Editor’s Note—This article was originally published in 2010 in In Compliance Magazine, and has been updated to include recent progress on the development of Edition 6.0 of CISPR 11.
CISPR is the International Special Committee on Radio Interference which was founded in 1934. The International Standard for electromagnetic emissions (disturbances) from industrial, scientific and medical (ISM) equipment is CISPR 11. The official title of the standard is “Industrial, Scientific, and Medical Equipment – Radio-Frequency Disturbance Characteristics – Limits and Methods of Measurement.” The premiere edition of the standard was released in 1975 and the current edition (fifth edition) was released in 2009. The standard includes both limits and methods of measurement for conducted-emissions and radiated-phenomena. This article traces the history and development of the content of the standard over the last 40 years.
First Edition—1975
The title of the Premiere Edition was “Limits and Methods of Measurement of Radio Interference Characteristics of Industrial, Scientific, and Medical (ISM) Radio-Frequency CISPR Subcommittee B (Interference from Industrial, Scientific, and Medical Apparatus).” It summarized the technical content of a number of CISPR publications, recommendations and reports over a period of eight years, from 1967 to 1975.
The frequency range covered by the first edition of the standard was 150 kHz to 18 GHz. The terminal voltage limits were quoted in millivolts and covered the frequency range 150 kHz to 30 MHz. Terminal voltage limits from the first edition are reproduced in Table 1.
The radiated limits were quoted in microvolts per meter for the frequency range 0.150 MHz to 1000 MHz. They were quoted at antenna-measurement distances of 30, 100, and 300 meters from the equipment or 30 meters or 100 meters from the boundary of the users’ premises. Limits of radiation in microvolts/meter and decibels (uV/m)] from the first edition is recreated in Table 2.
There was a special limit for radiation from microwave equipment used for heating and medical purposes in the frequency range from 1-18 GHz; it was 57 dB above a picowatt effective radiated power (ERP), referred to a half-wave dipole.
Methods of measurement quoted CISPR Publications 1, 2, and 4 for quasi-peak measuring sets. Measurement of the radio-frequency voltage on supply mains (AC voltage lines) was conducted with a V-network with an intrinsic impedance of 150 ohms.
Magnetic field measurements are made with a balanced loop antenna below 30 MHz. For signals greater than 30 MHz, an “electric aerial” would be used as per CISPR Publications 2 and 4. The center of the “aerial” would be 3 meters above the ground.
Above 1 GHz, the “receiving aerial” was to be made with a directive aerial of small aperture capable of making separate measurements of the vertical and horizontal components of the radiated field. The height of the aerial had to be the same as the height of the approximate radiation center of the equipment under test.
Second Edition—1990
The second edition of CISPR 11 was released in 1990, and it contained numerous changes from the original 1975 edition, as well as two amendments.
In this edition, ISM Equipment was divided into two groups and two classes. Group 1 equipment included all ISM equipment that used RF energy only for internal functioning of the equipment, while Group 2 equipment included ISM equipment used for external treatment of material and similar processes. Class A equipment is equipment suitable for use in all establishments other than domestic buildings, while Class B equipment is equipment suitable for use in domestic surroundings.
The frequency bands for conducted emissions were stated as covering 150 kHz to 30 MHz. The second edition included new separate limits for Class A and Class B equipment. The Class A equipment limits in dBuV are shown in Table 3.
The Class B equipment Limits in dBuV are shown in Table 4.
Electromagnetic radiation disturbance limits in dBuV/m for Group 1 equipment in Edition 2 are shown in Table 5.
There were additional limits for radiated emissions for Group 2 equipment.
In the frequency range 1 GHz to 18 GHz, the limit for radiation disturbance power was 57 dB above a picowatt (effective radiated power), referred to a half-wave dipole in the narrow frequency range 11.7 GHz to 12.7 GHz.
The standard used statistics for compliance conclusions. Clause 6.1 stated “it cannot be shown that equipment in series production fails to meet the requirements of this publication without a statistical assessment of compliance being carried out.”
In the General Measurements Requirements clause, the standard provided for the measurement of Class A equipment either on a test site or in situ as determined by the manufacturer. However, the standard mandated that Class B equipment be tested and measured in a testing laboratory only.
