IEC 60195:2016

Method of measurement of current noise generated in fixed resistors

IEC 60195:2016 specifies a method of measurement and associated test conditions to assess the "noisiness", or magnitude of current noise, generated in fixed resistors of any given type. The method applies to all classes of fixed resistors. The aim is to provide comparable results for the determination of the suitability of resistors for use in electronic circuits having critical noise requirements. This edition includes the following significant technical changes with respect to the previous edition:
- harmonization of the allocation of isolation resistors RM in the recommended operating conditions given in Table 2;
- correction of erroneous numeric values of the contribution of system noise, f(T - S) in Table 3;
- addition of advice on the prescription of requirements in a relevant component specification;
- addition of a set of recommended measuring conditions for specimens with a rated dissipation of less than 100 mW;
- complete editorial revision.

Méthode pour la mesure du bruit produit en charge par les résistances fixes

L'IEC 60195:2016 spécifie une méthode de mesure et des conditions d'essai associées pour évaluer l'absence de bruit ou l'amplitude du bruit en charge généré dans des résistances fixes d'un type quelconque. La méthode s'applique à toutes les classes de résistances fixes. Elle a pour but de fournir des résultats comparables pour déterminer l'aptitude des résistances utilisées dans des circuits électroniques dont les exigences relatives au bruit sont critiques. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- harmonisation de l'affectation des résistances d'isolement RM dans les conditions de fonctionnement recommandées données dans le Tableau 2;
- correction des valeurs numériques erronées de la contribution du bruit du système, f(T - S) dans le Tableau 3;
- ajout d'un conseil pour prescrire des exigences dans une spécification de composant applicable;
- ajout d'un ensemble de conditions de mesure recommandées pour des spécimens dont la dissipation assignée est inférieure à 100 mW;
- révision éditoriale complète.

General Information

• Status: Published
• Publication Date: 06-Apr-2016
• ICS: 31.040.10 - Fixed resistors
• Technical Committee: TC 40 - Capacitors and resistors for electronic equipment
• Drafting Committee: MT 60195 - TC 40/MT 60195
• Current Stage: PPUB - Publication issued
• Start Date: 07-Apr-2016
• Completion Date: 15-Apr-2016

Overview

IEC 60195:2016 is an international standard published by the International Electrotechnical Commission (IEC) that specifies a precise method for the measurement of current noise generated by fixed resistors. This method applies universally across all classes and types of fixed resistors. The standard aims to deliver reproducible, comparable results essential for determining the suitability of resistors used in electronic circuits where noise performance is critical.

The standard update from the original 1965 edition includes important technical enhancements such as harmonization of isolation resistor allocations, corrected system noise contributions, prescriptive guidance for component specifications, and recommended measuring conditions for resistors with rated dissipation under 100 mW. It also encompasses a comprehensive editorial revision to clarify procedures and requirements.

Key Topics

• Current Noise Measurement
  IEC 60195:2016 focuses on quantifying the "noisiness," or magnitude, of current noise inherent in fixed resistors. This noise primarily arises due to the granular structure of resistive materials and can indicate defects affecting long-term reliability and aging.

• Measurement Methodology
  The standard details the measurement principles, including the design of suitable measurement systems comprising input circuits, isolation resistors, DC sources, band-pass amplifiers, and r.m.s. meters. It also covers calibration techniques and performance verification to ensure measurement accuracy.

• System Noise Evaluation
  Correction and compensation of system noise are critical aspects discussed in the standard. Accurate noise measurement involves isolating the intrinsic noise of the resistor from the background system noise, using defined numeric values and parameters.

• Operating and Test Conditions
  IEC 60195 provides recommended operating conditions to standardize measurements, including those for resistors with low rated dissipation (<100 mW). This consistency helps maintain uniformity in noise assessment across different laboratories and manufacturers.

• Component Specification Guidance
  The standard includes advice on including current noise measurement requirements in component specifications, facilitating clearer communication between manufacturers and customers regarding noise performance expectations.

