GMI PS500 Manual Del Usuario página 109

USER HANDBOOK
Response Factors
VOC detection by PID is dependent on the PID lamp used.
PS500 instruments incorporate a 10.6eV lamp, allowing a
large range of VOCs to be detected. However, the output
from a PID sensor varies according to the VOC detected
and consequently response factors are used to relate the
PID response of a particular VOC, to the PID response
of a calibration gas. The calibration gas used on PS500
instruments is usually isobutylene.
If the response of a PID to a particular VOC is eight times
smaller than it is for the same concentration of isobutylene,
then the response factor would be 8. Similarly, if the
response factor for a particular VOC is 0.5, the PID
response is twice that for isobutylene at the same
concentration.
Example:
• A PS500 is calibrated using isobutylene.
• Toluene is known to generate twice the response of
isobutylene.
If the PS500 is exposed to 100ppm toluene, the
•
instrument will read 200ppm.
To correct the PS500 reading, it is multiplied by the
•
response factor for toluene of 0.5 (see page B-11).
• If you know what VOC you are measuring, then the
following table will allow you to calculate the
concentration for your specific VOC. Note that these
are approximate values and for best accuracy you
should calibrate with the relevant VOC.
B-2