Measuring equipment used by a testing lab had to comply with CISPR 16. Receivers needed both average and quasi-peak capability. An artificial mains network (LISN) was needed for conducted emissions, and it was a 50 ohm-50 microhenry network. Antennas used included a loop antenna below 30 MHz and a balanced-dipole antenna from 30 MHz to 1000 MHz. Measurements were made in both horizontal and vertical polarizations. Class A equipment was measured with the center of the antenna three meters above ground while, for Class B equipment, the center of the antenna had to be adjusted to between one and four meters.
The testing laboratory had to meet special provisions for measuring radiated emissions, including a minimum-sized ground plane, and an area free of reflecting structures and also large enough to allow for the appropriate separation of the equipment under test and the receiving antenna.
Amendment 1 to the second edition was released in March of 1996. It changed some conducted emission limits, especially for Class A equipment. Amendment 2 was also released in March of 1996 and it contained limits for induction cooking appliances for both conducted limits and radiated magnetic field limits. Amendment 2 also modified radiation limits for Group 2 equipment.
Third Edition—1997
The third edition of CISPR 11 was also developed by CISPR Subcommittee B and was released in 1997. It replaced the second edition and its two amendments.
The main content of CISPR 11 standards are based on the original CISPR Recommendation No. 39/2, entitled “Limits and Methods of Measurement of Electromagnetic Disturbance Characteristics of Industrial, Scientific, and Medical (ISM) Radio-Frequency (RF) Equipment.” The Recommendation states “The CISPR, considering a) that ISM RF equipment is an important source of disturbance; b) that methods of measuring such disturbances have been prescribed by the CISPR; c) that certain frequencies are designated by the International Telecommunication Union (ITU) for unrestricted radiation from ISM equipment, recommends that the latest edition of CISPR 11 be used for the application of limits and methods of measurement of ISM equipment.”
The third edition of the standard reorganized the first Clause, changing it from “Scope and Object” to “General,” and comprised of two Sub-clauses, “Scope and Object,” and “Normative References.”
Clause 6 of the second edition was renumbered as Clause 11 in the third edition, and Sub-clause 6.1, “Equipment in series production,” was replaced with Sub-clause 11.2, “Equipment in small scale production.”
A new Sub-clause 5.4, “Provisions for Protection of Specific Sensitive Radio Services,” was added in Clause 5, “Limits of Electromagnetic Disturbance.”
Clause 7 in the second edition became Clause 6 in the third edition; Clause 8 became Clause 7, Clause 9 became Clause 8, Clause 10 became Clause 9, and Clause 11 became Clause 10.
Annexes A – D remained the same in the third edition as in the second. Two new annexes were added, Annex E, “Safety-Related Service Bands,” and Annex F, “Sensitive Service Bands.”
The classification of equipment remained the same from the second to the third edition, that is, Group 1 and Group 2, and Class A and Class B.
With respect to the limits of electromagnetic disturbance, Class A equipment could still be tested either at a testing laboratory or in situ, while Class B equipment had to be measured in a testing laboratory.
The limits for conducted emissions on the power leads were measured from 150 kHz to 30 MHz using a 50-ohm/50-uH network. The limits remained the same for Class A and Class B equipment from the second edition of the standard, except that another category was added for Class A-Group 2 equipment for mains supply currents in excess of 100 amps per phase when using the CISPR voltage probe. The limits for this special case are shown in Table 6.
However, new limits were added in Table 2c in the standard (“Mains terminal disturbance voltage for inductive cooking appliances”) for Group 2-Class B equipment for both domestic and commercial cooking appliances.
Table 3 in the standard (“Electromagnetic radiation disturbance limits for group 1 equipment”) had a major change, as the measurement distance for Group 1-Class A equipment was changed from 30 meters to 10 meters with a corresponding increase in limits of 10 dB (assuming an inverse distance fall-off of the radiated electromagnetic field).
