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Sondes Section 2
YSI Incorporated Environmental Monitoring Systems Operations Manual 2-81
NOTE CAREFULLY: If you used sodium sulfite solution as your zero calibration medium, you
MUST carefully remove all traces of the reagent from the probes prior to proceeding to the second
point. YSI recommends that the second calibration point be in air-saturated water if you use
sodium sulfite solution as your zero oxygen medium.
After confirming the zero point calibration, place the sensors in the medium containing a known oxygen
pressure or concentration and wait at least 10 minutes for temperature equilibration. Then enter either the
barometer reading in mm Hg (for
ODO% 2-Point
calibrations) or the actual concentration of oxygen
which was probably determined from a Winkler titration (for
ODO mg/L 2-Point
calibrations). Press
Enter and observe the readings in real time until they are stable. Then press Enter again to confirm the
calibration. The screen will indicate that the calibration has been accepted and prompt you to press Enter
again to return to the Calibrate menu.
CAUTION: Carrying out DO mg/L calibrations at values outside the range of +/- 10 % of air
saturation for the second calibration point in the 2-Point routine is likely to compromise the quoted
accuracy specification of the 6150 Optical DO Sensor.
NOTE CAREFULLY: It will normally not be necessary to perform 2-Point calibrations for the 6150
Optical DO Sensor and the procedure is not recommended unless (a) you are certain that the sensor
does not meet your accuracy requirements at low DO levels and (b) you are operating under
conditions where you are certain to be able to generate a medium which is truly oxygen free.
Note that the parameter “ODOsat %Local” is also available for users who prefer to set their percent air
saturation value to 100%, no matter what barometer value is entered. The method of activating this
parameter, its use, and its limitations are described in Appendix J of this manual. The key factor to
remember, however, is that no matter which convention (ODOsat % or ODOsat %Local) is selected, the
mg/L value will not be affected.
PRESSURE – ABS AND GAGE
Select
Pressure – Abs (non-vented) or Gage (vented)
to zero the depth sensor. The depth sensor is
factory calibrated, but it is always necessary to zero the absolute sensor relative to the local barometric
pressure. A minor correction is also sometimes necessary to set the Gage (vented) sensor output to exactly
0.000 feet or meters. The zeroing procedure should be carried out with the sonde in air for this initial
calibration. Alternatively, you may set zero or an offset while the sonde is submersed for “relative depth”
applications. After the depth option is selected, enter 0.00 (or other appropriate value in feet or meters
depending on your Report setup) at the prompt, press Enter and monitor the stabilization of the depth
readings. After no changes occur for approximately 30 seconds, press Enter to confirm the calibration. As
instructed, press
Enter
again to return to the Calibrate menu.
Zeroing the depth sensor by the above protocol (entering 0.00 at the screen prompt) will result in a
measurement of the distance between the water surface and the ports of the depth module. In order for the
observed depth readings to reflect the distance between the water surface and the actual probe array,
measure the length between the upper hole and the bottom of the sonde guard. Then, if you are concerned
about this small difference, enter the measured difference (in feet or meters depending on your Report
setup) at the screen prompt instead of 0.00.
For best performance of depth measurements, users should ensure that the sond
e‟
s orientation remains
constant while taking readings. This is especially important for vented level measurements and for sondes
with side mounted pressure sensors.