Xylem 6-Series Multiparameter - Manual (Page 317)

Turbidity Measurements Appendix E
YSI Incorporated Environmental Monitoring Systems Operations Manual E- 4
How do I manually activate the turbidity wiper on a 6136 turbidity probe when the sonde is sampling?
If you are using the sonde with a 650, highlight the “Clean Optics” entry in the upper right logging box and
press Enter to activate the wiper. If the sonde is connected to a computer (sequential lines of data are
present on the screen), press the “3” key to activate the wiper.
What precautions should I take when using the sonde turbidity system with a 650 MDS
display/logger in sampling applications where the user is present?
Prior to observing or logging turbidity readings, you should always activate the wiper manually for the 650
keypad to remove bubbles/and or fouling.
What are the things most likely to give me problems when measuring turbidity with the 6136 probe
and YSI 6-series sondes?
The turbidity system has been designed to be easy to calibrate, easy to use in both sampling and
deployment applications, and trouble-free in normal usage. However, during our empirical testing, we
have observed occasional problems in calibration and in field applications. These difficulties are likely to
be experienced only infrequently by users. In fact, most of these problems are not due to any malfunction
in the turbidity system itself, but instead occur because of contaminated calibration solutions or the
presence of bubbles on the optics of the probe. However, we have gained experience in separating
problems which can be easily solved by the user from those which involve sensor malfunction and must be
dealt with by YSI Technical Support and Product Repair. This section is intended to pass this experience
along to the user.
You might see calibration errors. This problem could be due to bubbles on the optical surface,
contamination of your 0 NTU standard, or a higher calibration standard which has not been prepared
properly or has been contaminated or diluted inadvertently. The problem could also be due to an internal
malfunction of the probe optical system. To troubleshoot the problem, do not override the cal error, return
to the Main menu and activate Discrete Sampling in the Run mode. Remove the sonde guard and place
your thumb or finger over the optics of the probe while observing the data display. A high (>1000 NTU)
reading should be observed if the probe is responding correctly from an optical standpoint. If no response
is noted, the probe must be returned to YSI Product Service for repair or replacement. CAUTION: DO
NOT ATTEMPT TO DISASSEMBLE THE PROBE YOURSELF. If the probe is functioning properly,
replace the probe guard and place the sonde back into 0 NTU water. Activate the wiper manually and enter
the calibration routine of choice (1-, 2-, or 3-point) from the Calibrate menu. Observe the readings for the
0 NTU standard. If values higher than about 5 NTU are observed, it is possible that your 0 NTU standard
has been contaminated from debris that was retained on the sonde and probes from the previous field usage.
Discard the water, rinse the sonde, and replace in new 0 NTU standard. After agitation, check the reading
to see if it has been reduced. If so, proceed with the second calibration point. If not, contact YSI Technical
Support for further assistance. If a calibration error occurs on the second point, use a new source of
standard and try again. If an error still occurs, contact YSI Technical Support for further assistance.
You might observe slightly negative readings in very clear water. This effect is usually due to one of
two causes:
1.
The “zero” turbidity standard which you have used is not really 0 NTU because of inadvertent
contamination. This contamination usually occurs when the fouling from a sonde just taken from the
field contaminates the turbidity-free water used for the zero point. To overcome the problem, be sure
to clean the sonde as well as possible prior to recalibration of the turbidity sensor and then assure that
the zero reading is as low as possible by changing the turbidity-free water until no further lowering of
the reading is noted.