Hach Ultra ORBISPHERE 3624, Operator'S Manual

Page: 64 / 102

58 of 96 Calibrations - 3624 ProBrix Plus
Operator Manual
ORBISPHERE
5.1.2.2 Fraction Calibration
In this calibration procedure, you must expose the sensor to a gas of known CO
2
purity,
at atmospheric pressure. This method uses the indicating instrument's internal
barometric pressure sensor as a reference.
Shut off sample flow to the sampling module, then open the sampling module front panel
and remove the CO
2
sensor from its flow chamber. Do not disconnect the cables or
purge gas connections from the sensor. Make sure that the grill in the front of the CO
2
sensor is clean and dry. Insert the sensor in the optional model 32001 flow chamber, and
tighten with its collar.
Connect a source of pure CO
2
to the central entry port of the flow chamber. Fully open
the exit from the flow chamber, thus making the gas pressure equilibrated with that of the
atmosphere.
To expose the sensor to the CO
2
gas and to stabilize the reading, operate in
Measurement Mode
for about 30 minutes. When stable, press
ESC
and select
CALIBRATE
from the main menu.
Select
SENSOR CO2
, followed by
FRACTION
. Select your preferred unit of
measurement from the
CO2 UNITS
menu, to bring up the menu for specifying the gas.
Enter the concentration of the calibration gas in volume percent and proceed as
described above for Partial Pressure Calibration.
Note:
If the sensor voltage slope shifts more than 1%, calibration restarts and the message
Recal Err XXX%
will appear. Three continuous calibrations with a shift of less than 1%
must be performed, before the calibration can be completed.
5.1.2.3 Dissolved Calibration
This method requires a known concentration of CO
2
dissolved in liquid as a reference
sample, flowing in-line through the sample line.
Select
CALIBRATE
from the main menu, followed by
SENSOR CO2
and
DISSOLVED
.
Select your preferred unit of measurement from the
CO2 UNITS
menu, to bring up the
menu for specifying the gas pressure.
Enter the dissolved CO
2
concentration of the sample and proceed as described above
for Partial Pressure Calibration.