anx_VII__para__20
and must be equal for all kinds of opacimeters in order to give the same smoke value. Therefore, a Bessel filter has to be created in such a way, that the filter response time (tF) together with the physical (tp) and electrical response time (te) of the individual opacimeter must result in the required overall response time (tAver). Since tp and te are given values for each individual opacimeter, and tAver is defined to be 1,0 s in this Directive, tF can be calculated as follows:
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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.