Applications

• Electronic Circuit Design
  Designers of sensitive electronic equipment rely on IEC 60195:2016 to select fixed resistors with appropriate noise characteristics, ensuring optimal performance in analog signal processing, precision instrumentation, communication devices, and audio systems.

• Quality Assurance and Component Testing
  Manufacturers utilize this standard to assess resistor quality by detecting abnormal noise levels indicative of material defects or aging processes, supporting improved product reliability and adherence to customer specifications.

• Research and Development
  The method aids researchers in evaluating new resistor technologies by providing an internationally accepted framework to compare noise properties, facilitating innovation in low-noise electronic components.

• Standardization and Compliance
  IEC 60195:2016 serves as a reference for conformity assessment and certification bodies involved in verifying resistor noise performance according to agreed international norms.

Related Standards

• IEC 60068-1:2013 - Environmental Testing – Part 1: General and Guidance
  This standard is normatively referenced in IEC 60195:2016 to establish the environmental test conditions relevant to noise measurement setups and procedures.

• Other IEC Resistor and Noise Standards
  While IEC 60195 addresses current noise measurement in fixed resistors, users may also consider related IEC standards on resistor construction, electrical performance, and reliability testing to ensure a holistic approach to component evaluation.

---

By adopting IEC 60195:2016, professionals in electronics and manufacturing sectors gain access to a rigorously defined and internationally standardized measurement method. This enables enhanced decision-making when selecting fixed resistors for low-noise, high-precision applications, ultimately improving electronic device performance and reliability.

Standards Content (Sample)

IEC 60195 ®
Edition 2.0 2016-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Method of measurement of current noise generated in fixed resistors

Méthode pour la mesure du bruit produit en charge par les résistances fixes

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IEC 60195 ®
Edition 2.0 2016-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Method of measurement of current noise generated in fixed resistors

Méthode pour la mesure du bruit produit en charge par les résistances fixes

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.040.10 ISBN 978-2-8322-3272-9

– 2 – IEC 60195:2016  IEC 2016
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references. 6
3 Terms and definitions . 6
4 Method of measurement . 7
4.1 Noise basics . 7
4.1.1 Noise . 7
4.1.2 Thermal noise . 8
4.1.3 Current noise . 8
4.2 Measurement principle . 9
4.3 Measurement system . 10
4.3.1 Proposal of a suitable measuring system . 10
4.3.2 Alternative measuring systems . 11
4.4 Measurement system requirements . 11
4.4.1 Input circuit . 11
4.4.2 Isolation resistor R . 12
M
4.4.3 DC voltage source . 12
4.4.4 DC electronic voltmeter . 12
4.4.5 Calibration resistor R . 12
Cal
4.4.6 Calibration source . 13
4.4.7 Determination of the calibration voltage . 13
4.4.8 AC band-pass amplifier . 15
4.4.9 AC r.m.s. meter . 16
4.4.10 Test fixture . 16
4.5 Verification of the measuring system . 17
4.5.1 Performance check by measurement of instrument and thermal noise . 17
4.5.2 Performance check by comparison of repeated measurements . 17
5 Measurement procedure . 18
5.1 Ambient conditions . 18
5.2 Preparation of specimen . 18
5.3 Procedure . 18
5.3.1 General . 18
5.3.2 Calibration . 18
5.3.3 Measurement of system noise S . 18
5.3.4 Measurement of total noise T . 19
5.4 Precautions . 22
6 Evaluation of measurement results . 22
6.1 Term for the contribution of system noise . 22
6.2 Determination of the current-noise index A . 24
6.3 Determination of the current-noise voltage ratio CNR . 25
U
6.4 Accuracy . 26
6.5 Requirements . 26
7 Information to be given in the relevant component specification . 26
Annex A (informative) Letter symbols and abbreviations . 27
A.1 Letter symbols . 27

A.2 Abbreviations . 27
Annex X (informative) Cross-reference for references to the prior revision of this
standard . 28
Bibliography . 29

