PerkinElmer Photovac MicroFID, User Manual

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MicroFID Software Manual
The presence of substituted functional groups (amino, hydroxyl,
halogens) on a simple hydrocarbon reduces its combustion
efficiency and thus MicroFID’s sensitivity to the compound.
Methanol and chloromethane, for example are detectable with
MicroFID but not as well as methane. A greater number of carbon
atoms can offset this loss of sensitivity due to substitution. For
example, MicroFID is more sensitive to n­butanol than it is to
methanol. See Response Factors on page 149 for a list of the
response factors of compounds detectable with MicroFID. The
information in this list is not a complete list of detectable
compounds. Contact the Applications Group for more information.
Calibration
Periodic calibration is required to compensate for FID output
changes due to inlet filter restriction, ionization chamber
cleanliness, sample pump wear and other factors.
During calibration, MicroFID is first exposed to zero air. A small
signal is generated. This zero signal is stored by the microprocessor.
MicroFID is next exposed to span gas. This span gas signal is stored
by the microprocessor. The microprocessor subtracts the zero signal
from the span gas signal and divides the difference by the user­
entered span gas concentration. The resulting sensitivity is stored in
the selected Cal Memory with the zero signal and the alarm level.
This number is then multiplied by the response factor and
displayed.
In High Sensitivity or sniff operation, you calibrate MicroFID with
zero gas only. The microprocessor subtracts the zero signal from the
MicroFID signal, and multiplies the difference by 1000. This
number is then displayed.
MicroFID readings are always relative to the calibration gas. After
calibration with methane, MicroFID will respond directly in units
equivalent to methane. Almost all combustible organic compounds
will be detected by MicroFID. It cannot distinguish between
methane and other ionizable compounds. A reading of 10 ppm
indicates all ionizable compounds that are present have generated
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