Clause 5.2.2 of the third edition also introduced the concept of measuring products at shorter distances than the specified measurement distances for radiated disturbances. For example, it allowed Group 2-Class A equipment to be measured at a distance of between 10 and 30 meters instead of 30 meters. Also, it allowed Group 1 and 2-Class B, equipment to be measured at antenna distances between three and 10 meters. However, it stated that “in case of dispute, Class A-Group 2 equipment shall be measured at a distance of 30 meters; Class B-Group 1, Class B-Group 2, and Class A-Group 1 equipment shall be measured at a distance of 10 meters.”
Tables 3a and 3b were added in the third edition to cover Group 2 induction cooking appliances for Class B and Class A, respectively. Table 3a (“Limits of the magnetic field induced current in a 2-m loop antenna around the device under test”) was intended to use the Van Veen Loop Method measurement method as per CISPR 16-2. Table 3b (“Limits of the magnetic field strength”) is measured at a three meter antenna distance with a 0.6 meter loop antenna as described in CISPR 16-1.
Table 4 in the standard (“Electromagnetic radiation disturbance limits for Group 2-Class B equipment measured on a test site”) added a new column of requirements, that the quasi-peak magnetic field (measured at three meters) will not exceed 39 dBuAmp/meter decreasing linearly with the logarithm of the frequency to 3 dBuAmp/meter from 150 kHz to 30 MHz.
Table 5 in the standard changed the measurement distance from 30 meters to 10 meters and increased the limits by 10 dB from the limits found in the second edition.
Table 6 was added to the third edition of CISPR 11. It was entitled “Electromagnetic radiation disturbance peak limits for Group 2-Class B ISM equipment producing CW-type disturbances and operating at frequencies above 400 MHz.” Table 7 (“Electromagnetic radiation disturbance peak limits for Group 2-Class B ISM equipment producing fluctuating disturbances other than CW and operating at frequencies above 400 MHz”) and Table 8 (“Electromagnetic radiation disturbance weighted limits for Group 2-Class B ISM equipment operating at frequencies above 400 MHz”) were also added.
Clause 5.4 (“Provisions for protection of specific sensitive radio services”) was added to the third edition. It referenced a new Annex F which gave examples of bands to be protected.
The same general measurement conditions existed as in the previous edition which is that Class A equipment could be measured at a test lab or in situ. Class B equipment had to be measured on a test site (in a test lab).
For equipment on a turntable, the distance to the antenna was measured from the center of the turntable. For equipment not on a turntable, the distance to the antenna was measured from the edge of the equipment.
Paragraph 6.5.6 (“Single and multiple-zone induction cooking appliances”) was added to the third edition.
Amendment 1 to the third Edition added requirements for ISM lighting apparatus operating in the frequency bands of 915 MHz, 2.45 GHz, and 5.8 GHz. It also added IEC 60705:1999 (“Household microwave ovens – methods for measuring performance”) to the normative standards. It also added new words in Clause 5.2.2 (discussed earlier) and it added a new Table 5 (“Electromagnetic Radiation disturbance limits for Group 2 – Class A equipment”). All new wording was added to Clause 5.2.3 by Amendment 1. In Clause 6.2.1, it added the requirement that “for measurements at frequencies above 1 GHz, a spectrum analyzer with characteristics as defined in CISPR 16-1 shall be used.” Additionally, in Clause 6.2.4, it added the words “for measurements at frequencies above 1 GHz, the antenna used shall be as specified in CISPR 16-1.” Also, Clause 6.5.4 (“Microwave cooking appliances”) was added by Amendment 1.
An important (and somewhat controversial) Sub-clause was added by Amendment 1 in Clause 7.1.3 (“Radiation measurements [9 kHz to 1 GHz]”). It added two sentences that impacted the third edition and subsequent editions. The first sentence said “for the test site measurements, an inverse proportionality factor of 20 dB per decade shall be used to normalize the measured data to the specified distance for determining compliance.” Also, it added the parenthetical sentence, “care should be taken in measuring a large test unit at 3 meters at a frequency near 30 MHz due to near-field effects.” It deleted a key sentence from the second edition that said “at the closer measurement distance the electromagnetic disturbances measured shall not exceed the limit values specified in Clause 5.” In Sub-clause 8.2 it added the sentence “the distance between the receiving antenna and the EUT shall be 3 meters.” Sub-clauses 8.3 (“Validation and calibration of test site”) and 8.4 (“Measuring Procedure”) were completely rewritten. Finally, Amendment 1 added Figure 5 (“Decision tree for the measurement of emissions from 1 GHz to 18 GHz of Class B-Group 2 ISM equipment operating at frequencies above 400 MHz”).
