Sea-Bird Electronics SBE 38, Руководство пользователя

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Manual revision 013 Section 5: Routine Maintenance and Calibration SBE 38
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Sensor Calibration
Sea-Bird sensors are calibrated by subjecting them to known physical
conditions and measuring the sensor responses. Coefficients are then
computed, which may be used with appropriate algorithms to obtain
engineering units. The temperature sensor on the SBE 38 is supplied fully
calibrated, with coefficients printed on the Calibration Certificate (see back of
manual). These coefficients have been stored in the SBE 38’s EEPROM.
We recommend that the SBE 38 be returned to Sea-Bird for calibration.
The primary source of temperature sensor calibration drift is the aging of the
thermistor element. Sensor drift is not substantially dependent upon the
environmental conditions of use, and — unlike platinum or copper elements
— the thermistor is insensitive to shock.
Sea-Bird’s Calibration Methodology
The SBE 38 is calibrated in Sea-Bird’s state-of-the-art calibration laboratory,
which maintains primary temperature standards (water triple point [TPW] and
gallium melting point [GaMP] cells), ITS-90 certified and standards-grade
platinum resistance thermometers, and a low-gradient temperature bath.
Temperature is computed using the Steinhart-Hart polynomial for thermistors
(Steinhart and Hart, 1968; Bennett, 1972), which is based on thermistor
physics. The equation characterizes the non-linear temperature versus
resistance response of the sensor. Note that thermistors require individualized
coefficients to the Steinhart-Hart equation, because the thermistor material is
an individualized mix of dopants:
t90 = 1.0 - 273.15 * Slope + Offset [°C]
a0 + a1 * [ln( n )] + a2 * [ln 2 ( n )] + a3 * [ln 3 ( n )]
where
n = SBE 38 raw output (counts).
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