Figure 1 – Block schematic of a suitable measuring system . 11
Figure 2 – Typical transfer function of the band-pass amplifier . 16
Figure 3 – Contribution of system noise, f(T – S) . 23

Table 1 – Permissible limits of system noise . 17
Table 2 – Recommended operating conditions (1 of 2) . 20
Table 3 – Numeric values of the contribution of system noise, f(T – S) . 24
st
Table X.1 – Cross reference for references to the 1 edition of this standard . 28

– 4 – IEC 60195:2016  IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
METHOD OF MEASUREMENT OF CURRENT
NOISE GENERATED IN FIXED RESISTORS

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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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 60195 has been prepared by IEC technical committee 40:
Capacitors and resistors for electronic equipment.
This second edition cancels and replaces the first edition published in 1965 and constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• harmonization of the allocation of isolation resistors R in the recommended operating
M
conditions given in Table 2;
• correction of erroneous numeric values of the contribution of system noise, f(T − S) in
Table 3;
• addition of advice on the prescription of requirements in a relevant component
specification;
• addition of a set of recommended measuring conditions for specimens with a rated
dissipation of less than 100 mW;

• complete editorial revision.
The text of this standard is based on the following documents:
FDIS Report on voting
40/2431/FDIS 40/2458/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website 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.
– 6 – IEC 60195:2016  IEC 2016
METHOD OF MEASUREMENT OF CURRENT
NOISE GENERATED IN FIXED RESISTORS

1 Scope
This International Standard specifies a method of measurement and associated test
conditions to assess the "noisiness", or magnitude of current noise, generated in fixed
resistors of any given type. The method applies to all classes of fixed resistors. The aim is to
provide comparable results for the determination of the suitability of resistors for use in
electronic circuits having critical noise requirements.
The current noise in resistive materials reflects the granular structure of the resistive material.
For some resistor technologies utilizing homogenous layers it is regarded as providing an
indication of defects, which are considered as a root cause for abnormal ageing of the
component under the influence of temperature and time.
The method described in this International Standard is not a general specification requirement
and therefore is applied if prescribed by a relevant component specification, or, if agreed
between a customer and a manufacturer.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60068-1:2013, Environmental testing – Part 1: General and guidance
3 Terms and definitions
For the purposes of this document the following terms and definitions apply.
3.1
current-noise
combination of all random fluctuations of current flow in a resistor which are not attributed to
thermal agitation of the charge carriers (thermal noise) and which depend on the applied
direct current
3.2
current-noise index
A
logarithmic index of the ratio of the open circuit r.m.s. current-noise voltage in a frequency
decade, in µV, over the d.c. voltage applied under test, in V, used to express the “noisiness”
of an individual resistor
Note 1 to entry: The current-noise index is expressed in dB. The ratio between µV and V is not considered in this
index, leading to its value being 120 dB less than the mathematical current-noise index A ′. This practical index
follows the history of prior revisions of this method.

