Xylem 6-Series Multiparameter - Manual (Page 85)

Sondes Section 2
YSI Incorporated Environmental Monitoring Systems Operations Manual 2-79
which characterize the new membrane and they MUST be entered via the Calibrate|Optic X – Dissolved
Oxy|Enter Cal Sheet selection as show above. Once the new constants have been entered in coded form
they will be transferred to the probe and will be visible in uncoded form in Advanced|Cal Constants.
See Section 5.9, Principles of Operation and Appendix M, ROX Optical DO Sensor for more
information.
User Calibration of the ROX Optical DO Sensor
NOTE CAREFULLY: As opposed to the 6562 Rapid Pulse Polarographic DO sensor described above,
there is no difference between the calibration routine for sensors which will be used for sampling or
monitoring applications. Usually the Autosleep RS-232 feature in the Advanced|Setup menu will be
activated for ROX calibrations, but there is no problem if it is not active.
Select the Optic X-Dissolved Oxy option from the Calibrate menu to calibrate the oxygen probe. The
submenu will offer you the option of calibrating in either percent air-saturation (ODOsat %) or oxygen
concentration (ODO mg/L) units. Calibrating either of the choices will automatically calibrate the other.
After selecting the option of choice (ODOsat % in water-saturated air or air-saturated water is normally
recommended), you will be prompted for the next step where you must elect to do either a 1-point or a 2-
point calibration. Except under unusual circumstances as described below, you should select the 1-point
option for the ROX Optical DO calibration.
Calibration Using Percent Air Saturation – 1-Point
NOTE: YSI recommends that you use this method for calibration of your 6150 Dissolved Oxygen Sensor
to obtain the maximum accuracy under normal operating conditions.
Place the sensor either (a) into a calibration cup containing about 1/8 inch of water which is vented by
loosening the threads or (b) into a container of water which is being continuously sparged with an aquarium
pump and air stone. Wait approximately 10 minutes before proceeding to allow the temperature and
oxygen pressure to equilibrate.
Select ODOsat % and then 1-Point to access the DO calibration procedure. Calibration of your Optical
dissolved oxygen sensor in the DO % procedure also results in calibration of the DO mg/L mode and vice
versa.
Enter the current barometric pressure in mm of Hg. (Inches of Hg x 25.4 = mm Hg).
Note:
Laboratory barometer readings are usually “true” (uncorrected) values of air pressure and can be used
“as is” for oxygen calibration. Weather service readings are usually not “true”, i.e., they are corrected to sea
level, and therefore cannot be used until they are “uncorrected”. An approximate formula for this
“uncorrection” (where the BP readings MUST be in mm Hg) is:
True BP = [Corrected BP] – [2.5 * (Local Altitude in feet above sea level/100)]
Press Enter and the current values of all enabled sensors will appear on the screen and change with time as
they stabilize. Observe the readings under ODOsat %. When they show no significant change for
approximately 30 seconds, press Enter. The screen will indicate that the calibration has been accepted and
prompt you to press Enter again to return to the Calibrate menu.
The minor advantages and disadvantages of calibration in air-saturated water versus water-saturated air are
outlined in Appendix M, ROX Optical DO Sensor