B FOREWORD
The OCEAN SEVEN 310 CTD multi-parameter probe automatically performs sensor data processing
functions needed to guarantee the probe measurement stated accuracy and precision. This section
briefly introduces the data processing procedures.
B.1 CTD MEASUREMENT SYNCHRONIZATION
Independently from the applied filtering procedure the OS310 data acquisition hardware and firmware
guarantee the simultaneous measurement of all sensors.
B.2 RAW DATA FILTERING
The aim of the “raw data filtering functions” is to attenuate the noise in the acquired data without
affecting the signal content. The OS310 is shipped with pre-set best condition and it should be noted
that modifying the raw data processing filtering can led the probe to deviate from the stated
measurement accuracy and/or precision. We discourage the modification of the raw data filtering.
B.2.1 Thermal compensation
The thermal compensation procedure is applied to the CTD (Conductivity, Temperature and Pressure)
sensors only. The thermal compensation algorithm compensates deviation of the electronic preamplifier
of the CTD sensors due to the variation of the ambient temperature inside the probe housing. The
thermal compensation is performed by continuously monitoring the probe internal temperature and by
applying a thermal compensation algorithm based on coefficients obtained in laboratory by means of
repeated thermal characterization cycles.
B.2.3 Temperature sensor self-heating minimizing
To eliminate the self-heating effect of the temperature sensor, the OCEAN SEVEN 310 probe powers
off the temperature sensor excitation when not needed. Without this precaution, the temperature sensor
itself is capable of changing the temperature of the small volume of water immediately around it by a
fraction of milli-degrees °C in the presence of a modest water flow.
B.3 CONVERSION INTO ENGINEERING UNITS
Raw data consists of digitised voltages or ADC counts acquired from the sensors through the electronic
sensor conditioning circuits (sensor preamplifiers). Raw data values are converted into physical and
chemical units by means of calibration data and data conversion algorithms.
B.2.1 Dedicated conversion procedure
Conversion of signals coming from a sensor into engineering units is the result of a processing algorithm,
which for some sensors cannot be directly correlated with a standard mathematical method. For such
parameters, a dedicated data conversion function is provided. The OCEAN SEVEN 310 has dedicated
processing algorithms for the following sensors:
❖ Dissolved oxygen sensor saturation.
❖ Dissolved oxygen sensor expressed in ppm.
❖ pH expressed in pH.
❖ REDOX expressed in mV
An overview of the processing algorithms and parameters is described in the introduction section.
B.2.2 Common conversion procedure
Sensors which do not require dedicated conversion procedure use polynomial (up to the 2
nd
order) or
first order interpolation algorithms to convert the ADC counts into engineering values.
Polynomial interpolation: y = a + bx + cx2 + dx3
1st order interpolation: y = a + bx
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