Pattern approval

Pattern approval, also called type approval, is a certificate issued by a national metrology institute stating that a sample of an instrument design has been tested against the full pattern-evaluation procedure of IEC 61672-2 and found to meet the requirements of IEC 61672-1 for its class. It is the strongest independent evidence that a design conforms to the standard, and in a number of countries it is a legal precondition for using the instrument in measurements that have official effect. It is also widely misunderstood, so this page sets out what it is and what it is not.

Who issues it

Approvals are issued by national metrology institutes or bodies designated by them. Those most often seen on sound level meter datasheets are listed below; others, including bodies in the Czech Republic, Poland, Portugal, Spain, China and Japan, appear on individual instrument pages where the manufacturer cites them.

What pattern approval is

• A test of the design. One or more samples of a specific configuration, meaning the meter, microphone, preamplifier, windscreen and firmware named in the certificate, are tested against every clause of IEC 61672-1 by the procedures of IEC 61672-2. Where filters are included, IEC 61260-2 applies.
• Independent. The tests are done by the institute or an accredited laboratory acting for it, not by the manufacturer. The certificate, with its number and revision, is a public document.
• Configuration-specific. The approval names the components covered. A different microphone, an outdoor kit or a major firmware change requires an extension of the approval, which is why certificates carry revision numbers.
• The gateway to legal verification. In countries with legal metrology for sound level meters, only approved designs can be submitted for the periodic verification of individual instruments that the law requires.

What pattern approval is not

• Not a calibration of your instrument. Approval says the design meets the standard. Whether a particular serial number does so today is shown only by a periodic test to IEC 61672-3 or an official verification, which must be repeated at intervals.
• Not a mark of higher performance. An approved class 1 meter and an unapproved one may be identical in performance; the difference is that one has been independently shown to meet the limits. Many manufacturers do not seek approval for instruments sold mainly in markets that do not require it.
• Not universal. The United Kingdom, the United States and most of Asia, Africa and the Americas have no legal metrology requirement for sound level meters; a current laboratory calibration certificate is what regulators there expect. An approval from one country is not automatically recognised in another, although the test results often are.
• Not a statement about fitness for a measurement. It does not cover the noise floor, logging, software or the user’s procedure. A measurement to ISO 1996-2 with an approved meter at the wrong position is still wrong.

When it is needed

Buy a pattern-approved instrument when measurements will be used for enforcement, licensing or litigation in a country that requires it, when a client’s procedure calls for it, or when the instrument will be used across several European countries and the question is likely to arise. In Germany, France, Switzerland and Austria the requirement is routine for consultants and authorities. Elsewhere, approval is useful as evidence of conformance but a calibration certificate from a laboratory accredited to ISO/IEC 17025 does the practical work; see Sound level meter calibration and verification. Approved instruments are almost always IEC 61672-1 class 1; approval of class 2 designs is rare.

Reading an approval statement

A complete statement names the body, the certificate number and revision, and the configuration covered. “PTB” alone on a datasheet tells you that an approval exists but not for which microphone or firmware; the certificate itself, which manufacturers usually publish, does. Approvals that are optional, meaning the instrument can be ordered with or without the approval-specific configuration, are flagged as such where the manufacturer says so.

Instruments listing an approval

The table lists every instrument in the database for which the manufacturer publishes one or more pattern approvals, quoting the statement as given. The absence of an instrument from this table means the manufacturer does not publish an approval, not that none exists.