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

MI 611-185 – June 1996
Display Menus
The second line of the display shows what option is currently selected. If “Manual” is chosen,
after a calibration value has been accepted the instrument will prompt the user to decide
whether to save the calibration value or repeat the calibration (1 = Yes or 2 = Again?). If
“Auto” is chosen, the instrument will automatically store the accepted calibration value without
prompting the user.
RF Calc Mode
This selection allows you to choose how response factor correction will be applied to the reading.
Choosing this selection from the CAL CONFIG MENU produces the following display:
RF calc Mode:
Factor
1=Factor 2=Curve
The second line of the display shows what option is currently selected. If “Factor” is chosen,
the TVA-1000B will use a single constant response factor which is multiplied by the reading.
If “Curve” is chosen, the TVA-1000B will use a two constant equation. For more information,
refer to the section of the manual on “Response Factors.”
Detector Counts
Detector counts are the raw, unscaled detector output values associated with a gas measurement
performed by the FID or the PID. Before a detector reading is displayed or recorded, the
detector signal is converted from analog to digital. The result is a raw number, or A/D counts.
When a detector is calibrated, the detector counts for the zero gas and each of the span gases
are saved in memory. These detector counts are then used as reference points for calculating
the concentration values to be displayed or stored.
When calibrating the TVA-1000B in the “Manual” accept mode, the counts from the last calibration
(Zero or Span) are displayed before the calibration process is initiated. Once the calibration
process is initiated, the live detector counts are then displayed. You can refer to these
counts as an 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:
Detector Zero Counts Detector Sensitivity
FID 2000-4000 160-260 counts/ppm Methane
PID (10.6 eV lamp) 2000-20,000 3500-6000 counts/ppm Isobutylene
PID (11.8 eV lamp) 2000-20,000 300-900 counts/ppm Isobutylene
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