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

Display Menus MI 611-185 – June 1996
The TVA-1000B uses one of two different response factor formats: a Multiplier or a Curve.
Response Factor Multiplier
A response factor multiplier is defined as follows:
Example: If 100 ppm of a compound produces an FID response of 50 ppm on an analyzer calibrated
with Methane, then the FID response factor would be 2.00 (100/50).
When using a response factor multiplier to correct a TVA-1000B reading, the analyzer multiplies
the reading by the response factor and displays the corrected reading. As in the example
give above, if a 50 ppm reading is obtained by the TVA-1000B, the analyzer would automatically
multiply 50 times 2.00 to get the actual concentration of 100 ppm.
Response Curve
Response Factor
=
----------------------------------------------------------
Actual Concentration
Measured Concentration
Response factors can change as concentration changes. The response factor for a compound
determined at 500 ppm may not be the same as the response factor determined at
10,000 ppm. By using a response curve, you can characterize a compounds response over a
broader range of concentrations. If the actual concentration is plotted as Y vs. X (measured
concentration), the resulting curve can be represented by the rational equation
Y = ----------------------------------------
AX
⎛1
+ -------------------------
BX ⎞
⎝ 10000ppm⎠
When using the RF Calc Mode “curve”, the terms A and B are entered into the TVA-1000B.
A represents the response factor multiplier at very low concentrations and B represents a
change to the response for every percent concentration increase.
The curve can only be defined by collecting response data at several different concentrations
and using a xy math spreadsheet to calculate the “best-fit” polynomial expression.
NOTE: Once the response curve has been fit, the calibration gas concentrations and
number of span points should not be changed without readjusting the curve fit.
To define and/or choose a response factor, choose 5=RF from the CALIBRATION menu.
The following display will appear:
RF0: Default
Up/Dn=Next RF
Enter=Accept
The top line shows the currently active response factor. If no response factor is applied, the
currently active response factor will be the factory DEFAULT (1.00 for FID methane and
1.00 for PID isobutylene). The name and value of the default response factor cannot be
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