Xylem 6-Series Multiparameter - Manual (Page 315)

Turbidity Measurements Appendix E
YSI Incorporated Environmental Monitoring Systems Operations Manual E- 2
not recommend that you use tap water as the 0 NTU standard. For maximum accuracy at very low NTU
values (below the specification of the instrument), you may want to purchase turbidity-free water from YSI or
another vendor.
Should I carry out a 1-point, 2-point, or 3-point turbidity calibration, and what values should I use?
Even though the default calibration value in your sonde is reasonably appropriate for the “average” 6136
sensor, you need to carry out some multi-point calibration (2- or 3-point) prior to your first usage. This will
make certain that your system meets the YSI accuracy specifications provided in the operations manual.
For the accuracy required in most environmental applications, a 2-point calibration is sufficient, and it is
recommended that the two points be 0 and approximately 100 NTU – YSI offers a 126 NTU standard.
Only if you desire extreme accuracy in, for example, the 100-1000 NTU range, should you carry out a 3-
point calibration at 0, ca. 100, and ca. 1000 NTU. Note, however, that the effect on accuracy may be too
small to overcome the inconvenience of using the 3-point routine and the cost of the 1000 NTU standard.
Once the initial multi-point calibration of the 6136 sensor has been carried out, we recommend that the
accuracy of the sensor at low NTU be checked (or reset) by performing a 1-point calibration at 0 NTU
before each usage.
How often should I perform additional multi-point calibrations?
Your frequency of calibration will depend on the conditions under which your sonde is used and on the
degree of accuracy required in your application. Periodic calibration also confirms that the sensor is
performing properly with regard to its sensitivity and general function.
Our empirical testing has indicated that the optical system of the 6136 probe is very stable and likely to
require only infrequent calibration. However, you should initially confirm the stability of the sensor for
your typical sampling or monitoring application by frequently checking the sensor reading in a standard
other than 0 NTU prior to increasing the time between multi-point calibrations.
What color wiper should be used with my 6136 turbidity sensor?
The optimal wiper color for the 6136 depends on the software which is installed in the sonde. For versions
of 6-series software prior to 3.00, a white wiper should be used. For versions of software after 3.00, a
black wiper should be used. The difference exists due to an improvement in the wiper parking algorithm
which was implemented with Version 3.00 of software. If your sonde software version is pre-3.00, YSI
strongly recommends that you upgrade the software via the YSI Website and then use black wipers.
How do I purchase new wipers for the 6136 turbidity sensor?
Entire wiper assemblies, complete with installed pad, can be purchased from YSI in the 6627 Wiper
Replacement Kit (White) or the 6625 Wiper Kit (Black). If you wish to just change the pad on your old
wiper assemblies, you can purchase the 6144 Wiper Pad Kit from YSI.
What about data filter and spike rejection settings for processing turbidity data from the YSI
turbidity system?
As described in Section 5, Principles of Operation, some processing of raw turbidity data is usually
beneficial in terms of outputting values that reflect the “average” turbidity at the site. Filter options
designed to optimize this data processing are located in the sonde menu structure under both the 3-Sensor
and the 4-Data Filter selections in the 6-Advanced submenu.