Zeroing The Probe - Hach sension6 Instruction Manual

SECTION 3,
continued

3.3.3 Zeroing the Probe

With the probe in the calibration and storage chamber, observe
the mg/L dissolved oxygen concentration after the probe has been
polarized for the appropriate period of time. Calibration may be
performed when the display is stable for several minutes.
ion
Zeroing the sens
when measuring dissolved oxygen levels less than 1 mg/L or 10%
saturation. A new DO probe can generate a 0.02 to 0.05 mg/L
positive error in an oxygen-free (anoxic) solution. If this level of
error cannot be tolerated, zero the meter using the following
procedure. Also conduct this zeroing procedure after replacing
the sensing membrane or changing the internal filling solution.
1. Measure about 150 mL of sample or deionized water into a
250-mL beaker. Add a magnetic stir bar.
2. Add 0.25 g sodium sulfite or the contents of one Silica 3
Reagent Powder Pillow to the water. Stir to dissolve
the reagent.
3. Catalyze the reduction of dissolved oxygen by adding 0.1 mL
of a 1000 mg/L Cobalt Standard solution to the water.
4. Place the probe in the stirring sample for at least 10 minutes.
This solution is good for 30 minutes or more.
5. Press the key. The Cal icon will appear in the upper left
CAL
corner of the display, a flashing question mark will appear in
the upper right corner of the display, and the keypad icon will
appear in the lower left corner of the display.
6. Press the
READ ENTER
showing .
100%
7. Press the key on the keypad then press
0
8. The meter shows
the meter's zero DO criteria have been met it will return to
the read mode. The meter will not exit the zeroing routine
until the meter's zero criteria have been met.
38
6 Dissolved Oxygen meter is necessary only
key three times to skip to the display
while readings are taken. When
Stabilizing...
.
READ ENTER