RVD

Full information on the voting for the approval of this International Standard can be found in

the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

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IEC 62812:2019 © IEC 2019 – 5 –

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
The contents of the corrigendum of March 2020 have been included in this copy.
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– 6 – IEC 62812:2019 © IEC 2019
LOW RESISTANCE MEASUREMENTS –
METHODS AND GUIDANCE
1 Scope

Resistance measurements are typically compromised by a variety of phenomena, for example

serial resistance in the measurement path, self-heating or non-ohmic properties. Whether the

effect of such phenomena on a resistance measurement is acceptable or not depends on the

magnitude of each effect in comparison to the resistance and to the required accuracy. Hence,

the risk of erroneous resistance measurements increases with decreasing resistance and with

a tightening of the permissible tolerance.

This document specifies methods of measurement and associated test conditions that

eliminate or reduce the influence of adverse phenomena in order to improve the attainable

accuracy of low-resistance measurements.

The methods described in this document are applicable for the individual measurements of

the resistance of individual resistors, and also for resistance measurements as part of a test

sequence. They are applied if prescribed by a relevant component specification, or if agreed

between a customer and a manufacturer.
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.
IEC 60068-1, Environmental testing – Part 1: General and guidance

IEC 60115-1:2008, Fixed resistors for use in electronic equipment – Part 1: Generic

specification

IEC 60294, Measurement of the dimensions of a cylindrical component with axial terminations

3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 60115-1 and the

following apply.
A list of used letter symbols and abbreviated terms is provided in Annex A.

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

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
electromotive force
e.m.f.
difference in potential that gives rise to an electric current
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IEC 62812:2019 © IEC 2019 – 7 –
3.2
thermoelectric e.m.f.

potential difference occurring at the junctions of dissimilar conductors when a temperature

difference exists between the junctions
3.3
low resistance

resistance for which the predictable error when measured with a conventional two-wire

sensing method is significant in comparison to the required precision or to the stated

tolerance
3.4
four-wire sensing
Kelvin sensing
four-terminal sensing
four-point sensing

electrical impedance measuring technique using separate pairs of wires for carrying the

measuring current and for sensing the potential difference in order to eliminate the impedance

contribution of wiring and contact resistances
3.5
two-wire sensing

conventional electrical impedance measuring technique using one pair of wires for carrying

the measuring current and for sensing the potential difference on the same wires
4 Resistance measurement phenomena
4.1 General

The measurement of a low resistance usually relies on the measurement of a low voltage,

which requires a number of precautions against typical detrimental phenomena such as offset

voltages, radio frequency interference, electromagnetic interference, electrical noise, or non-

ohmic contacts. However, these phenomena are not discussed here as they are not
specifically related to the measurement of resistance.

The voltage to be measured increases with an increase of the measuring current, which may

also result in effects which are adverse to the measurement. Such phenomena are discussed

in Clause 4.
4.2 Lead and contact resistance

A conventional method for measuring a resistance is to use a constant current source with a

known (or measured) output current and a voltmeter for measuring the voltage across the

unknown resistor, while the connection is built with a single pair of test leads, as shown in

Figure 1.
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– 8 – IEC 62812:2019 © IEC 2019
I L
U U R
V R x
IEC
Key
CS current source
VM voltmeter, measuring voltage U
R lead resistance, including contact resistance to the specimen
R resistance to be measured
I supply current from current source
I current passing through the voltmeter
I current passing through the unknown resistor
Figure 1 – Resistance measurement using two-wire sensing

In this circuit, the source current I splits up into the current I passing through the path with

0 M

the unknown resistor and the current I passing through the voltmeter, where I depends on

V V
the measured voltage U and the voltmeter's impedance R .
V V
II + I (1)
0 MV
I = (2)

The voltmeter measures the following voltage drop of current I along both lead and contact

resistances R , plus along the unknown resistor R :
L x
U =I ⋅ 2RR+ (3)
( )
VM L x

This leads to the apparent result of the resistance measurement, R′, based on the measured

voltage U and the known sourced current I :
V 0
U I 2RR+
V M Lx
R= = ⋅(2RR+=) (4)
2RR+
I II+
0 MV

With I → 0, which is the case if R >> (2R + R ), the apparent result tends towards:

V V L x
R′= = ⋅( 22RR+=) RR+ (5)
Lx Lx
I I + 0
0 M
This final apparent result still bears the error ∆R of
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IEC 62812:2019 © IEC 2019 – 9 –
ΔR=R−=R 2R (6)

This error will only be negligible if (2R ) << R , where the negligibility depends on the required

L x
accuracy for the measurement of R .

EXAMPLE 1 A 1 m copper wire with a cross section of 0,5 mm has a resistance of 35 mΩ. Using a pair of these

wires for two-wire sensing for measuring a 100 mΩ resistor results in an unacceptable error of 70 %. The current

passing through the voltmeter due to its limited impedance is not likely to gain any significance on the error figure.