3.3
mathematical current-noise index
A ′
logarithmic index of the ratio of the open circuit r.m.s. current-noise voltage in a frequency
decade over the d.c. voltage applied under test, established in consistent units and their
multiples
Note 1 to entry: The mathematical current-noise index is expressed in dB. This index has been introduced for the
mathematical derivation of the considered parameters.
3.4
current-noise voltage ratio
CNR
U
ratio of the open circuit r.m.s. current-noise voltage in a frequency decade over the d.c.
voltage applied under test, established in µV/V, used to express the “noisiness” of an
individual resistor
3.5
flicker noise
pink noise
random fluctuation present in most electronic devices and typically related to internal
properties of the respective device, which depends on direct current and has a power spectral
density inversely proportional to the frequency
3.6
noise
random fluctuation in an electrical signal having instantaneous amplitude values which, due to
their distribution in a random manner, can only be predicted in terms of probability statements
3.7
shot noise
random fluctuation in electric current due to the flowing current consisting of discrete charges,
which is independent of temperature and has nearly constant power spectral density
throughout the frequency spectrum
3.8
thermal noise
random fluctuation generated by the thermal agitation of the charge carriers (usually the
electrons) inside an electrical conductor at equilibrium, which is independent of any applied
voltage and has nearly constant power spectral density throughout the frequency spectrum
Note 1 to entry: Thermal noise is also referred to as Johnson noise or as Nyquist noise.
4 Method of measurement
4.1 Noise basics
4.1.1 Noise
Noise appears as a spontaneous fluctuating voltage e (t) with instantaneous amplitude
n
values.
Noise voltage is a statistically independent random variable, where for most kinds of noise the
frequency distribution of amplitudes follows a Gaussian distribution curve. Therefore noise
voltage cannot be predicted except in terms of probability statements.
Usually the characteristic of principal interest is not the instantaneous amplitude value but the
"time-averaged" value.
– 8 – IEC 60195:2016  IEC 2016
The measurement of amplitude commonly used and adopted for this International Standard is
the effective (r.m.s.) voltage E observed in a particular frequency pass-band.
n
4.1.2 Thermal noise
The thermal noise of a resistor is a fluctuating voltage caused by the random motion of
thermally agitated charges, which is present in all resistors. The root mean-square value of
the fluctuating voltage appearing at the open-circuit terminals of a resistor, which would be
indicated by the measuring system, may be calculated using Nyquist’s equation:
E = e = 4 ⋅ k ⋅T ⋅ R ⋅ ∆f
th th
where
E is the effective voltage (r.m.s. voltage) of the thermal noise in a given bandwidth;
th
e is the momentary voltage of the thermal noise in a given bandwidth;
th
–23
k is the Boltzmann constant, k ≈ 1,38 × 10 J/K;
T is the absolute temperature;
R is the resistance;
∆f is the bandwidth of the effective band-pass filter of the measuring system.
The presence of thermal noise cannot be ignored because the thermal noise of the resistor
under test is frequently a major source of interference in the measurement.
4.1.3 Current noise
The presence of direct current in a fixed resistor causes an increase in the observed total
noise above the level attributed to thermal noise. Regardless of its originating nature, this
excess noise is referred to as current noise.
2 2 2
E = E + E
t th c
where
E is the effective voltage of the total noise in a given bandwidth;
t
E is the effective voltage of the thermal noise in a given bandwidth;
th
E is the effective voltage of the current noise in a given bandwidth.
c
Hence, the current noise is the geometric difference between the total noise and the thermal
noise
2 2 2
E = E − E
c t th
The effective current-noise voltage per 1 Hz bandwidth is substantially inversely proportional
to frequency
I
[e( f )] ~
f
where
e(f) is the momentary voltage of the current noise as a function of frequency;
I is the d.c. current passing through the resistor;

f is the frequency for which the current noise voltage is considered.
The effective current noise voltage for a given bandwidth is calculated by integrating the
current noise voltage over the frequency band
f
2 2
E = [e( f )] df
c
∫
f
f
I
~ df
∫
f
f
 
f
2 2
 
~ I ln
 
f
 
where
E is the effective voltage of the current noise in a given bandwidth;
c
f is the lower cut-off frequency of the ideal band-pass;
f is the upper cut-off frequency of the ideal band-pass.
If the mean-square voltage is inversely proportional to frequency, then ideal rectangular pass-
bands having equal ratios of upper to lower band-pass limits transmit equal amounts of noise
voltage from a given noise source.
A resistor exhibiting current noise may be represented as a noise source having a zero-
impedance current-noise voltage generator connected in series with an independent thermal-
noise voltage generator and with a noise-free resistor.
4.2 Measurement principle
E is, in general, closely proportional to the applied d.c. test voltage
The current noise voltage
c
U . It is recommended, however, to apply a harmonized set of operating conditions in order to
T
ensure the most comparable measurements for all resistors.
Table 2 gives a set of operating conditions recommended for the testing of resistors with
resistances in the range of 100 Ω to 22 MΩ. The values given therein also avoid overloading
the specimen and the input circuit.
The frequency dependence of noise voltages requires the prescription of a frequency pass-
band to be used in this measurement, which is an ideal rectangular pass-band of one
frequency decade, geometrically centered at 1 000 Hz.
The measurement results in the mathematical current noise index in a frequency decade, A ′,
as follows:
 
