IEC 61252

IEC 61252 specifies personal sound exposure meters, the instruments usually called noise dosimeters. It is the standard to look for on a dosimeter datasheet in the same way that IEC 61672-1 is for a sound level meter. The American counterpart is ANSI/ASA S1.25, which covers the same instrument but adds the exchange-rate, criterion and threshold settings used in United States regulation; most dosimeters sold internationally state conformance to both.

Editions

The first edition was published in 1993 and has been amended twice, in 2000 and 2017, giving the consolidated edition 1.2 that most current datasheets cite. A revised edition has been in preparation and is beginning to appear on the datasheets of newly announced instruments; where a manufacturer cites it, the statement is reproduced as given. The 2017 amendment aligned terminology with IEC 61672-1 and modernised test conditions without changing the essential tolerances.

What a personal sound exposure meter measures

The fundamental quantity is A-weighted sound exposure, the time integral of the squared A-weighted sound pressure over the measurement period, expressed in pascal-squared hours. Everything a dosimeter reports is derived from it: the daily noise exposure level L_EX,8h used in ISO 9612 and European regulation, the time-weighted average and percentage dose used in American regulation, and the L_Aeq of the measurement period. An exposure of 1 Pa²h corresponds to an L_EX,8h of about 85 dB(A). The standard requires the instrument to display sound exposure or a quantity derived from it, and to indicate overload.

Occupational regulations also limit the C-weighted peak sound pressure level, and nearly every dosimeter measures it. Peak measurement and the 5 dB exchange rate are features that regulations and ANSI S1.25 require rather than the core of IEC 61252, which is built on the equal-energy (3 dB) principle inherent in integrating sound exposure. The guide How to choose a noise dosimeter explains the settings.

Tolerances and tests

IEC 61252 sets tolerances on the A-weighting frequency response, on level linearity over the operating range, on the accuracy of time integration for steady and tone-burst signals, and on the effects of temperature, humidity, static pressure, vibration and electromagnetic fields. The tolerances correspond broadly to class 2 of IEC 61672-1, reflecting the fact that a shoulder-mounted microphone close to the body cannot deliver class 1 accuracy whatever the electronics do. The standard specifies the reference orientation and the acoustic test conditions for a microphone that is intended to be worn rather than pointed at a source, and it requires the manufacturer to publish the effect of the body and clothing where known.

Relationship to IEC 61672-1 and ISO 9612

A dosimeter is not a sound level meter under IEC 61672-1 unless the manufacturer also claims that standard, and several do, usually at class 2, so that the same instrument can be used for spot measurements. ISO 9612, the measurement standard for occupational exposure, accepts either a dosimeter to IEC 61252 or a sound level meter to IEC 61672-1 class 1 or 2 and sets out three strategies, task-based, job-based and full-day, for using them. It also requires an acoustic calibrator check before and after each measurement and an uncertainty estimate that includes instrument, sampling and microphone-position contributions.

Calibration

IEC 61252 has no separate periodic-test part like IEC 61672-3. Laboratories calibrate dosimeters to the manufacturer’s procedure or to the requirements of IEC 61252 itself, reporting the calibration level, the frequency response and the linearity with uncertainties. Field checks use an acoustic calibrator to IEC 60942 with an adaptor for the small microphone; badge-type instruments often dock in a reader that contains a calibrator. See Sound level meter calibration and verification.

Instruments stating conformance

The table lists every instrument in the database whose manufacturer-published standards list mentions IEC 61252, including sound level meters with an optional dosimetry function, quoting the edition where the manufacturer states it. Intrinsically safe variants and exchange-rate options are shown on each instrument page and in the dosimeter table.