Sea-Bird Scientific Deep SeapHOx V2, Руководство пользователя

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3.1 Ion-sensitive field effect transistor (ISFET)
The primary sensor element of the SeaFET
™
is the ISFET, a solid-state sensor that
senses pH in marine environments. The ISFET has two reference electrodes: an internal
reference and an external reference, that give separate reference potentials to the ISFET
and show separate pH values (pH Internal and pH External). After the corrections for
temperature and salinity are applied, the values from the internal and external are similar,
and let the user verify the validity of the sensor's measurements.
Internal reference
The internal reference electrode inside the DuraFET
®
is immersed in a bath of saturated
potassium chloride (KCl) gel and is physically separated frm the environment. The KCl
gel exposes the Ag/AgCl internal electrode to a relatively constant chloride concentration.
The sensor can therefore measure pH regardless of environmental salinity. If accurate
salinity and temperature data are not available, the internal cell is generally more
accurate.
External reference
The external reference electrode has a Ag/AgCl reference electrode in direct contact with
seawater. The potential of this electrode varies with pH and chloride concentration, so
unless the chloride concentration is known, the external reference is not stable. To
correct this, salinity can act as an approximation of chloride concentration. If accurate
salinity data is available, it can be applied to the pH external data and significantly reduce
measurement errors, and give the most accurate and stable pH data.
3.2 LED status indicator and batteries
The LED near the magnetic power switch shows the status of the sensor, so you can
determine if the sensor is in operation or ready to be deployed. To see the status of the
sensor, swipe the manufacturer-supplied magnet across the red circle at the top of the
magnetic switch. If the LED does not flash, verify that new batteries are installed and the
memory is configured. None of the settings on the SeaFET are affected when you use the
magnet to look at the status.
Product overview
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