YSI 6500 Environmental Process Monitor - Manual (Page 52)

Proper Use and Care of the 6500
Section 5
The sensors associated with the 6-Series Sonde are of high quality and should exhibit excellent
performance in your application in excess of the warranty period. However, the dissolved
oxygen, pH, and conductivity sensors will inevitably show some drift during deployment due to
natural chemical changes to the reagents in the probes, physical changes of the electrodes, minor
fouling of the sensor surfaces, or all of these factors. Noisy sensor readings (especially for the
conductivity and dissolved oxygen sensors) signal the need for specific maintenance procedures.
With these factors in mind, it will be imperative for you to establish and carry out regular checks
of the quality of your sensor readings in order to assure that they are performing within their
specifications, particularly if you are using the readings in compliance reporting.
We recommend that you carry out the following quality assurance program WEEKLY during the
initial use of your 6500 system. After several weeks of this program, you should be able to
ascertain if this frequency is appropriate for your application. If only minimal drift is observed,
then the frequency of implementing the protocol can be decreased. The procedure is relatively
simple and should take only about 20 minutes to complete.
Normally, the quality assurance measurements and recalibration can be carried out at the
deployment site using the 6500 Monitor to assess the drift and to recalibrate if necessary. This
method may not require the removal of the sonde from the water, greatly facilitating
redeployment and shortening the downtime of the instrument. However, there are some
circumstances in which the sonde should be removed to the laboratory and interfaced with a PC
or 610 data logger for quality assurance procedures. For example, the pH sensor should never be
exposed for more than a few minutes to subfreezing air temperatures, so under these conditions,
an evaluation of the sensors in the field would likely cause damage to a key sensor and should be
done in the laboratory instead.
5.2.3 RECOMMENDED QUALITY ASSURANCE PROTOCOL
1. Take the following items to the deployment site:
-bucket of clean water
-the small brush supplied with the 6-Series Sonde
-the calibration/storage vessel supplied with the 6-Series Sonde
-pH 7 buffer and another pH buffer (usually pH 4 or pH 10) of your choice
-latex gloves
2. Before going to the site, determine the current local barometric pressure reading.
3. Remove the sonde from the stream and the sonde guard from the probe compartment.
4. Manually remove any gross debris from the sensors and then rinse carefully in a bucket of
clean water, being very careful not to damage the sensors.
5. Using the small brush provided with the sonde, repeatedly scrub the two conductivity
channels. After brushing is complete, rinse the sensor with clean water by immersion in or
spraying with clean water.
6. While the sonde guard is removed, inspect the dissolved oxygen membrane for obvious holes
or tears and the silver anodes for excessive darkening. Do not remove the membrane at this
time.
YSI Incorporated 6500 Environmental Process Monitor 49