DIN EN 13821 pdf free download

DIN EN 13821 pdf free download. Explosion prevention and protection.
4 Test apparatus 4.1 Spark generation circuit Annex A describes some suitable forms of circuit for spark generation all of which shall have the following charac- teristics: a) inductance of discharge circuit: from 1 mH to 2 mH except when the data is to be used for the assessment of electrostatic hazards. Then the total inductance of the discharge circuit shall not exceed 25 μH; b) ohmic resistance of discharge circuit: as low as possible and not more than 5 S; c) electrode material: tungsten, stainless steel, brass, or copper; d) electrode shaft diameter: 2,0土0,5 mm; e) electrode shape: pointed; f) electrode gap:≥6 mm (minimum); g) capacitance of electrode arrangement: as low as possible. If the parasitic capacitance of the electrode system is significant compared with the discharge capacitance, it shall be taken into account; h) insulation resistance between electrodes: sufficiently high to prevent leakage currents. NOTE For low spark energies together with pointed electrodes a significant fraction of the energy in the capacitance can drain away as corona discharges prior to the spark discharge.
5 Test sample The minimum ignition energy decreases with decreasing particle size. Therefore, the particle size distribution shall be determined for the sample as tested and shall be indicated in the test report. The minimum ignition energy decreases with decreasing moisture content. Therefore the moisture content shall be determined for the sample as tested and shall be indicated in the test report. NOTE 1 Where the particle sizes of the material in the plant are not known, tests should be carried out on dust samples of particle sizes of less than 63 μm, for example. NOTE 2 The size of the dust particles can be reduced by the dispersion process. In cases, where this effect can be important, its magnitude can be evaluated by measuring the particle size distribution after dispersion (without ignition),. NOTE 3 Grinding can alter the particle shape and surface conditin, and sieving can alter the proportion of inert in the sample. A rough lassification of the shape of the dust particles may also be necessary (.spherical”, .flatr or .fibrous’). NOTE 4 Where the moisture content in the plant is not known, the sample should be carefully dried, for example at 50。C under vacuum, or at 75。C and atmospheric pressure until the sample mass has reached a constant value. The minimum ignition energy is a function of the dustair mixture dynamics/turbulence and the dust concentration. The minimum ignition energy shall be measured at the optimum dust concentration and the lowest turbulence level experimentally attainable. The turbulence level is reduced by extending the ignition delay time until as long a delay time as is feasible for the apparatus is determined. The optimum dust concentration and the lowest turbulence level cannot be obtained in one step. Therefore an iterative procedure is required of which the main steps are as follows: Step 1 Start with a value of ignition energy that will reliably cause ignition of a given concentration in air of the dust being tested. Reduce the spark energy in steps (e.g. by 50%) at the given dust concentration until the dust cloud does no longer ignite in any of 10 tests at a given energy. Step 2 Continue the procedure varying the dust concentration at the lowest energy found under step1. If for any dust concentration an ignition occurs, then repeat Step 1 at that concentration. Step 3 Repeat the procedure by this combination of spark energy and dust concentration vanying the delay time (turbulence) until the maximum energy (E1) is found where no ignition occurs.DIN EN 13821 pdf download.