Galvanic Applied Sciences ProTech903, Operation Manual

Page: 24 / 190

Revision 14
24 August 02, 2019
Figure 2-7: Sample Flow
Clean, humidified, and flow-regulated sample enters the sample chamber from the sample
inlet and passes over the Rate/Read Aperture strip, behind the rear window. Some of the gas
passes through the aperture strip and onto the lead acetate tape, causing a measurable color
change. The tape is held firmly against the sample chamber by the compression head. The
amount of gas that passes onto the tape is dependent on the size of the aperture strip. After
the gas passes over the tape, it is vented.
2.7.2 Read/Rate Aperture Strip
The Read/Rate aperture strip is used to control the quantity of gas that is actually passes
onto the lead acetate tape. If the H
2
S concentration in the sample gas is high, it may be
necessary to reduce the quantity of gas that passes onto the tape to react with the lead
acetate, otherwise the rate of color change will be too fast for the system to correctly analyze
the sample and poor results will be obtained. Likewise, if the H
2
S concentration in the sample
gas is low, it is necessary to allow more sample gas to pass onto the tape to allow the rate of
colour change to be high enough to produce reliable results. The size of the aperture in the
read/rate aperture strip is small for high concentrations, and for low concentrations it is large.
Certain ranges do not even require an aperture strip.
Galvanic Applied Sciences provides a broad range of read/rate aperture strip sizes. The most
common aperture strip sizes are listed in Table 2-1 along with the maximum ranges they are
capable of measuring and their correct part numbers. For other ranges, please contact
Galvanic Applied Sciences.