21
20
5. Measurement
Taking DO readings
During measurement, the probe can be:
• fully immersed in the solution
• partially immersed in the solution
Do not allow the probe’s membrane surface to touch
anything! The probe guard (the piece with holes fitted
over the end of the probe) protects the membrane; you
should leave this piece attached to the probe at all times.
IMPORTANT:
since the DO probe consumes oxygen from the sample, the sample
must constantly flow past the membrane to achieve more accurate readings. You can
use a stirrer to accomplish this (see “Accessories” on page 65 for a magnetic stirrer).
To take measurements:
1.
Rinse the probe well with deionized
rinse water or rinse solution.
2.
Select the appropriate measurement
mode. Press the MODE key
to toggle
between modes:
• % saturation.
• mg/l (ppm)**,
• pH
3.
Dip the probe into the sample.
Stir the
probe gently to homogenize the sample.
Make sure that the sample is continu-
ously flowing past the membrane sensor.
4.
Note the reading on the display.
If the
READY indicator is switched on, it will
appear when the reading is stable.
See figure
ATC
READY
MEAS
C
mg/l
5.1
A
A
Probe guard
**To select between mg/l and ppm units, see page 52.
The ATC indicator should appear in the lower right hand corner of the display.
If it does not, this indicates an error.
CONTINUED ON NEXT PAGE
Taking measurements with READY indicator selected on
If the READY indicator has been activated, the READY annunciator lights when
the reading is stable. Switch the READY indicator on or off in the SETUP program
P5.1 for % saturation measurements (page 43) or program P4.1 (page 51) for mg/l
(ppm) measurements.
Taking measurements with the auto endpoint feature selected on
When a reading is stable for more than 5 seconds, the auto endpoint feature will
automatically “hold” the reading. The “hold” indicator appears on the left side of
the display. Press the HOLD key to release the reading. Switch the Auto endpoint
feature on or off in the SETUP program P5.1 for % saturation measurements (page
43) or program P4.1 (page 51) for mg/l (ppm) measurements.
Taking pressure/salinity compensated DO measurements
If necessary, you can adjust the pressure and salinity values of your measurements
in the SETUP mode. The DO meter will automatically compensate for salinity and
pressure based on the values entered in the setup functions. The meter is factory set
at 760 mm Hg (101.3 Pascals) pressure adjustment and a factor of 0.0 salinity adjust-
ment. See Appendix 2 on page 67 for a “Pressure vs Altitude” table.
Pressure adjustment
NOTE: This adjustment appears in both
the % saturation and mg/l (ppm)
measurement modes.
1.
Press the MODE key
to select % satura-
tion or mg/l (ppm) mode. Press the
SETUP key
to enter Set Up mode.
See figure
2.
Press the ENTER key
until the upper
display shows a number and the lower
display shows “Hg” or “PA”.
3.
Use the
▲
and
▼
keys
to enter the
barometric pressure. The upper display
will show the value you have entered.
See figure
4.
Press ENTER
to confirm pressure value.
5.
Press CAL/MEAS to return to measure-
ment mode, or continue with step 4 on
page 22 to make a salinity adjustment
[available from mg/l (ppm) mode only].
5.2
SETUP
A
SETUP
B
A
B
