User`s manual

Section 4: Configure Inputs, Part II - Calibration Coefficients
38
Calibration Coefficients for A/D Count Sensors
For all calibration dialog boxes, enter the sensor serial number and calibration
date. Many sensor calibration equations contain an offset term. Unless noted
otherwise, use the offset (default = 0.0) to make small corrections for sensor
drift between calibrations.
Calibration coefficients are discussed below for each type of sensor:
temperature and strain gauge pressure sensor.
Temperature Calibration Coefficients
For SBE 16plus, 19plus, and 49:
Enter a0, a1, a2, and a3 from the calibration sheet.
Enter values for slope (default = 1.0) and offset (default = 0.0) to make small
corrections for temperature sensor drift between calibrations:
Corrected temperature = (slope * computed temperature) + offset
where
slope = true temperature span / instrument temperature span
offset = (true temperature – instrument reading) * slope; measured at 0 °C
Temperature Slope and Offset Correction Example
At true temperature = 0.0 °C, instrument reading = 0.0015 °C
At true temperature = 25.0 °C, instrument reading = 25.0005 °C
Calculating the slope and offset:
Slope = (25.0 – 0.0) / (25.0005 – 0.0015) = + 1.000040002
Offset = (0.0 – 0.0015) * 1.000040002 = - 0.001500060
Sea-Bird temperature sensors usually drift by changing offset, typically
resulting in lower temperature readings over time. Sea-Bird’s data indicates
that the drift is smooth and uniform with time, allowing users to make very
accurate corrections based only on pre- and post-cruise laboratory calibrations.
Calibration checks at sea are advisable to ensure against sensor malfunction;
however, data from reversing thermometers is rarely accurate enough to make
calibration corrections that are better than those possible from shore-based
laboratory calibrations.
Sea-Bird temperature sensors rarely exhibit span errors larger than ± 0.005 °C
over the range –5 to +35 °C (0.005 °C/(35 -[-5])C/year = 0.000125 °C/C/year),
even after years of drift. A span error that increases more than
± 0.0002 °C/C/year may be a symptom of sensor malfunction.
Pressure (Strain Gauge) Calibration Coefficients
For SBE 16plus and 19plus configured with a strain gauge pressure sensor,
and for all SBE 49s: Enter pA0, pA1, pA2, ptempA0, ptempA1, ptempA2,
pTCA0, pTCA1, pTCA2, pTCB0, pTCB1, and pTCB2 from the calibration
sheet. Offset is normally zero, but may be changed for non-zero sea-surface
condition. For example, if the in-air pressure reading is negative, enter an
equal positive value.
Notes:
• These coefficients provide
ITS-90 (T
90
) temperature.
• See Application Note 31 for
computation of slope and offset
correction coefficients from pre-
and post-cruise calibrations
supplied by Sea-Bird.
Note:
See Calibration Coefficients for
Voltage Sensors below for
information on strain gauge
pressure sensors used on other
instruments. See Calibration
Coefficients for Frequency
Sensors above for information
on Paroscientific Digiquartz
pressure sensors.