Instrumentation & Measurement Magazine 26-1 - 61

Fig. 4. Seawater conductivity measurement experiment.
a digital temperature constant system. The seawater temperature
in the preset constant system is set to quickly raise the
seawater temperature to the preset temperature value by the
heating module and then continuously adjusted by the small
chiller to achieve a constant seawater temperature value with
an accuracy of up to 0.001 °C. The seawater temperature in
the experiments was adjusted in the range 5 °C to 35 °C, since
most seawater in the ocean is in this range. As the seawater
conductivity is measured at different temperature points
and then fitted, the more temperature points measured the
more accurate the fitted curve will be, and here seven temperature
points were measured (5 °C, 10 °C, 15 °C, 20 °C, 25 °C,
30 °C, 35 °C). The Hydrocat CTD (Sea-Bird Hydrocat Temperature,
Salinity and Depth (CTD) Analyser) developed by
Sea-Bird Electronics can measure changes in seawater conductivity
from 34.5 mS/cm to 65.5 mS/cm at different temperature
points, in steps of approximately 5 mS/cm.
research, and different seawater temperature and salinity conditions
can also affect the survival activities of fish and other
aquatic organisms in marine pastures.
To solve this detection problem, the seawater conductivity
measurement system was built in the laboratory, as shown in
Fig. 4. It consists of a dc power supply, a Tektronix oscilloscope,
a transmitting circuit board, a measuring coil, a six-and-a-half
digital meter, and a seawater constant-temperature experiment
barrel. Seawater obtained from the South China Sea for
measurement is held in an adjustable temperature constanttemperature
seawater bucket. The salinity of the seawater is
constant. By adjusting the seawater temperature, the conductivity
of the measured seawater changes continuously.
The seawater constant temperature bucket is composed
of three heating modules, a large chiller, a small chiller and
Conductivity Measurement Experiment and
Simulation Data
According to the different connection modes of the detection
coil, receiving coil and resonance capacitor, as shown in
Fig. 5 the seawater conductivity measurement system can
be divided into four topological structures. The connection
modes of the detection coil, the receiving coil and the resonance
capacitor at the transmitting end are series and parallel.
Therefore, the system can be divided into series-series (S-S),
series-parallel (S-P), parallel-series (P-S) and parallel-parallel
(P-P) structures.
The input current and output voltage of the measurement
system with the S-S structure are measured with a resonant
frequency of 413.5 kHz at different conductivities. The curve
Fig. 5. Four topological model diagrams.
February 2023
IEEE Instrumentation & Measurement Magazine
61

Instrumentation & Measurement Magazine 26-1

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