Amendment 2 replaced “spark erosion equipment” with “electro-discharge machining (EDM) and arc welding equipment.” It also made additional editing changes to a number of Sub-clauses.
Fourth Edition—2003
The fourth Edition of CISPR 11 was published in March 2003. The fourth edition superseded the third edition (1997), along with its first amendment (1999) and its second amendment (2002).
There were a limited number of changes in the fourth edition from the third edition. The first two sentences in Clause 4 were changed to read “the manufacturer and/or supplier of ISM equipment shall ensure that the user is informed about the class and group of the equipment, either by labeling or by the accompanying documentation. In both cases, the manufacturer/supplier shall explain the meaning of both the class and the group in the documentation accompanying the equipment.”
Clauses 7.1 and 7.2 were interchanged from the third edition.
Clause 6.2.5 (“Artificial Hand”) was added to the fourth edition, as well as Figure 6 (“Artificial Hand, RC Element”). The concept of an artificial hand was introduced to simulate the effects of the user’s hand during the conducted emission measurements
The definitions of Group 1 ISM equipment, Group 2 ISM equipment, Class A equipment, and Class B equipment remained basically the same as the third edition.
With respect to limits of electromagnetic disturbance, Class A equipment could once again be measured either in a testing laboratory or in situ (as preferred by the manufacturer). However, the fourth edition continue to require Class B equipment to be measured in a testing laboratory.
The limits of terminal disturbance voltage (conducted emissions) gives the manufacturer two choices: 1) meet the average limit with an average detector and the quasi-peak limit with a QP detector; or 2) meet the average limit when using a QP detector. This was the same as stated in the third edition.
For radiated disturbances from 150 kHz to 1000 MHz, the limits stayed basically the same as those found in the third edition. Measurements were allowed at closer distances than the specified distances under certain considerations. In case of dispute, however, Class B (Group 1 and Group 2) and Class A (Group 1) were to be measured at a distance of 10 meters, while Class A (Group 2) were to be measured at a distance of 30 meters.
Receivers used for the measurements were expected to meet the criteria of CISPR 16-1. Requirements for the artificial mains network (LISN) remained the same as those in the third edition, that is, a 50 ohm/50 microhenry V-Network as specified in CISPR 16-1. The antennas used for measuring CISPR 11 products were also expected to meet CISPR 16-1 requirements. In a testing laboratory, the antenna must be raised and lowered from one to four meters in the frequency range 30 MHz to 1000 MHz. For measuring products in situ, the antenna’s center must be fixed at two meters above the ground.
Amendment 1 to the fourth edition was released in 2004. Primarily, Amendment 1 replaced Table 6 in the fourth edition with a new table that addresses Group 2 (Class A and Class B) ISM equipment producing CW type disturbances and operating at frequencies above 400 MHz.
Amendment 2 added CISPR 16-4-2:2003 to the Normative References. It also added a new Table 2c for Mains Terminal disturbance voltage for induction cooking appliances. It also modified Clauses 6.5.4 (“Microwave Cooking Appliances”) and 6.5.6 (“Single and multiple-zone induction cooking appliances”) to more closely match the IEC Product Standard. Amendment 2 also added Clauses 6.6 (“Recording of test-site measurement results”), 6.6.1 (“Conducted Emissions”), and 6.6.2 (“Radiated Emissions”). Also, Clause 11.4 (“Measurement Uncertainty”) was added, stating that “determining compliance with the limits in this standard shall be based on the results of the compliance measurement, not taking into account measurement instrumentation uncertainty.” However, results of measurements of emissions from ISM equipment were supposed
to reference the measurement uncertainty considerations contained in CISPR 16-4-2.
