Xylem 6-Series Multiparameter - Manual (Page 91)

Sondes Section 2
YSI Incorporated Environmental Monitoring Systems Operations Manual 2-85
When selecting Optic X -6026-Turbidity (or 6136-Turbidity), there will be a choice of 1-point, 2-point,
or 3-point calibrations for your turbidity sensor.
The 1-point option is normally used to zero the turbidity probe in 0 NTU standard. Place the sonde in clear
water (deionized or distilled) with no suspended solids, and input 0 NTU at the screen prompt. Press Enter
and the screen will display real-time readings that will allow you to determine when the turbidity readings
have stabilized. Press Enter after the readings have stabilized to confirm the calibration and zero the
sensor. Then, as instructed, press any key to return to the Calibrate menu.
Select the 2-point option to calibrate the turbidity probe using only two calibration standards. In this case,
one of the standards must be clear water (0 NTU) and the other should be in the range of known turbidity
for the water to be monitored. For example, if the water to be evaluated is known to be low in turbidity, an
appropriate choice of standards might be 0 and 10 NTU (6026) or 0 and 12.7 NTU (6136). However, for
general purpose measurements an appropriate choice of standards is usually 0 and 100 NTU (6026) or 0
and 126 NTU (6136).
To begin the calibration, immerse the sonde in the 0 NTU standard, as instructed, and press Enter. It is
mandatory that the 0 NTU standard be calibrated first. The screen will display real-time readings that will
allow you to determine when the readings have stabilized. Pressing Enter will confirm the first calibration.
Following the instructions on the screen, place the sonde in the second turbidity standard, input the correct
turbidity value in NTU, press Enter, and view the stabilization of the values on the screen in real-time.
After the readings have stabilized, press Enter to confirm the calibration. Then, as instructed, press any
key to return to the Calibrate menu.
Select the 3-point option for maximum accuracy over the entire range of 0 to 1000 NTU. As for the 2-
point procedure, one of the standards must be 0 NTU. Because of the linearity characteristics of the
sensors, we recommend that the other two standards have turbidity values of 100 and 1000 NTU.
However, the user can select any values that are deemed appropriate. The procedure for this calibration is
the same as for a 2-point calibration, but the software will prompt you to place the sonde in the additional
solution to complete the 3-point procedure.
For all turbidity calibration procedures, be certain that the standard and sensor are thermally equilibrated
prior to proceeding with the calibration.
For further information related to setting up, calibrating and running turbidity measurements, refer to
Appendix E, Turbidity Measurements.
OPTIC CHLOROPHYLL
When selecting Optic X - Chlorophyll, there will be a choice of zeroing the relative fluorescence unit
parameter (Chl RFU Zero) or calibrating with actual chlorophyll standards (µg/L 1-point, 2-point, or 3-
point).
If you have selected Chl RFU as a parameter in the Report menu, the sonde will report only relative
values of fluorescence in the sample being measured. These values could then be converted into actual
chlorophyll concentrations in µg/L by using a post-calibration procedure, after the chlorophyll content of
grab-samples taken during a sampling or monitoring study has been analyzed in a laboratory. This
determination can involve conducting the extractive analysis procedure described for chlorophyll in
Methods for the Examination of Water and Wastewater
or by carrying out an in situ measurement of
chlorophyll using a commercial benchtop fluorometer.
The Chl RFU Zero option is used to zero the fluorescence probe in a medium that is chlorophyll-free.
Place the sonde in clear water, and input 0 at the screen prompt. Press Enter and the screen will display
real-time readings that will allow you to determine when the fluorescence readings have stabilized. Press