Owner's manual

10
11
TAKING MEASUREMENTS
Make sure the meter has been calibrated
and the protective cap has been removed.
Immerse the tip of the probe in the sample
to be tested.
Make sure the temperature sensor is also immersed.
For accurate dissolved oxygen measurements a water movement
of 0.3 m/sec is required at a minimum. This is to ensure that the
oxygen-depleted membrane surface is constantly replenished. A
moving stream will provide adequate circulation. To quickly check
if the water speed is sufficient, wait for the
reading to stabilize and then move the D.O.
probe. If the reading is still stable, the
measurement conditions are right, while if
the reading increases the water movement
is not adequate.
During field measurements, this condition may be met by manually
agitating the probe. Accurate readings are not possible while the
liquid is at rest.
During laboratory measurements, the use of a magnetic stirrer to
ensure a certain velocity in the fluid is recommended. In this way,
errors due to the diffusion of the oxygen present in the air in the
solution are reduced to a minimum.
At all times, time necessary for thermal equilibrium to occur
between the probe and the sample must be allowed (a few minutes
for temperature difference of several degrees).
SLOPE CALIBRATION
It is suggested to perform the slope calibration in satured air
(100% DO).
• Rinse the probe in a large amount of clean water to remove any
residual zero oxygen solution.
Dry the probe tip and allow a few minutes for the LCD readout
to stabilize.
• Press the CAL key and follow the indication
on the display.
• Adjust the slope trimmer on the bottom
of the meter to read “100%“ on the LCD.
Note:
• The slope calibration screw is located on
the bottom of the case.
• Press the CAL key and the LCD will
display the value in mg/L of oxygen.
A zero calibration is also possible.
ZERO CALIBRATION
• Dip the probe into HI 7040 zero oxygen
solution and stir gently for 2-3 minutes.
• Press and hold down CAL key then press
ZERO key.
• % tag will blink until the reading stabilize.
• When the reading is stable, the message “Press CAL, ...., meter
is calibrated“ will be displayed.
• Press CAL to exit zero calibration.
The zero calibration
of the HI 9142 is very stable, therefore this
procedure needs only to be performed whenever the probe is
replaced.
However, because the slope calibration is more critical, it is
recommended to perform this procedure every week.