′
E
 
′
c
A = 20lg dB
 
U
T
 
 
where
E ′ is the effective open circuit current-noise voltage in a frequency decade, given in V;
c
U is the d.c. voltage applied to the resistor under test, given in V.
T
– 10 – IEC 60195:2016  IEC 2016
The typical magnitude of the current-noise voltage being in the microvolt range rather than in
a volt range is reflected in the prevalent current noise index in a frequency decade, A ,
 E 
 c 
A = 20lg dB
 
U
T
 
where
E is the effective open circuit current-noise voltage in a frequency decade, given in µV;
c
U is the d.c. voltage applied to the resistor under test, given in V.
T
The ratio between µV and V, which results in an offset of 120 dB, is neglected in the
traditional definition of the current noise index A , hence the following relationship applies:
′
A = A − 120 dB .
1 1
Since the current-noise power spectrum approximates to a 1/f frequency characteristic, the
index and the ratio provides an estimate of current noise in any frequency decade.
4.3 Measurement system
4.3.1 Proposal of a suitable measuring system
Figure 1 shows a block schematic of a suitable measuring system.
A three-position switch may be used to access any of the three modes of operation normally
followed in the measurement procedure:
• calibration;
• measurement of system noise;
• measurement of total noise.
The input circuit consists of the resistor under test R , the isolation resistor R and the
T M
calibration resistor R , where the isolation resistor R is required to reduce the shunting
Cal M
effect of the d.c. supply system on the noise generated in the resistor under test.

R
T
R
M
S
U
T
P
U
N rms
V
V
G R
Cal
BPA
IEC
Key
P DC voltage source
G Calibration source, f = 1 kHz
S Three position switch Position 1: Calibration
Position 2: System noise
Position 3: Total noise
R Isolation resistor
M
R Calibration resistor, R = 1 Ω
Cal Cal
R Resistor under test
T
U Test voltage, d.c.
T
BPA Band-pass amplifier with adjustable gain
U Noise voltage, a.c. r.m.s.
N rms
Figure 1 – Block schematic of a suitable measuring system
The following content of this International Standard refers to this suitable measuring system,
unless otherwise specified.
4.3.2 Alternative measuring systems
The proposal of a measuring system in 4.3.1 intends to unify the test and measurement
procedures used for the assessment of the current noise generated in fixed resistors. This
system, however, is not necessarily the only system which can be used, except when
specifically designated as referee or reference methods.
The provider and user of any alternative measuring system shall demonstrate that such
system will give results equivalent to those obtained by the proposed system.
4.4 Measurement system requirements
4.4.1 Input circuit
The input impedance of the measurement system is influenced by the impedance of the d.c.
electronic voltmeter, which is in parallel with the isolation resistor R and also with the
M
resistor under test, and thereby attenuates the noise signal generated in the specimen.

