The New CISPRs: 11 and 22

Two European Norm standards—EN 55011 and EN 55022—are the most widely referenced emissions documents in use in the electromagnetic compatibility world. They are based on CISPR 11 (for industrial, scientific, and medical apparatus) and CISPR 22 (for information technology [IT] equipment), standards from the Comite International Special des Perturbations Radioelectriques (CISPR). Since they are referenced in many other product standards, though, their influence stretches beyond the confines of this field.

The first edition of CISPR 11 was published in 1975 and the second in 1990; the CISPR 22 editions were published in 1985 and 1993. The third editions of both were published at the end of 1997 by the International Electrotechnical Commission (IEC) and adopted in 1998 by the European Committee for Electrotechnical Standardization (CENELEC). Both of the new editions were harmonized in the Official Journal of the European Communities on February 27, 1999.

The dates of cessation of presumption of conformity (that is, the dates after which declarations to the previous editions may not be made) are January 1, 2001, for EN 55011 and August 1, 2001, for EN 55022. Manufacturers and test houses therefore need to be aware of the changes in each document that may affect their test and certification strategies.

The changes in CISPR 11 are relatively minor and will directly affect only a few types of product. Induction cooking appliances and x-ray diagnostic machines are particular targets.

One change allows a more flexible measuring distance for radiated measurements in situ. Another allows use of the voltage probe for high-current equipment under test (EUT) with a specific set of limits.

There is a new clause on assessment of conformity of equipment, which is a rewritten and substantially modified version of the old clause 6. It invokes the 80%/80% rule for equipment in series production, assessed according to the usual method.

The new clause also explicitly states that measurements obtained from equipment in its place of use and not on a test site relate to that installation only. They shall not be considered representative of any other installation.

A new paragraph introduces the concept of "equipment in small-scale production," that is, equipment manufactured on a continuous or a batch-production basis. This rule allows the evaluation for compliance for such equipment to be made on a single sample, chosen randomly.

The changes in CISPR 22 are much more extensive. Amendments to the second edition made substantial modifications to the general measurement conditions, and these have been retained in the third edition. Additional changes include paragraphs on a range of issues including

The sections on measurement methods for both conducted and radiated disturbances have a new addition that allows the use of a peak detector "to reduce testing time." Measurements with the proper quasi peak and/or average detector(s), however, take precedence in cases of dispute. Some further changes that appeared in the second edition relating to the measurement setup, and figures illustrating these, are retained.

The most important change in the third edition of CISPR 22 is the inclusion of test requirements for telecommunication ports. This change will be a source of concern for both test houses and manufacturers of many IT products, especially those who have not had to consider this aspect previously.

Telecommunication ports are defined as those "which are intended to be connected to telecommunications networks (e.g., public-switched telecommunications networks, integrated services digital networks), local-area networks (e.g., Ethernet, Token Ring), and similar networks." However, there is a possibility that other product standards will reference these tests for signal lines in general.

Clause 5 of the third edition now includes new limits for conducted common-mode disturbances at these ports. They are presented as both current and voltage limits (the choice depends on measurement method) for classes A and B. The current and voltage limits are related by common-mode impedance of 150 W.

The changes incorporate a wholly new method of measurement of disturbances at telecommunication ports. A new normative annex gives test setups for common-mode measurements. The requirements for the impedance stabilizing network (ISN) to be used for conformance testing voltage or current measurements are given as a common-mode terminating impedance of 150 W, a minimum isolation from the associated equipment, and a specified longitudinal conversion loss.

Further measurement methods are defined for different types of cable connections. These methods and setups are for use "where the specified ISNs are not applicable." Provision is made for using the following:

The diagrams showing the test setup presented in the 1993 revision are reproduced in the third edition, with one important difference: wherever there was a direct connection shown from the EUT to associated equipment, that connection is now shown passing through an ISN. This change appears to be meant to apply to any "I/O signal cable intended for external connection"—not just to telecommunication ports.

Because of the variety of methods and equivocal nature of the specification, test houses are likely to experience difficulty in interpreting and carrying out the test. They will also have to invest in a number of new ISNs to be able to cover the test in depth. Manufacturers would be advised to look carefully at these new requirements to determine how likely they are to affect their product testing and certification in the near future.

Tim Williams is employed with Elmac Services (Chichester, UK). He may be contacted by telephone at +44 1243 533361, by fax at + 44 1243 780168, or by e-mail at elmactimw@cix.co.uk.