ENMET MED AIR 2000, Operation And Maintenance Manual, Page: 17 / 30

M
ED
A
IR
2000 ENMET Corporation
13
5.1.2 Automatic Zeroing
A valid key entry sets the instrument in the " run AUTOMATIC ZEROING " position, which enables the setting of the
zero gas concentration point. This is desirable if the zero reference of one of the sensors has drifted over time. For
CO, the zero reference point is 0000 ppm CO; the zero reference point for oxygen is 20.9% oxygen by volume. Note
that the calibration procedure described in section 5.1.3 also includes setting the zero point. If a full calibration is
required, instead of setting just the zero point, press the
OPTION switch once; " run FULL CALIBRATION " is
displayed. See section 5.1.3.
T
O SET THE ZERO POINT WITHOUT PERFORMING FULL CALIBRATION
:
ƒ From the " run AUTOMATIC ZEROING " position, see flow chart.
ƒ Press the
SELECT
button; "
ATTACH ZERO GAS
" is displayed.
N
OTE
:
While it is possible to zero the sensor(s) using a sample from a "clean" air line, this entails using the sample as
a standard, and is best avoided. The best zero gas is a cylinder of 20.9% oxygen in nitrogen with no CO
present. This is available in the calibration kit listed in section 6.0
Pressing the OPTION switch at this point aborts the procedure and transfers the display to the " exit MAINTENANCE
MODE " position.
From Valid Key Entry
Example: Automatic Zeroing Flow Chart
T
O CONTINUE THE PROCEDURE
:
attach a cylinder of zero gas to the Calibration Port using the calibration adapter, as
shown in Figure 7 . Open the cylinder valve, set the regulator at 55
PSIG
, and turn the red handle of the sample-
calibrate valve up toward the calibration port. Let the gas flow for about a minute
ALARM
ACKNOWLEDGE
AUDIO
DEFEAT
FAULT
POWER
SELECT OPTION
Figure 7: Connection of Calibration Gas Cylinder
Cylinder of Gas
Cylinder Valve
and Regulator
Calibration Port
Sample/Calibration
Valve –
Up to Calibrate
O
To Full Calibration
Valid
Invalid
O
S
S
ATTACH
ZERO GAS
run AUTOMATIC
ZEROING
ZERO=30 .00V
20.9 130 00.0
Exit Maintenance Mode
Return to Operational Display
Return to Operational Display
with
“Fault 01” in place of the PPM reading
O = Option Switch
S = Select Switch