6.1.1. Calculation of filter response time and Bessel constants

Directive 2005/55/EC of the European Parliament and of the Council of 28 September 2005 on the approximation of the laws of the Member States relating to the measures to be taken against the emission of gaseous and particulate pollutants from compression-ignition engines for use in vehicles, and the emission of gaseous pollutants from positive-ignition engines fuelled with natural gas or liquefied petroleum gas for use in vehicles (Text with EEA relevance) · European Union

The required Bessel response time (tF) is a function of the physical and electrical response times of the opacimeter system, as specified in Annex III, Appendix 4, Section 5.2.4, and shall be calculated by the following equation: where: The calculations for estimating the filter cut-off frequency (fc) are based on a step input 0 to 1 in ≤ 0,01 s (see Annex VII). The response time is defined as the time between when the Bessel output reaches 10 % (t10) and when it reaches 90 % (t90) of this step function. This must be obtained by iterating on fc until t90-t10≈tF. The first iteration for fc is given by the following formula: The Bessel constants E and K shall be calculated by the following equations: where:

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Source: EUR-Lex (Cellar) · retrieved 2026-11-01 · Text as adopted (Official Journal); later amendments are not incorporated in this text.