– 12 – IEC 60195:2016  IEC 2016
The input impedance of the d.c. electronic voltmeter shall meet the impedance requirement
given in 4.4.4 in order to avoid any detrimental influence on the measurement.
4.4.2 Isolation resistor R
M
A number of current noise free isolation resistors R will be needed to cover the range of
M
resistance values of the specimen, which may be switched into the circuit as required. The
isolation resistor shall be current noise-free (for example, good quality wirewound resistors).
Each isolation resistor shall have a rated dissipation of at least 1 W and the resistance
tolerance shall be ±1 %.
At least four isolation resistors R are required if the range of specimen resistance extends
M
from 100 Ω to 22 MΩ. Examples for suitable values of R are 1 kΩ; 10 kΩ; 100 kΩ and 1 MΩ.
M
These values are used for establishing the test conditions in Table 2.
4.4.3 DC voltage source
The d.c. voltage source shall be capable of supplying a suitable range of voltages, which
depends on the specimen resistance R , on the required test voltage U , and on the isolation
T T
resistor R . The adjusted d.c. test voltage shall be maintained sufficiently stable throughout a
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measurement.
Table 2 provides recommended operating conditions for the specimen resistance R in the
T
range from 100 Ω to 22 MΩ, leading to test voltages U in the range from 2,2 V to 250 V. In
T
order to achieve this, the d.c. voltage source is required to provide a voltage adjustable in the
range of 14 V through 500 V.
There may be some hum and noise interference introduced by the d.c. voltage source when it
drives a current through the resistor under test. The influence of this on the observed noise
index shall not exceed 0,5 dB, when the connected test resistor is known not to generate any
current noise itself (e.g. a good quality wirewound or metal foil resistor).
4.4.4 DC electronic voltmeter
The voltmeter used for measuring the d.c. test voltage U shall have a constant impedance of
T
at least 4 MΩ in the frequency range from 0 Hz to 1 600 Hz.
The meter, in conjunction with a step attenuator, shall be capable of indicating the required
d.c. test voltages with an accuracy of ±3 %. The time constant shall be less than 0,5 s.
The meter shall support the reading of the d.c. test voltage U in volt, and the reading of the
T
d.c. test voltage index D in dB, which is determined by
 U 
T
D = 20lg  dB
 
1V
 
There may be some interference introduced by the voltmeter when it is connected to the input
circuit. The influence of this on the observed noise index shall not exceed 0,2 dB.
4.4.5 Calibration resistor R
Cal
The calibration resistor R shall meet the following specification details:
Cal
R = 1,00 Ω
Cal
P ≥ 0,5 W
r
The calibration resistor shall be selected for the lowest possible generation of current noise
(e.g. a good quality wirewound or metal foil resistor).
4.4.6 Calibration source
The calibration source shall be a stable sine-wave generator with a fixed frequency within the
range of 980 Hz to 1 020 Hz. Its output shall supply a voltage across the calibration resistor
R , which is adjustable within a range from 0,6 mV to 0,7 mV, where the actual required
Cal
calibration voltage is determined in 4.4.7. The stability of the adjusted calibration voltage shall
be better than ±2 %.
The calibration source is connected to the measuring system only in calibration mode.
4.4.7 Determination of the calibration voltage
The calibration voltage U is determined to produce a noise meter reading equal to that
Cal
produced by a current-noise voltage having an r.m.s. value of 1 mV in a frequency decade.
In 4.1.3 it has been shown that the effective current noise voltage depends of the d.c. current
and of the cut-off frequencies of the ideal band-pass like
 
f
2 2 2
 
E ~ I ln
c
 
f
 1 
where
E is the effective voltage of the current noise in a given bandwidth;
c
I is the d.c. current passing through the resistor;
f is the lower cut-off frequency of the ideal band-pass;
f is the upper cut-off frequency of the ideal band-pass.
For a frequency decade and an ideal band-pass the relationship of the two cut-off frequencies
is
f = 10 f
2 1
For the considered reference condition with
E = 1 mV
c
the above relationship is
2 2
(1 mV) ~ I ln(10)
where
I is the d.c. current passing through the resistor.
For this method an ideal band-pass filter of 1 kHz bandwidth, geometrically centered at 1 kHz
shall be used, with a lower cut-off frequency f = 618 Hz and an upper cut-off frequency
f = 1 618 Hz, see 4.4.8.
For this condition applies
– 14 – IEC 60195:2016  IEC 2016
E =U
c Cal
and hence the above relationship is
 f 
2 2
 
