YSI 600DW-B Sonde - Manual (Page 35)

Sondes Section 2
NOTE CAREFULLY: When calibrating a turbidity sensor for use with the 6920DW, you can use either the
standard calibration cup (with certain qualifications) or an optional extended length calibration cup. Please see
the section below which describes the special calibration recommendations for this sensor.
RECOMMENDED VOLUMES OF CALIBRATION REAGENTS
The approximate volumes of the reagents are specified below for both the upright and upside down
orientations.
Table 1
6920DW Sonde
Probe to Calibrate Upright Upside Down
Conductivity 200 mL 200 mL
pH/ORP 100 mL 250 mL
ISE 125 mL 275 mL
Turbidity, Chlorophyll, Rhodamine WT
w/ Standard Calibration Cup* 40 mL N/A
Turbidity, Chlorophyll, Rhodamine WT
w/ Extended Calibration Cup* 220 mL N/A
Table 2
600DW-B Sonde
Probe to Calibrate Upright Upside Down
Conductivity 50 mL 50 mL
pH/ORP 25 mL 50 mL
* See section below for special instructions dealing with calibration of the turbidity sensor with the two
types of calibration cup.
CALIBRATION OF THE 6136 TURBIDITY SENSOR
When used with the 6920DW sonde, the 6136 can be calibrated using two types of vessels:
• The standard calibration cup which was supplied with the sonde and which minimizes the volume of
calibration suspension required.
• An extended calibration cup which is designed to provide both the greatest accuracy and convenience,
but which requires the use of higher volumes of calibration suspension.
If you choose to calibrate with the standard calibration cup, you should engage only ONE THREAD when
screwing the calibration cup onto the sonde in order to keep the turbidity probe face as far as possible from
the calibration cup bottom to avoid interference. Even with these techniques, there will still be a small
interference from the bottom of the calibration cup that will cause your field turbidity readings to appear up
to 1 NTU lower than the actual reading. In many cases, this small error is negligible in surface water
studies, but can be important for drinking water studies where turbidity is generally very low. For
example, a true turbidity of 0.5 NTU could appear as a value of –0.5 NTU for drinking water and this is a
significant error.
The easiest way to avoid this error due to interference from the bottom of the calibration cup is to purchase an
optional, extended-length calibration cup for your 6920DW sonde (YSI Item Number 655488). Use of these
calibration cups completely eliminates bottom interference even when the calibration cup is completely
threaded onto the sonde. The only drawback to the use of the extended length cup is that its use requires
significantly higher volumes of calibration suspension. This factor is generally of no concern if you are
YSI Incorporated Drinking Water Monitoring Systems Operations Manual 2-28