YSI 58 - Manual (Page 18)

NOTE: If calibration is performed in the percent air saturation mode, the operator need not calculate
for temperature; but will simply set the display to read CALIB VALUE for the pressure/altitude table
according to the local altitude or the true barometric pressure at the point of measurement.
4.3.4 CALIBRATION FREQUENCY
Daily calibration is generally appropriate. Calibration can be disturbed by physical shock, touching
the membrane, fouling of the membrane or drying out of the electrolyte. Check calibration after each
series of measurements, and in time you will develop a realistic schedule for recalibration. When
probes are not in use, store them according to the procedures in Section 5, Care and Maintenance.
4.4 MAKING MEASUREMENTS
For accurate measurement, water movement of one foot per second or more is required so that the
oxygen –depleted layer of the sample at the membrane surface is flushed away and replenished. A
moving stream can provide this motion; alternatively, the probe can be moved through the sample by
hand. The YSI 5795A Submersible Stirrer supplies the necessary stirring for the 5739 probe. The YSI
5905 BOD probe has its own line powered stirrer for laboratory use. When the 5750 BOD probe is
used, stirring must be provided such as with a magnetic stirrer.
1.
With the instrument prepared for use, and the probe calibrated, place the probe in the sample.
If the 5795A stirrer is to be used, connect it and turn the STIRRER switch to ON. Connect
the recorder, if it is used.
2.
Adjust the SALINITY control to the salinity of the sample. (Not required when reading %
air saturation).
3.
Turn the function switch to 02 ZERO and readjust if necessary.
4.
Turn the function switch to the desired readout mode and read the dissolved oxygen value in
mg/L or in % air saturation when the meter reading has stabilized.
4.4.1 ENVIRONMENTAL CONSIDERATIONS
¾ Erroneous readings will be made in any environment where the probe’s Teflon membrane will
become rapidly coated with oxygen consuming or oxygen evolving organisms. In some cases, the
YSI 5795A Submersible Stirrer can provide adequate cleaning action due to its high turbulence.
¾ Erroneous readings will be made in any environment where heavy residue may coat the probe’s
membrane. In such instances, problems generally can be eliminated by more frequent probe
service and/or cleaning.
¾ Erroneous readings will be made in any environment where dissolved gases are present that will
chemically interfere with the probe’s electrochemistry. Known interfering gases are hydrogen
sulfide, sulfur dioxide, halogens, neon, nitrous oxide and nitric oxide.
¾ Also avoid any environment that contains substances that may attack the probe materials. Some
of these substances are concentrated acids, caustics and strong solvents. The probe materials that
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