Defining The Response Factor; Table 4-2. Detector Counts - Thermo Scientific TVA2020 Instruction Manual

Calibration

Defining the Response Factor

Defining the
Response Factor
4-10 TVA2020 Instruction Manual
indication of when the reading has stabilized, or as a means of tracking the
repeatability of your calibrations.
You can also use these counts as an indication of the success of a
calibration. The "zero" counts are the counts expected when a zero gas is
applied to the detector. The span counts are the counts expected when a
span gas of known concentration is applied to the detector. Finally, the
detector sensitivity can be calculated by subtracting the zero counts from
the span counts and dividing by the span gas concentration. Use the
following general observations as a guideline:
Table 4–2. Detector Counts
Detector
FID
PID (10.6 eV lamp)
Example: A TVA2020 FID is calibrated with zero air and a 100 ppm
Methane in air span gas. The counts observed for the zero are 2895 and the
counts observed for the span are 27395. The span sensitivity is thus 245
counts/ppm [(27395-2750)/100 ppm]. Since both of these values (2895
zero counts and 245 detector sensitivity) are within the acceptable range,
the calibration is a good calibration. Examples of a bad calibration include
unusually high zero counts, or unusually low detector sensitivity. These
problems can often be attributed to poor calibration gases, contaminated
sampling accessories, a faulty detector capsule, or failure to follow the
proper calibration procedure. For more information, consult the
"Troubleshooting" chapter in this manual or contact Thermo Fisher
Scientific for assistance.
Although the FID and PID are calibrated with span gases of known
concentration (usually Methane and Isobutylene, respectively), both
detectors respond to many different compounds with differing levels of
sensitivity. In order to adjust the analyzer reading from "ppm of Methane"
or "ppm of Isobutylene" to ppm of the compound of interest, a correction
factor must be applied to the reading. This correction factor is also known
as a Response Factor. You can choose from up to nine (9) user-defined
response factors, or use the default response factor of 1.00. Each response
factor can be assigned a 9-character alphanumeric name.
The TVA2020 uses one of two different response factor formats: a
Multiplier or a Curve.
Zero Counts Detector Sensitivity
<6000 160-260 counts/ppm Methane
1000-2000 10-35 counts/ppm Isobutylene
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