Heathus OMD, Manual

Page: 19 / 60

19
O
PERATING
P
ROCEDURES
60 minutes. The system is stable when the PPM readings
become consistant.
4) Press the CALIBRATION TEST button. The red LED above
the CALIBRATION TEST button will light up and a small
internal cell containing methane will be placed in the optical
path. This test cell will remain in the light path for approximately
five seconds unless the button is held down. After five seconds
the cell will return to its normal position and the red LED will
turn off. The increase in methane above the background should
be shown on the calibration data sheet that was shipped with
your instrument. In other words, if the baseline on the display at
the time of the calibration is 2 PPM and the calibration data
sheet indicates that the calibration cell contains the equivalent of
15 PPM of gas, an increase in signal level from 2 to 17 PPM
will be expected when the CALIBRATION TEST button is
pressed. Some deviation from this exact number is acceptable
as indicated by the range on the data sheet. It is good practice
to occasionally press the CALIBRATION TEST button during
the daily operation of the system to insure that the system is
operating properly.
The concentration of the gas within this test cell is actually
much higher than the reading listed on the data sheet. The
reading obtained from this test cell is equivalent to the read-
ing of a gas cloud that fills the entire volume within the light
path, that is, the volume between the lens on the lamp assem-
bly and the lens on the receiver assembly.
5) Set the Audible ALARM SETPOINT by pressing either the
ALARM SETPOINT UP or DOWN button. The audible
alarm will be sounded if the present methane level is greater
than the ALARM SETPOINT level. Holding either the up or
down ALARM SETPOINT button will enable the auto scroll