Calculating A Response Factor - MSA Sirius Operating Manual

The response factor is defined as the ratio of the detector response for
isobutylene to the detector response for the sample gas. Response
factors for a wide range of substances have been determined
experimentally. These response factors are programmed into the
instrument. Note that the calibrated response curve, and all
programmed response factors are relative to isobutylene. (Isobutylene
has a response factor of one.)
The response factor is a multiplier that compensates for the difference
between the response of the sample gas and the response of
isobutylene. Whenever the monitor detects a signal, it uses the
response factor for that chemical to convert the signal to the correct,
displayed concentration of the sample gas (if its identity is known).
During calibration, this calculation is performed to define the calibrated
response curve. When sampling, the isobutylene equivalent response is
then multiplied by the response factor for the specific sample gas to
calculate the concentration.
If the response factor is known, you can use a monitor calibrated on
isobutylene to calculate the actual concentration of a target gas.
For example:
An operator is using a monitor that has been calibrated on isobutylene.
The sample gas is set to isobutylene. While using this instrument to
sample for hydrogen sulfide (H 2 S), the display reads 100 ppm. Since
the response factor for hydrogen sulfide is 3.46, the actual
concentration of hydrogen sulfide is:
Actual Hydrogen Sulfide concentration = 3.46 x 100 ppm = 346 ppm.

Calculating a Response Factor

To determine a response factor for a target chemical, perform the
following simple procedure:
1. Calibrate the Sirius Detector using isobutylene as the span gas.
2. On the monitor, set the sample gas name to isobutylene.
3. Apply a known concentration of the target chemical to the monitor
and note the concentration reported in the display.
4. The response factor for the target chemical relative to isobutylene:
RF target gas =
Concentration reported by instrument
Actual known concentration
2-3