ASTM E:19 pdf download

ASTM E:2019 pdf download.Standard Test Method for Minimum lgnition Energy of a Dust Cloud in Air.
In order to make an ignition test, the high voltage electrode is grounded and the required mass of the prepared dust is placed in the dispersion cup. The dc voltage supply then is switched into the circuit. and as sparks start to pass between the electrodes, the powder is dispersed by an air jet. It is noted whether ignition occurs and flame propagates away from the spark gap.
X1.4.5 The first tests usually are performed with a high spark energy typically 500 mJ. If there is an ignition, the spark energy then is reduced in steps, and the test repeated until ignition does not occur, as described in II . 1.
Xl.5 Triggering by auxiliary spark, using normal two- electrode system (trigger transformer in discharge circuit).
X1.5.l Fig. X1.4 illustrates the spark generating circuit of the test apparatus.
X1.5.2 The basic circuit described by Eckhoff (9, 11) has been adopted by several U.S. companies for routine dust MIE measurements, as discussed by Britton (10) . The diode “D” described by Eckhoff(9, 11) is omitted in some “routine MIE” circuit designs. A storage capacitor “C” is charged to voltage “Vi” as measured by a very high impedance (>1013 ohm) voltmeter such as a field-mill voltmeter. Voltage “Vi” is typically less than 2500 V and incapable of causing spark breakdown of the gap “G”. When “C” is fully charged, the stored energy W=0.5CV12. To effect spark breakdown, a “trigger” capacitor “CT1” is discharged through the primary of transformer “T” which results in a transient high voltage across the secondary and spark breakdown of gap “G”. When this occurs, the storage capacitor “C” partly discharges through the spark gap. If the voltage remaining on “C” = V1, the change in energy W (Joules) = 0.5C (V12— V2, where C is given in Farads and V in volts. The total energy discharged through the spark gap is assumed equal to W plus a minor contribution from trigger capacitor “Tr”• Various combinations of “C” and “Vi” allow the stored energy to be continuouslyvaried up to at least 1000 mJ. One such circuit (10) uses a switched bank of five capacitors (0.001, 0.01, 0.05, 0.1 and 0.5 iF) with a maximum voltage V1= 2500 V. The trigger capacitor “CTr” (0.471iF) IS initially charged to 165 V and is discharged through an automobile ignition coil producing an open-circuit secondary voltage of the order 13 kV. The energy initially stored on “CT1”is 6.4 mJ, hut in view of circuit losses (principally the transformer) the nominal contribution to spark energy is assumed to he 5 mJ for reporting purposes, that is, ignition energy W0(mJ) = 5 + 1000 W, Closure of switch “S” is electronically timed to coincide with formation of an optimized dust cloud. For routine measurements the optimum time delay.