Thermo Scientific TVA-1000B Instruction Manual - Geotech ...

Theory of Operation MI 611-185 – June 1996
UV SOURCE
LAMP
IONIZATION CHAMBER
WINDOW
METER
SAMPLE IN
SAMPLE OUT
COLLECTING
ELECTRODE
Dual Detectors
Figure 3. Typical Photoionization Detector
The benefits of each individual detector are very clear: both the FID and the PID have their
advantages and disadvantages. However, with either detector alone, the number of organic
and inorganic vapors that one can detect is limited by the measurement capabilities of that
detector.
With the TVA-1000B, users can obtain complete information about more organic and inorganic
vapors more quickly and easily than with single detector technology alone.
Since both detectors may be displayed and logged simultaneously, the relative response of the
two detectors may give some clues about the identity of the compound being measured. For
instance, the PID does not respond to methane at all, but the FID responds very well. A high
FID reading with virtually no PID response might indicate the presence of methane. Consequently,
PIDs respond very well to some inorganic gases that FIDs cannot detect. A high PID
reading with no FID reading might suggest the presence of an inorganic compound. With
readings from both detectors readily available, the TVA-1000B can help a user make decisions
about the type of compound present and which detector reading to use.
Benefits of Dual Detectors
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Cost-effective packaging
Detector response ratios can help characterize compounds
Enhanced analytical capability derived from simultaneous detection
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