(U ) ~ I ln
Cal
 
f
 
where
U is the calibration voltage required to achieve a 1 mV per frequency decade reading;
Cal
I is the d.c. current passing through the resistor;
f is the lower cut-off frequency of the ideal band-pass;
f is the upper cut-off frequency of the ideal band-pass.
2 2
Dividing (U ) by (1 mV) results in
Cal
 f 
 
ln
2  
f
(U )
 1 
Cal
=
ln(10)
(1mV)
and finally in the determination of the calibration voltage as
 
f
 
ln
 
f
 1 
U = ×1mV
Cal
ln(10)
For practical use this equation may be simplified to
U = A ⋅ 0,659 mV
Cal
where
A is a non-dimensional value representing the area under the pass-band curve
f
A = ln
f
where
f is the lower cut-off frequency of the ideal band-pass;
f is the upper cut-off frequency of the ideal band-pass.
For the prescribed ideal band-pass filter of 1 kHz bandwidth, geometrically centered at 1 kHz,
the calculation results in A = 0,962.
i
Hence, for this case the required calibration voltage is
U = 0,962 × 0,659 mV = 0,646 mV
Cal
For any particular non-ideal band-pass filter, value A can be computed as follows.

a) The voltage gain is measured throughout the pass-band of the system versus frequency,
where the voltage gain is the ratio of the output voltage, as indicated by the output meter,
to the input voltage, applied across the terminals of the calibration resistor.
b) The power gain is calculated by squaring of the voltage gain for each frequency.
c) Each power gain value is divided by its respective frequency and plotted against
frequency in a linear diagram.
d) The area under the resulting curve is planimetrically measured to give the value A for the
respective non-ideal band-pass filter, where the accuracy of this determination shall be
within ±2,5 % of the result.
Where there is the result of a numerical simulation available of the gain over frequency of a
designed band-pass filter, with the gain typically given in dB, the procedure described above
can be executed numerically, e.g. using a calculation spreadsheet.
The resulting value A should be close to the result for an ideal band-pass, A = 0,962.
i
NOTE The numerical determination of the area under the pass-band shown in Figure 2 results in a value
A = 0,959, which leads to a required calibration voltage U = 0,645 mV.
Cal
The calibration source shall be adjusted to provide the r.m.s. voltage U at the terminals of
Cal
the calibration resistor R with a relative accuracy of better than ±2 %.
Cal
4.4.8 AC band-pass amplifier
The amplifier gain shall be sufficient to measure circuit noise with the input terminals shorted
and with the adjustable gain control, described below, set near its minimum gain position.
In a verification with R ≥ 100 kΩ and no d.c. current present, the circuit noise shall be no
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greater than that equivalent to the thermal noise of a 6,2 kΩ resistor. Therefore, the increase
in the output reading when the short is replaced by a resistor of 6,2 kΩ with a relative
tolerance of ±5 % shall be at least 3 dB with the gain control setting kept unchanged.
The amplifier shall be capable of measuring input signals up to 650 µV. This signal amplitude
gives a scale reading of approximately 60 dB when the system is calibrated.
A continuously adjustable gain control shall be provided for maintaining a fixed overall system
gain which would otherwise vary with input conditions listed in Table 2. The necessary gain
control range is approximately 33 dB.
The pass-band shall be flat, shall have a fixed half-power pass-band of approximately
1 000 Hz within the limits ±50 Hz and shall be geometrically centered at 1 000 Hz ± 50 Hz.
Ripple in the flat top of the pass-band shall not exceed ±0,2 dB. Figure 2 shows the transfer
function of a band-pass meeting these requirements.

