YSI 600DW-B Sonde - Manual (Page 228)

Principles of Operation Section 5
NOTE: Before calibrating your 6136 turbidity sensor, pay particular attention to the following caution:
• For all calibration procedures, you MUST use standards that are based on either formazin or AMCO-
AEPA styrene divinylbenzene beads as described in Standard Methods for the Examination of Water
and Wastewater and have been prepared either by Hach (formazin based) or AMCO-AEPA based
standards prepared by YSI or an approved YSI vendor listed on the YSI website (www.ysi.com). THE
USE OF STANDARDS FROM OTHER VENDORS AND/OR THOSE PREPARDED FROM
MATERIALS OTHER THAN FORMAZIN OR AMCO-AEPA POLYMER BEADS WILL RESULT
IN BOTH CALIBRATION ERRORS AND INACCURATE FIELD READINGS.
YSI and its approved vendors offer easy-to use AMCO-AEPA turbidity standards which can also be
quantitatively diluted with turbidity-free water to provide calibrant suspensions of lower values. Hach also
offers relatively inexpensive formazin suspensions at various NTU values up to 1000 NTU under the
Stablcal
TM designation which will provide accurate calibration of either the 6026 or 6136 sensors as long as
the user is willing to exercise the proper safety precautions as outlined in the MSDS associated with formazin.
The primary advantage of the Hach formazin standards is their cost; their primary disadvantage is that the
suspended matter settles out fairly rapidly. Although the AMCO-AEPA standards are somewhat more
expensive, they do not settle out, making them significantly easier to use.
While the effect of temperature on the turbidity sensor is small, this factor is automatically taken into
account by the sonde software providing temperature compensated readings. Temperature coefficients of
0.3%/degree C and 0.6%/degree C are automatically activated for the 6026 and 6136, respectively, when
these sensors are activated in the Sensor menu.
MEASUREMENT AND CALIBRATION PRECAUTIONS
(1) For best results, use only freshly prepared or purchased turbidity standards. Degradation of standards
can occur on standing, particularly formazin prepared from dilution of concentrated suspensions such as
Hach 4000 NTU standard.
(2) If unusually high or jumpy readings are observed during the calibration protocol, it is likely that there
are bubbles on the optics. Manually activating the wiper of the 6026 or 6136 from a computer or 650
MDS keypad removes these bubbles.
(3) When calibrating the 6136 sensor, be aware of the fact that precautions must be taken to avoid
interference of the bottom of the calibration vessel. Instructions for two methods of calibrating the 6136
sensor are provided in Section 2.6.1 of this manual. The best solution to the interference problem,
however, is to purchase the 655488 Extended Calibration Cup Sleeve which completely eliminates the
issue.
The sonde turbidity system allows the user to either observe these real turbidity events (while obtaining
somewhat jumpy readings) or to apply a mathematical filter to the raw data so that the NTU output may be
more reflective of the overall cloudiness of the environmental sample. From the Advanced|Data Filter
menu of the sonde software, the user can activate the data filter that is specific to turbidity and “fine tune”
its performance. For typical sampling and monitoring applications, YSI recommends that the Data Filter
settings be selected as follows: Enabled -- On; Wait for Filter -- Off; Time Constant = 12; Threshold =
0.010.
For most unattended sampling applications, selection of the above filter settings should also be appropriate.
However, an additional capability is also available which enhances the elimination of spurious single point
spikes from the logged data and thus allows for a better presentation of the average turbidity during the
deployment. This “Turb Spike Filter” is activated/deactivated in the Advanced|Sensor menu. Its
capability is further described in Section 2.9.8, Advanced. YSI recommends the use of this feature for all
YSI Incorporated Drinking Water Monitoring Systems Operation Manual 5-15