EXAMPLE 2 Using the same circuit for measuring a 10 Ω resistor results in 0,7 % error, while first assuming the

current through the voltmeter to be zero. This 0,7 % error may be acceptable if the relative tolerance of the

resistance is given as ±10 %, but not if it is only ±1 %.

Using a voltmeter in this circuit with an impedance of 1 MΩ results in only a −0,001 % additional error, which is not

significant compared to the error caused by the lead wires. If the voltmeter, however, has an impedance of only

10 kΩ, the additional error is −0,1 % and thus may no longer be negligible.

EXAMPLE 3 For a resistor of 1 kΩ, measured as above, even the seemingly small error of only 0,007 % renders

the described circuit useless, if it is a high precision type with, for example, a relative tolerance of ±0,01 %.

Using a voltmeter in this circuit with an impedance of 1 MΩ results in the additional error of −0,1 %. Comparing the

absolute error contributions, this influence is even larger than the error caused by the lead wires.

4.3 Self-heating

The measuring current I passing through the unknown resistor with its resistance R causes

M x
dissipation of the power P
PI ⋅ R (7)
RM x

The dissipation P produces a temperature rise on the unknown resistor, which depends on

the ability of the test assembly or fixture to dissipate heat to the environment, expressed as

the thermal resistance R . The steady-state temperature rise ∆ϑ on the unknown resistor

th R∝
Δϑ R⋅ P (8)
R ∞ th R

which adds to the ambient temperature next to the specimen, ϑ , and thereby leads to the

amb
steady-state temperature ϑ on the unknown resistor of
ϑ ϑ +Δϑ ϑ +⋅R P (9)
R am∞∞b R amb th R

NOTE The heat conduction out of the unknown resistor is considered to be a linear system for the purpose of this

specification. This is based on the general observation that radiation and convection from the body of most low-

power resistors only have a minor share in the total heat dissipation. A more complex consideration can be suitable

for large resistors where radiation and convection from the body's surface prevail over conduction through the

terminals or lead wires.

The temporal rise of the temperature ϑ (t) on the unknown resistor before reaching the

steady state is determined by the thermal time constant τ of the unknown resistor in its test

assembly or fixture:
ϑϑ(te) +Δϑ ⋅−(1 ) (10)
x amb R ∞

Knowledge of the thermal time constant τ is necessary for measurements aiming at the

steady state and for determination of the timing of switched measurements alike.
= =
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– 10 – IEC 62812:2019 © IEC 2019

The raised temperature on the unknown resistor due to self-heating not only affects the

specimen, but also spreads the heat to the test assembly or mounting and affects those parts

of the measurement circuit as well. Therefore, the raised temperature will be root cause of the

variation of resistance with temperature, as discussed in 4.4, and of the thermoelectric e.m.f.,

as discussed in 4.5.

Self-heating is decreased by reducing the measuring current I as much as possible while

still providing the required voltage for a measurement with the desired accuracy. However,

setting the measuring current is not a common feature with resistance meters. Other options

to reduce the self-heating are to activate the measuring current for a short period only, as

discussed in Clause 5, and of course to enhance the heat flow from the specimen and the test

fixture.
4.4 Variation of resistance with temperature

One of the reference conditions prescribed in IEC 60115-1 for measuring the resistance is the

reference temperature of 20 °C. For practical reasons, however, most tests and

measurements are permitted to be executed under standard atmospheric conditions for

testing as defined in IEC 60068-1, which includes a permissible range for the ambient

temperature from 15 °C to 35 °C.

If measured with sufficient accuracy, a resistor measured at 15 °C or at 35 °C will not show

the same resistance as when measured at 20 °C. In fact, there is a variation of resistance

with temperature for almost every type of resistor, which typically does not follow a linear

relationship. The slope and the amount of variation depend substantially on the technology

and manufacturing of the resistor and in some cases also on the actual resistance.

max
ϑ ϑ
min max
20 °C
max
IEC
Key
α temperature coefficient of resistance
ΔR resistance change
Figure 2 – Variation of resistance with temperature
(random example)

As a specification figure for resistors, the limitation of the permissible range for such

resistance variation in a given temperature range is usually given by a pair of symmetrical

linear slopes through the reference point at 20 °C, +α and −α as shown in Figure 2.

max max

The value α is the absolute value of the specified temperature coefficient of resistance, or

max
TCR.

EXAMPLE 1 Thick film chip resistors of 100 mΩ or lower are typically offered with a TCR of 500 ⋅ 10 /K or above.

Measuring the resistance at 35 °C results in a possible deviation of ±0,75 % from the resistance at the reference

temperature 20 °C. Such a deviation may be acceptable if the relative tolerance of the resistance is given as ±10 %,

but not if it is only ±1 %.
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...