– 16 – IEC 60195:2016  IEC 2016
–3
–20
–40
–60
100 290 618 1 000 1 618 3 400 10 000
Frequency (Hz)
IEC
Figure 2 – Typical transfer function of the band-pass amplifier
These requirements shall be satisfied for all measurement conditions listed in Table 2. Neither
the area under the pass-band, A, as determined in 4.4.7, nor the half-power pass-band shall
vary with respect to measurement condition by more than ±4 % for any recommended
measurement condition. Compliance at 100 Ω and at 22 MΩ is considered sufficient.
The a.c. amplifier shall respond to noise signals without introducing a significant error due to
clipping. This requires the dynamic range to extend at least 10 dB beyond the indicated a.c.
r.m.s. value.
4.4.9 AC r.m.s. meter
The a.c. measuring system shall be calibrated in dB from −20 dB to at least +60 dB with 0 dB
being 1 µV in a frequency decade. The accuracy of the a.c. r.m.s. meter shall be ±0,4 dB. The
time constant shall be in the range of 0,8 s to 1,5 s.
4.4.10 Test fixture
The test fixture for the resistor under test, R , shall be capable of providing a safe electrical
T
connection and sufficient shielding from any external fields.
The lead-to-lead and lead-to-ground capacitances of the resistor under test in its test fixture
and of the leads to the input of the band-pass amplifier shall be minimized, e.g. by the use of
short leads, adequate spacing and careful mounting.
Good shielding practice shall be adopted in the construction of the measurement system. The
input circuit operates at extremely low signal levels, which makes it necessary that all parts
and leads in the input circuit be very well shielded. Components carrying large signals should
not be located near the input circuit.
Gain (dB)
4.5 Verification of the measuring system
4.5.1 Performance check by measurement of instrument and thermal noise
It is recommended to verify the performance of the measurement system by checking the
level of system noise, including thermal noise, without involving any specimen.
For a measurement system as proposed in 4.3, the following procedure should be applied:
a) turn the function switch to “calibration” and short-circuit the terminals for the specimen R ;
T
b) adjust the gain of the band-pass amplifier to the calibrate line on the a.c. r.m.s. meter;
NOTE The calibration line typically is a line centred on the a.c. r.m.s. meter scale. With the measuring system
set in calibration mode the meter is connected without an attenuator network.
c) turn the function switch to “system noise” and read the noise index S ;
k
d) remove the short circuit from the terminals for the specimen R ;
T
e) read the noise index S for each isolation resistor R .
o M
The readings of the noise index should fall within the limits given in Table 1, unless other
recommendations are given for a specific measuring system.
Table 1 – Permissible limits of system noise
R R Permissible limits of system
M T
noise reading
dB
Any Short circuit
S ≤ −5 dB
k
None, terminals open
1 kΩ −9 dB ≤ S ≤ −4,5 dB
o
10 kΩ None, terminals open
−5 dB ≤ S ≤ −2 dB
o
100 kΩ None, terminals open 5 dB ≤ S ≤ 7,5 dB
o
None, terminals open
1 MΩ 14 dB ≤ S ≤ 18 dB
o
The first two readings are essentially measurements of the noise in the amplifier, while the last two readings are
essentially measurements of thermal noise of R in the pass-band of the instrument. The third reading is
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influenced by both factors.
There may be different performance check procedures and permissible limits prescribed for
practical realizations of the measurement system proposed in 4.3.1, or for alternative
measuring systems as suggested in 4.3.2.
4.5.2 Performance check by comparison of repeated measurements
It is recommended to verify the performance of the measurement system by checking the
current noise of specific resistor specimens after repeated measurements.
A practical means of monitoring the stability of the measurement system is to keep a record of
the measurements made on a set of specific control resistors, where it is desirable for the set
of control resistors to consist of different types of resistors and to represent a large range of
resistance and current-noise values.
Plotting the data against time in the form of a control chart for each specimen is suggested as
a simple and effective means for detecting any irregularity within the measurement system.

– 18 – IEC 60195:2016  IEC 2016
5 Measurement procedure
5.1 Ambient conditions
The measurement shall preferably be made under standard atmophere for referee
measurements and test as given in IEC 60068-1:2013, 4.2.
– Temperature: 23 °C ± 2 °C
– Relative humidity: 45 % to 55 %
– Air pressure: 86 kPa to 106 kPa
A relevant specification may prescribe other ambient conditions for this measurement.
NOTE The generally applied standard atmospheric conditions for testing with their wider permissible temperature
range are not recommendable for this test due to the influence of temperature on the measurement, e.g. by means
of thermal noise.
5.2 Preparation of specimen
The specimen shall be stored at the ambient conditions prescribed in 5.1 for at least 24 h
before a measurement is made.
5.3 Procedure
5.3.1 General
The measurement system shall be stored at the ambient conditions prescribed in 5.1 for at
least 24 h before a measur
...