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Page 10 of 61
4.
PRINCIPLE OF OPERATION
The heart of the J405 is the well-proven gold film sensing technology. A thin gold film, in the
presence of mercury vapor, undergoes an increase in electrical resistance proportional to the mass
of mercury vapor in the sample.
When the SAMPLE button is pressed, an internal pump pulls ambient air through a scrubber filter
(AZI P/N: 600-0262) and into the flow system.
After three seconds, the sample solenoid bypass opens, closing off the scrubber filter from the
flow system.
The sample air passes through the AG filter (AZI P/N: 600-0293), an acidic gas filter that
removes any acidic gases that interfere with the sensor's response to mercury. Then the sample
air is drawn over the gold film sensor. The sensor adsorbs the mercury vapor. Eleven seconds
after starting, the sample solenoid bypass closes and the remainder of the sample is drawn through
the scrubber filter and the flow system. The instrument determines the amount of mercury
adsorbed and displays the measured mercury concentration on the digital meter in micrograms per
cubic meter (µg/m
3
) or milligrams per cubic meter (mg/m
3
) of mercury.
