Sea-Bird Scientific Deep SeapHOx V2, User Manual

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Calibration coefficients are stored in the sensor and are used with an on-board
temperature measurement and the user-selectable salinity constant to calculate pH from
the cell voltage potentials. The calculated pH value shows in each data frame sent from
the sensor.
Calibration coefficients are written to the header section of every raw .sbsdat data file that
uploaded from the sensor. The software uses these coefficients to re-process data.
7.10.2 Verify calibration
N O T I C E
Do not use NIST-type buffers with the sensor to check accuracy. The chemistry of those buffers is
not appropriate for marine pH measurements and can damage the external reference electrode.
The manufacturer recommends that the user monitor the accuracy of the calibration at
regular intervals. Compare the calculated pH values with independent pH data that is
collected just before and after a deployment, either in situ or from direct measurements of
a primary standard under temperature-controlled conditions.
One procedure for pre- and post-deployment checks is to start with a sample of known
pH and salinity (TRIS buffered synthetic seawater or other certified reference material).
The sensors require 20–40 psu.
1. Fill the flow cell with the sample. Close the opening and update the stored salinity
value with the sample salinity value: in the software, go to
Sensor , SeaFET , SeaFET
Settings , then Processing to enter the updated sample salinity value.
2. Make sure the sensor and a bottle of the additional sample is at a constant
temperature in a bath (e.g. overnight).
3. Flush the flow cell with the sample and then fill the flow cell. Return the sensor to the
bath. Record data until the values are stable and similar to the expected values. Do
not leave the standard TRIS recipe (it has no bromine) in the flow cell for extended
periods of time because it will start to change the chemistry of the external reference
electrode and void the calibration.
Maintenance
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