YSI 6000UPG - Manual (Page 102)

6-2
MEASUREMENT AND CALIBRATION PRECAUTIONS
(1) When filling the calibration vessel prior to performing the calibration procedure, make certain
that the level of calibrant standard is high enough in the calibration cup or beaker to cover the entire
conductivity cell (approximately 500 mL).
(2) After placing the sonde in the calibration solution, agitate the sonde to remove any bubbles in
the conductivity cell.
(3) During calibration, allow the sensors time to stabilize with regard to temperature (approximately
60 seconds) before proceeding with the calibration protocol. The readings after calibration are only
as good as the calibration itself.
(4) Perform sensor calibration at a temperature as close to 25 o C as possible. This will minimize
any temperature compensation error.
6.2 SALINITY
Salinity is determined automatically from the 6000 UPG conductivity readings according to
algorithms found in Standard Methods for the Examination of Water and Wastewater (ed. 1989).
The use of the Practical Salinity Scale results in values which are unitless, since the measurements
are carried out in reference to the conductivity of standard seawater at 15 C. However, the unitless
salinity values are very close to those determined by the previously used method where the mass of
dissolved salts in a given mass of water (parts per thousand) was reported. Hence, the designation
“ppt” is reported by the instrument to provide a more conventional output.
6.3 OXIDATION REDUCTION POTENTIAL (ORP)
The 6000 UPG determines the Oxidation Reduction Potential (ORP) of the media by measuring the
difference in potential between an electrode which is relatively chemically inert and a reference
electrode. To measure ORP with the 6000
UPG , a combination an ORP probe must be in place in the
ISE2 port of the sonde bulkhead and ORP must be activated in both the sensor and report setups.
The ORP sensor consists of a platinum ring found on the tip of the probe. The potential associated
with this metal is read versus the Ag/AgCl reference electrode of the pHsensor in the ISE1port
Thus, to read ORP you must also have a pH probe installed. ORP values are presented in millivolts
and are not compensated for temperature.
CALIBRATION AND EFFECT OF TEMPERATURE
Calibration is required infrequently for the ORP sensor of the 6000 UPG . However, after long term
use of the pH and ORP probes some deviation from the theoretical ORP value may occur. This
deviation is usually due to a change in the concentration of the KCl in the reference electrode gel
and can be “calibrated out” using the sonde software involving ORP calibration. However, the