ISO 7240-20-2010 pdf free download

ISO 7240-20-2010 pdf free download.Fire detection and alarm systems — Part 20:Aspirating smoke detectors
Systémes de detection et dalarme d’incendie — Partie 20: Détecteurs de fumée par aspiration.
manufacturer’s instructions. If these instructions describe more than one method of mounting, then the method considered as the most unfavourable shall be chosen for each test.
5.1.4 Tolerances
Unless otherwise specified, the tolerances for the environmental test parameters shall be as given in the basic reference standards for the test (i.e. the relevant parts of IEC 60068-2).
If a specific tolerance or deviation limit is not specified in a requirement or test procedure, then a deviation limit of ± 5 % shall be applied.
5.1.5 Measurement of response threshold value
5.1.5.1 General
There are a number of different a.s.d. operating principles, which have different ranges of sensitivity. Accordingly, various methods can be used to measure the r.t.v. The object of any method chosen shall be to determine a measure of the aerosol concentration that, when passing through the detector, just causes the release of an alarm. This can generally be achieved by introducing smoke or an aerosol into the sampled air stream so that the detector is subjected to a slowly increasing concentration, and recording the concentration at the moment when an alarm is released. The r.t.v. is used only as a relative measurement: therefore, various parameters to measure the aerosol concentration may be used, providing that the chosen parameter is essentially proportional to the particle-number concentration (ie. a linear relationship) for the particular test aerosol. Further information is provided in Annex A.
5.1.5.2 Typical r.t.v. measurement procedure
Connect the specimen to measuring apparatus as recommended in Annex A. Control the airflow through the detector at a typical rate within the manufacturer’s specification.
Connect the specimen to the supply and monitoring equipment in accordance with 5.1.2 and allow it to stabilize for at least 15 mm unless otherwise specified by the manufacturer.
Before commencing each measurement, purge the measuring apparatus and specimen sufficiently to ensure that the result is not affected by the previous measurements.
Increase the aerosol concentration at an appropriate rate, depending upon the sensitivity of the specimen. The rate of increase In aerosol density shall be similar for all measurements on a particular a.s.d. type. It is recommended that the alarm signal be released at between 2 mm and 10 mm after the start of the test.
NOTE Preliminary testing can be necessary to determine the appropriate rate for a particular detector type.
The r.t.v. N shall be taken as the aerosol concentration at the moment when the specimen releases an alarm signal. The particular measuring unit for the aerosol concentration depends on the measuring apparatus used.ISO 7240-20-2010 pdf free download.