37
to scroll through the setup options until you
reach the combustible sensor screen.
(2) Press the “+” or “-“ keys to change the
combustible from reading in LEL to reading in
CH4.
(3) Press and hold the “CAL” key to save changes.
Note: Once the combustible sensor reading has
been changed to %CH4, it will appear as such in
all modes until it is changed back to reading in
LEL.
4.3.9.1 Calibrating the combustible sensor in
CH
4
mode.
With the PhD Ultra configured in the volume %
methane (CH
4
) mode, the LEL sensor will also be
calibrated to the actual volume percent methane
used in Biosystems calibration gas cylinders, not the
%LEL value given on the label. The actual volume
% CH
4
will be stamped on the side on the cylinder
body with indelible ink. For example, Biosystems
popular all-in-one mix of 54-9044E, with 50% LEL
propane equivalent will list 1.62% CH
4
on the
cylinder body. For easy reference, the actual
volume % CH
4
for the following Biosystems LEL
component mixtures is listed in the following table.
LEL Component
Description
Volume %
Methane (CH
4
)
50% LEL Methane
2.50
50% LEL Propane
Equivalent
1.62
50% LEL Pentane
Equivalent
1.25
Table 4.7.2.1 Percent LEL versus volume percent
methane for Biosystems calibration gas cylinders.
4.3.10 Calibration gas concentration
Calibration gas concentration values may be viewed
and adjusted through the instrument set up screens.
Calibration values shown in
the calibration value table must match those
appearing on the calibration gas cylinder(s) that
will be used to calibrate the PhD Ultra. Non-
matching calibration gas and calibration gas
value settings will lead to inaccurate and
potentially dangerous readings.
To adjust the calibration gas concentration:
(1) Move to the “Instrument Setup” screen as
described in section 4.3.1 and use the ‘CAL’ key
to scroll through the setup options until you
reach the “Calibration Gas” screen
If an LEL combustible gas sensor has been
installed, the LEL sensor’s calibration gas
concentrations will be the first shown.
This screen indicates the concentration and type
of test gas that will be used to calibrate the
instrument. In the example above the screen
indicates that “50 % LEL span gas” will be used.
(2) Use the “+” and “-” buttons to change the
concentration of the gas that will be used.
Calibration values shown in
the calibration value table must match those
appearing on the calibration gas cylinder(s) that
will be used to calibrate the PhD Ultra. Non-
matching calibration gas and calibration gas
value settings will lead to inaccurate and
potentially dangerous readings.
(3) Press the “CAL” button to advance to the
calibration gas that will be used for the next
sensor currently installed. Once again, use the
“+” and “-” buttons to make a change in the
concentration of the calibration gas that will be
used.
(3) Press and hold the “CAL” key to save changes.
4.3.10.1
“CO Plus” sensor calibration gas
screen
The “CO Plus” sensor may be calibrated to either
hydrogen sulfide or carbon monoxide.
Do not use multi-component
calibration gas mixtures containing both carbon
monoxide and hydrogen sulfide when
calibrating a PhD Ultra with a CO Plus sensor
installed. Calibration of the CO Plus sensor
with multi-component calibration gas mixtures
containing both CO and H
2
S may lead to
inaccurate and potentially dangerous readings.
Biosystems multi-component calibration gas
mixtures containing both carbon monoxide and
hydrogen sulfide are labeled as “Not for use
with CO Plus sensors”.
With the CO Plus sensor, the
calibration gas setting determines whether the
instrument is configured for the direct reading
of CO, or for the direct reading of H
2
S.
Calibration gas corresponding to the direct
reading requirement must be used in the
calibration of the instrument. If carbon
monoxide is chosen in the calibration gas
setting option, the display will show CO+ and
carbon monoxide must be used to verify
accuracy. Similarly, if hydrogen sulfide is
