| motion within
the stack.
Isokinetic source sampling
is achieved when the velocity of gas entering
the sampling nozzle is exactly equal to the velocity
of the approaching gas stream. This provides a
uniform, unbiased sample of the pollutants being
emitted by the source. Isokinetic source sampling
most closely evaluates and defines various parameters
in the stack as they actually exist at the time
of sampling. Preliminary measurements are made
in order to determine the appropriate sized nozzle
for isokinetic sampling across the velocity profile
of the stack. Minor adjustments required to maintain
an isokinetic condition at each test point are
accomplished by regulating the sample flow rate.
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