HyQual Multi-probes User Manual v3, 08.07.2022
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7.3.7
Conductivity
HyQuest Solutions uses the four-electrode method to determine water conductivity. Two pairs of
graphite electrodes are situated in a stable geometry (you can barely see the electrodes; they look like
two bull’s eyes inside the slot on the conductivity sensor).
A constant voltage is applied to one of each electrode pair, and the amount of current required to main-
tain that voltage is measured. As the conductivity of the water increases, the current increases predicta-
bly.
Conductivity sensor maintenance is nothing more than occasionally cleaning the measurement surface
with a soft cloth or cotton swab and soapy water. Do not use anything abrasive.
The zero point for the sensor is set electronically, so you need only set the “slope” point:
1.
Open the Calibration menu and select
“SpCond µS/cm” or “SpCond mS/cm”, depending on your
preference of units.
2.
Screw your calibration cup onto the HyQual probe housing and remove the cup lid. Rinse your
sensors several times with the standard you’ll use for calibration.
3.
With the sensors pointed upward, fill the calibration cup until your solution covers the sensors
by an inch or so.
4.
Wait a few minutes for the temperature to equilibrate and the sensor to arrive at a steady read-
ing.
5.
Now just follow the calibration instructions on the screen.
The HyQual probe normally reports Specific Conductance
–
that’s Conductivity that has been standard-
ized to 25°C. Your reading is thus the conductivity of your water if that water was exactly 25°C. Conduc-
tivity has three other forms, Total Dissolved Solid
s (TDS), Salinity, and Resistivity (which we don’t report
because it has little meaning in natural waters). You can’t calibrate TDS or salinity directly because they
are calculated from Conductivity. You can, however, “calibrate” TDS with a TDS standard
by adjusting
the conductivity calibration point up or down until the TDS standard produces the desired TDS reading.
The same is true for Salinity if you’re using a standard quantified on the Practical Salinity Scale (PSS).
"Enable" TDS and/or Salinity by checking the box next to those parameters in the "Sensors and Parame-
ters" section.
7.3.8
pH
pH is measured as the voltage drop across the glass membrane of a pH electrode. A reference electrode
is used to complete the voltage-measuring circuit. The pH glass is specially formulated to absorb water
so that ions (particularly H+ and OH-) in the water are attracted to the glass to offset the ionic constitu-
ency of the pH electrode’s internal electrolyte. As a result, there is a charge separation across the glass,
and that’s the voltage we measure. pH readings are automatically compensated for temperature.
pH electrode maintenance is nothing more than occasionally cleaning the glass surface with a soft cloth
and soapy water. Do not use anything abrasive. The important part of pH maintenance is refilling the
reference electrode. (D.10)
You can choose a two- or three-point pH calibration. The two-point calibration, a seven buffer and a
second buffer whose value is near that of the waters you intend to monitor, is recommended. If you are
measuring in waters whose pH might range significantly above and below seven, you may be able to in-
crease your accuracy slightly by choosing a three-point calibration (seven buffers plus one basic buffer
and one acidic buffer). pH calibration is simple:
1.
Open the Calibration menu and select “pH”.
2.
Screw your calibration cup onto the HyQual probe housing and remove the cup lid. Rinse your
sensors several times with the standard you’ll
use for calibration.