Fifth Edition—2009
Released in 2009, the fifth edition of CISPR 11 is the current edition of the standard. It continues the long-standing practice of Group 1 and Group 2, Class A and Class B equipment classifications. The limits stated in the fifth edition are similar to the limits found in the fourth edition.
Table 7 presents a side-by-side comparison of the table of contents for the first edition and the fifth edition of CISPR 11, which clearly shows the growth in the length and complexity of the standard over a period of 35 years.
Clause 6 in the fifth edition represents a major overhaul from that in the fourth edition. Its Main Clause and Sub-clause headings are as follows:
Clause 6 – Limits of Electromagnetic Disturbance
6.1 – General
6.2 – Group 1 Measured on a Test Site
6.3 – Group 2 Measured on a Test Site
6.4 – Group 1 and Group 2 Class A Measured in situ
Clause 7 added a new Sub-clause 7.1 (“General”) and a new Sub-clause 7.7 (“Recording of Test Site Measurement Results”).
Clause 12 (“Assessment of Conformity of Equipment”) added a new Sub-clause 12.1 (“General”) and then the next three Sub-clauses were the same as Sub-clauses 11.1–11.3 in the fourth edition.
Clause 13, titled “Figures and Flowcharts,” is new to this edition, as is Annex E.
The entire fifth edition was written to provide a more transparent structure. Table 17 in the standard was added with a title of “Electromagnetic Radiation Disturbance Limits for Class A (Group 1) Equipment Measured in situ.” It specifically addresses equipment with input power greater than 20 KVA.
An Amendment 1 to the fifth edition was released in 2010. It created a new subset of equipment, “Small Equipment.” Small Equipment is defined as “equipment, either positioned on a table top or standing on the floor which, including its cables, fits in a cylindrical test volume of 1.2 meters in diameter and 1.5 meters above the ground plane.”
Using this definition, Tables 4, 5, 9, 10, and 11 in the standard were modified to allow testing of Class A and B products meeting the “Small Equipment” definition to be tested at a three meter test distance. The limit at three meters would be extrapolated from the typical test distance of 10 meters using an inverse-distance fall-off assumption (free-field).
Toward the Sixth Edition—2015
Since the release of Amendment 1 to the fifth edition of CISPR 11 in 2010, Subcommittee B of CISPR has been working on the sixth edition of the standard. At its most recent meeting in Frankfurt Germany in October 2014, Subcommittee B made significant progress on the merging of several new elements into CISPR 11 toward the release of a Final Draft International Standard (FDIS). This FDIS is scheduled for National Voting beginning in April 2015.
New elements or supplements found in the FDIS for CISPR 11 are expected to include:
- Emission requirements for grid-connected power converters (GCPCs)
- Use of the amplitude probability distribution (APD) method and associated limits for the assessment of fluctuating RF disturbances in the range above 1 GHz
- Alignment of emission requirements for disturbance sources generating fluctuating disturbances with those from sources generating continuous wave (CW)-type disturbances
- Emission requirements for GCPCs with greater than 20 KVA rated throughput power.
The FDIS will also include general maintenance items to address other issues in the fifth edition of the standard.
Summary and Conclusions
The CISPR 11 standard for measuring disturbances (emissions) from ISM equipment has been in existence for 40 years. It has grown from a simple document to a complex document involving a number of types of products. It has grown from measuring products at a larger distance (100 meters and 30 meters) for Class A equipment to measuring them at three meters. Class B equipment measurement distances have shrunk to three meters, the distance used in the U.S. since the release in 1979 of FCC’s rules on computer emissions. This steady erosion of the “laws of physics” for Class A products is worrisome and a trend to reverse this erosion is overdue in the engineering field of EMC and the EMC standards arena.
Daniel D. Hoolihan is the founder and principal of Hoolihan EMC Consulting. He serves as chair of the ANSI-ASC C63 Committee on EMC. He is also a past-president of the IEEE’s EMC Society, and a current member of the Society’s Board of Directors. Hoolihan is also an assessor for the NIST NVLAP EMC and Telecom Laboratory Accreditation program. He can be reached at danhoolihanemc@ aol.com, or at 651-213-0966.
