YSI 6 series User Manual page 354

ROX Optical DO Sensor
•
When prompted for the input of a barometer or a concentration value, type the word "uncal" and
press Enter if your sonde is attached to a computer. If your sonde is attached to a 650 MDS,
when prompted for input, hold down the Enter key and press the Esc key.
Either procedure will reset your 6150 calibration constants to the previously input values associated with
your sensor membrane.
How often should I calibrate my ROX sensor?
Our experience is that, even though the drift of the ROX sensor is minimal, it is prudent to calibrate the
sensor in air-saturated water or water-saturated air prior to each deployment or field sampling study. The
calibration takes very little time and should be carried out to (a) maintain the best possible accuracy for the
sensor and (b) to assure that the sensor is working properly prior to proceeding to the field.
I notice that, during Discrete Sample studies, there is a lag between when I begin the sampling and
when ROX DO readings actually appear on the display. What is causing this effect?
The lag between starting the study and actually seeing data is due to the fact that the readings of all optical
sensors, including ROX DO, are frozen during the sensor wiping sequence. If the sonde has not been used
for more than a minute, it will be in the "sleep" mode and, under these conditions, all optical sensors will
automatically wipe the first time a Discrete Sample command is issued. The extent of the lag varies
depending on how many optical sensors are present in the sonde and will be about 15 seconds per optical
sensor. Thus, lag will be about 15 seconds for a sonde with two optical sensors and about 1 minute for a
sonde with four optical sensors.
How does the ROX sensor deal with fouling in field studies?
The ROX sensor has a wiper similar to those used on all YSI optical sensors (turbidity, chlorophyll,
rhodamine WT, and blue-green algae) which removes fouling from the sensor membrane. The wiper
activates just prior to each measurement point in a long term study. In addition, the wiper can be activated
manually from a PC keyboard or from a 650 MDS handheld logger to remove bubbles from the sensor
membrane prior to spot sampling measurements.
What color wiper should be used with the ROX DO sensor?
Because the probe is digital, you can use any color wipers with the 6150 ROX sensor. In fact, if you are
using the ROX sensor in the "T" port of a 6600EDS V2-2 sonde, you should use the white EDS wiper for
the application. However, just to be consistent, YSI recommends that you use black wipers for the ROX
sensor like those supplied with the probe for all 7non-EDS applications. The wiper is a wear item and a
spare is provided with each probe along with a 0.05" hex key to loosen/tighten the wiper set screw. Black
wiper packs, YSI 6625, can be ordered from YSI Technical Support or Customer Service. Alternatively,
users who choose to change only the wiper pad can purchase the YSI 6144 Optical Wiper Pad Kit.
What is the response time of the ROX DO sensor?
On transfer to field water, typically the ROX sensor will reach 90% of its final value in less than 30
seconds – slightly faster than the YSI Rapid Pulse sensor. Note, however, that the response time of the
ROX probes varies slightly from sensor module to sensor module.
YSI Incorporated Environmental Monitoring Systems Operations Manual
Appendix M
M-
5