YSI 550A - Manual (Page 12)

Page 8
Y S I
Environmental
YSI 550A
PROBE OPERATION
NOTE: The YSI 550A DO Instrument should not be used in a purpose other than that specified by
YSI Incorporated. See Warranty for details.
STIRRING
It is important to recognize that a very small amount of oxygen dissolved in the sample is consumed
during probe operation. It is therefore essential that the sample be continuously stirred at the sensor tip.
If stagnation occurs, measurements will appear artificially low.
Stirring may be accomplished by mechanically moving the sample around the probe tip, or by moving
the probe through the sample. The YSI Model 550A has a flow dependence of <25%. The rate of
stirring required is 1/2 foot per second (16cm per second).
MEASUREMENT PROCEDURE
1.
Insert the probe into the sample to be measured.
2. Continuously stir or move the probe through the sample.
3. Allow temperature and dissolved oxygen readings to stabilize.
4. Observe/Record readings.
5. If possible, rinse the probe with clean water after each use.
PRECAUTIONS
1. Membranes last longer if properly installed and regularly maintained. Erratic readings can result
from loose, wrinkled, damaged, or fouled membranes, large (more than 1/8" diameter) air bubbles
in the electrolyte reservoir, or membrane coating by oxygen consuming (e.g. bacteria) or oxygen
producing (e.g. algae) organisms. If unstable readings or membrane damage occurs, replace both
the membrane cap and electrolyte solution.
2. Chlorine, sulfur dioxide, nitric oxide, and nitrous oxide can affect readings by behaving like oxygen
at the probe.
3. Avoid substances such as acids, caustics, and strong solvents, which may damage probe materials.
Probe materials include the PE membrane, acrylic plastic, EPR rubber, stainless steel, epoxy,
polyetherimide and the PVC cable covering.
4. Always store the probe in the calibration/storage chamber with the moistened sponge.