INFICON MicroFID II Portable Flame Ionization Detector - Manual (Page 58)

074-579-P1A 58
MicroFID II Calibration
Calibration Technical Description
The MicroFID II will always detect all ionizable compounds present in a sample regardless of
the response factor (RF) selected.
NOTE: Even if the MicroFID II has been calibrated with a specific compound, its response is not
specific and the presence of another ionizable impurity may render the numerical result invalid.
It is often impractical to carry a range of different standards into the field. Approximate results
can be obtained by calibrating the MicroFID II with the recommended span gas and entering the
appropriate response factor. The response factor is based on the ratio of the response of the
specific compound to the response of the span gas. The response factor multiplies the MicroFID
II
’S reading, then displays and records it.
NOTE: The MicroFID II is a total VOC instrument and will ALWAYS respond to all ionizable
compounds present in a sample. The MicroFID II will NOT respond only to a specific compound
if an RF is programmed. It is the responsibility of the user to be aware of the limitations of Flame
Ionization Detection instruments.
Calibration is required for the MicroFID II to compensate for temperature/climate changes as
well as output changes due to inlet filter restrictions, ionization chamber cleanliness, sample
pump wear and other factors. It is also needed in order to display concentration in ppm units
equivalent to the calibration gas.
During calibration, the MicroFID II is first exposed to zero air which contains no ionizable gases
or vapors. It is used to set the MicroFID II
’s zero point. A small signal is generated and the zero
signal is stored by the microprocessor.
MicroFID II 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.
MicroFID II readings are always relative to the calibration gas. After calibration with a span gas,
MicroFID II will respond directly in units equivalent to that span gas. Almost all combustible
organic compounds will be detected by MicroFID II. It cannot distinguish between the selected
calibration gas and other ionizable compounds. A reading of 10 ppm indicates all ionizable
compounds that are present have generated an ion current proportional to 10 ppm of the
selected calibration gas. MicroFID II readings give an indication of the total ionizables present
and their concentration relative the calibration gas.
Due to the MicroFID II
’s sensitivity, outdoor air is usually unsuitable for calibration. A charcoal
filter (Part No. MX396022) may be connected to the instrument to produce clean air from
otherwise unsuitable ambient air. For best results, use a commercial source of zero grade air
and a second sampling bag. Zero air should have not more than 0.1 ppm total hydrocarbons
(THC).