Xylem 6-Series Multiparameter - Manual (Page 352)

ROX Optical DO Sensor Appendix M
YSI Incorporated Environmental Monitoring Systems Operations Manual M- 3
• The 6150 optical sensor has no flow dependence even in continuous operation during spot
sampling studies while the 6562 polarographic sensor can exhibit up to 3% flow dependence.
• For the 6562 polarographic sensor, users must calibrate the sensor by different methods for
sampling (Discrete Sample) and monitoring (Unattended Sample) by activating or deactivating the
“Autosleep RS-232” feature found in the Advanced|Setup menu. The calibration of the 6150
optical sensor is the same for both sampling and monitoring applications and no changes in the
“Autosleep RS-232” feature are required.
• It is possible to calibrate the 6562 polarographic sensor ONLY in oxygen-containing media at a
single point. The 6150 optical sensor can be calibrated at either a single point in oxygen-
containing media OR at two points, a zero-oxygen medium and an oxygen-containing medium.
This allows users to maximize the accuracy of the 6150 sensor at low oxygen levels if they feel it
to be necessary.
Is the ROX DO Sensor calibrated at YSI prior to shipment to the customer?
Yes. Factory calibration is required because, unlike all other sensors for YSI 6-series sondes, the response
of the ROX Optical DO sensor is not linear relative to the species being measured. This non-linearity
requires that the sensor be factory-calibrated at a number of oxygen values and the data fit to a third-order
regression. The three constants and the sensor value at zero dissolved oxygen which define this regression
analysis are automatically stored in the sensor at the time of factory-calibration. It is important to note that
these constants are a function of the sensor membrane installed on the 6150 probe and NOT a function of
the probe, i.e., the constants reflect the characteristics of the sensor membrane and NOT the probe. When
a 6150 probe is purchased from YSI, it already has a sensor membrane installed and the constants of that
membrane are transferred automatically to the sonde PCB when the sensor is run for the first time. After
transfer, the constants can be viewed by accessing the Advanced|Cal Constants menu as described below
in a separate question/answer.
Note, however, that, even with the factory calibration, the user still should perform a calibration after
receipt of the sensor as described below in order to assure that the typical accuracy specification is met.
How do I calibrate my ROX DO sensor?
The ROX DO sensor is typically calibrated in the same way as the YSI Rapid Pulse sensor – a single point
calibration in either air-saturated water, water saturated air, or a solution whose oxygen content has been
determined by Winkler titration. Like the Rapid Pulse sensor, the ROX sensor can be calibrated in either
the air-saturation mode (requiring a local barometer value input) or in concentration mode (requiring an
input of oxygen content in mg/L).
It is also possible to carry out a 2-point calibration of the ROX sensor with the other point being zero
oxygen content. NOTE, HOWEVER, THAT YSI DOES NOT RECOMMEND THE 2-POINT
CALIBRATION UNLESS (A) YOU ARE CERTAIN THAT THE SENSOR DOES NOT MEET YOUR
ACCURACY REQUIREMENTS AT LOW DO VALUES AND (B) YOU ARE OPERATING UNDER
CONDITIONS WHERE YOU ARE CERTAIN TO BE ABLE TO GENERATE A MEDIUM WHICH IS
TRULY FREE OF OXYGEN.
The calibration methods and recommendations for the ROX sensor are provided in detail in Section 2 of
this manual and in the instruction sheet which you received with the ROX probe. The key is to remember
that the single point calibration option will provide data of acceptable accuracy for the vast majority of
users and it should be used in most cases.