YSI 6000UPG - Manual (Page 103)

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deviation may also be due to fouling of the platinum ORP sensor. This problem can usually be
corrected by cleaning the platinum ring according to the manufacturer’s instructions.
To determine whether the sensor is functioning correctly, place the ORP probe in 3682 Zobell
solution and monitor the millivolt reading. If the probe is functioning within specifications, the
ORP reading should be within the range of 210-250 mv at normal ambient temperature. If the
reading is outside of this range, the probe should be cleaned, rechecked, and then can be calibrated
to the correct value (231 mV at 25
o
C) using the calibration procedure outlined in Section 4.2.
ORP readings for the same solution can vary up to 100 mv depending on the temperature.
However, no standard compensation algorithms exist for this parameter. Be sure to take this factor
into account when reporting ORP values and checking sensor calibration. For Zobell solution,
consult the following chart:
TEMPERATURE, CELSIUS ZOBELL SOLUTION VALUE, MV
-5 270
0 263.5
5 257
10 250.5
15 244
20 237.5
25 231
30 224.5
35 218
40 211.5
45 205
50 198.5
MEASUREMENT AND CALIBRATION PRECAUTIONS
(1) Instructions for preparation of ORP calibrator solutions can be found in Section 2580 A. of
Standard Methods for the Examination of Water and Wastewater. Alternatively, the reagent is
available from YSI.
(2) ORP readings usually stabilize much more rapidly in standards (e.g., Zobell solution) than in
most environmental water. Be certain to consider this factor when determining ORP in field
studies.
(3) Clean and store the pH/ORP sensor following the instructions in Section 7 and Appendix G of
this manual.