Xylem 6-Series Multiparameter - Manual (Page 83)

Sondes Section 2
YSI Incorporated Environmental Monitoring Systems Operations Manual 2-77
For the mg/L mode, calibration is carried out in a water sample which has a known concentration of
dissolved oxygen, usually determined by Winkler titration. For this calibration procedure, the sensor
should be immersed in the water. After thermal equilibration, enter the known mg/L value, press Enter,
and the calibration procedure will be carried out automatically as for the percent saturation mode above.
RAPID PULSE DISSOLVED OXYGEN WITH AUTOSLEEP OFF
If you intend to do Discrete Sampling, it is recommended that you turn Autosleep “off” in the
Advanced|Setup menu and follow these instructions for DO calibration. If you intend to do Unattended
Sampling, it is recommended that you turn Autosleep “on” and using the calibration instructions in the
preceding section.
Select the Dissolved Oxygen option from the Calibrate menu to calibrate the oxygen probe. The submenu
will offer you the option of calibrating in percent saturation or mg/L. After selecting the option of choice
(percent saturation in water-saturated air is normally recommended), you will be prompted for the next
step. Calibrating either of the choices will automatically calibrate the other.
For the percent saturation mode, be certain that the sensor has been thermally equilibrated in water-
saturated air and that the sensor has stabilized prior to beginning the calibration routine, particularly after a
membrane change. Relieve pressure in the cup if necessary. Remember, the Calibration Cup is designed to
be air-tight and must be loosened if used as a calibration chamber. Then follow the screen prompt and
enter the local barometric pressure in mm Hg, (inches Hg x 25.4), press Enter, and monitor the
stabilization of the DO readings. After no changes occur for approximately 30 seconds, press Enter to
confirm the calibration. Then, as instructed, press Enter again to return to the Calibrate menu. Note that at
calibration, the DOsat % (percent air saturation) value will reflect the barometer value that was entered.
For example, if a barometric pressure of 720 mm is entered, the DOsat % value will change to 94.7 %
(720/760 x 100).
Note that the parameter “DOsat %Local” is also available for users who prefer to set their percent air
saturation value to 100%, no matter what barometer value is entered. The method of activating this
parameter, its use, and its limitations are described in Appendix J of this manual. The key factor to
remember, however, is that no matter which convention (DOsat % or DOsat %Local) is selected, the mg/L
value will not be affected.
For the mg/L mode, calibration is carried out in a water sample which has a known concentration of
dissolved oxygen, usually determined by a Winkler titration. For this calibration procedure, the sensor
should be immersed in the water. After thermal equilibration, enter the known mg/L value, press Enter,
and the calibration procedure will begin with similar viewing of stabilization and confirmation of
calibration as for the percent saturation mode above.
NOTE: If you have resurfaced your DO sensor, we recommend running the probe continuously for 15-30
minutes or until good stability is realized. After only a membrane change (no resurfacing), run the probe
continuously for 3-4 minutes or until good stability is realized.
ROX OPTICAL DISSOLVED OXYGEN
Understanding the Factory Calibration of the ROX Optical DO Sensor
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