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4.2 SENSOR PREPARATION / ACTIVATION
4.2.1 pH Preparation
Remove the shipping cap from the pH sensor. If the shipping cap does not contain
any liquid, pour HI 70300 into shipping cap, place it back on the sensor and
soak for at least 1/2 hour before use. If HI 70300 is not available, pH 4.01
buffer may be substituted.
4.2.2 ORP Activation
For improved redox measurements, the surface of the sensor must be clean and
smooth. A pretreatment procedure should be performed to ensure quick response.
The pretreatment of the sensor is determined by the pH and the ORP potential
values of the sample. Use the table below to determine the treatment required.
First locate the typical sample pH. If the corresponding ORP value (mV) is higher
than the values in the table below, an oxidizing pretreatment is necessary. If the
value is lower, a reducing pretreatment is necessary.
pH mV pH mV pH mV pH mV pH mV
0 990 1 920 2 860 3 800 4 740
5 680 6 640 7 580 8 520 9 460
10 400 11 340 12 280 13 220 14 160
For reducing pretreatment: immerse the electrode for at least five minutes in
HI 7091.
For oxidizing pretreatment: immerse the electrode for at least five minutes in
HI 7092.
Chapter 4 - PROBE INSTALLATION
4.1 SENSOR DESCRIPTIONS
HI 769828-0
Combination pH sensor features a glass pH
sensitive bulb and a silver/silver chloride double junction
reference with gelled electrolyte.
HI 769828-1
Combination pH/ORP sensor features a glass
sensitive bulb for pH readings, a platinum sensor for redox
measurements and a silver/silver chloride double junction
reference with gelled electrolyte.
Note See section 4.2.1 for pH preparation.
See section 4.2.2 for ORP activation.
HI 769828-2 Galvanic dissolved oxygen (D.O.) sensor. The
thin gas permeable membrane isolates the sensor elements
from the testing solution but allows oxygen to pass through.
The oxygen that passes through the membrane is reduced
at the cathode and causes a current, from which the oxygen
concentration is determined. The D.O. sensor conforms to
Standard Methods 4500-AG, EPA 360.1.
Note The D.O. sensor needs to be activated before instal-
lation. See section 4.2.3 for details.
HI 769828-3 4 ring-electrode conductivity (EC/TDS/Resistivity/
Salinity) sensor. The sensor is immune to polarization or surface
coatings.
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