Hanna Instruments HI 9142 User Manual

Page 12

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.

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.