Heath Consultants Optical Methane Detector (OM) - Manual (Page 31)

31
Chapter V
CALIBRATION CHECK
It should be noted that the OMD, like all survey instruments, is
not designed for absolutely accurate quantitative analysis. It is
designed for leak surveying. Its purpose is to find leaks as
small as one (1) PPM. The OMD has an accuracy rating of ±
10% within a range of 1 to 100 PPM. The accuracy drops to ±
20% within the range of 100 to 200 PPM. Above 200 PPM the
OMD is not relatively accurate.
If your OMD varies from calibration by more than ± 10%
within a range of 1 to 100 PPM there is something wrong with
the instrument, and it should be examined by a trained techni-
cian. The calibration of the OMD must be verified at the
beginning of each workday to insure the instrument is func-
tioning properly.
Verifying Calibration with Internal Check Cell:
Before verifying functionality of your OMD, the optical path
should be clean and aligned properly and the system should be
thoroughly warmed up (approx. one hour). The internal
check cell should be used on a daily basis to verify that the
functionality is remaining consistent. If the value of the
internal check cell should vary significantly (± 5 PPM) from
previous readings, your OMD might need to be calibrated.
However, the best approach is to use an external calibration
cell to verify calibration. This hermetically sealed cell can be
purchased as Heath P/N 100138-0. Below is a picture of this
cell.