YSI 6000UPG - Manual (Page 105)

6-5
point where plots of pH vs. mv at different temperatures intersect (the isopotential point) must be
known. Using standard pH determination protocol, the 6000
UPG software assigns the isopotential
point as the mv reading at pH 7 and then calculates the intercept using this assumption. Once the
slope and intercept to the plot of pH vs. mv are assigned at the new temperature, the calculation of
pH under the new temperature conditions is straightforward, and is automatically carried out by the
sonde software.
MEASUREMENT AND CALIBRATION PRECAUTIONS
(1) When filling the calibration cup prior to performing the calibration procedure, make certain that
the level of calibrant buffers is high enough in the calibration/storage cup to cover the pH probe and
temperature sensor of the 6030 probe.
(2) Rinse the sensors with deionized water between changes of calibration buffer solutions.
(3) During pH calibration, allow the sensors time to stabilize with regard to temperature
(approximately 60 seconds) before proceeding with the calibration protocol. The pH readings after
calibration are only as good as the calibration itself.
(4) Clean and store the probe according to the found in instructions found in Section 7 and
Appendix G of this manual.
6.5 DEPTH
The 6000
UPG
measures depth via a factory installed strain gauge sensor. The voltage output of this
device is directly proportional to the hydrostatic pressure exerted by the column of water over the
sonde. The 6000
UPG software converts this voltage to a depth reading in feet or meters via
calibration parameters which are factory installed. Readings are automatically compensated for the
density of the environmental medium which is estimated from the measured salinity.
CALIBRATION AND EFFECT OF TEMPERATURE
The depth sensor must be zeroed prior to deployment to account for atmospheric pressure. This
procedure is carried out by following the calibration menu instructions with the sonde in air only
(do not submerge). The temperature dependence of the sensor is automatically taken into account
by the sonde software based on input from factory calibration.
MEASUREMENT AND CALIBRATION PRECAUTIONS
(1) Be certain that the sonde is not immersed in water during the calibration procedure.
(2) Remember that the sensor which is currently available for the 6000 UPG is not vented. In
practical terms, this means that changes in barometric pressure after the sensor is initially calibrated
will appear as changes in depth. This effect is significant, particularly for the 0-30 ft option of the