Cotter Corporation (N.S.L.)
Cañon City Milling Facility
Cañon City, Colorado
Procedure
Oxidation Reduction
Potential Measurements
Number: E-046
Page 4 of 6
Revision: 1
Date: --/--/--
10.4
If the mV meter will not calibrate refer to the specific meter/instrument operating
instruction manual for troubleshooting and maintenance information or replace
the meter or probe with a spare meter or mV probe.
11.0
MEASUREMENT INSTRUCTIONS
Direct measurements for ORP are made by simply taking a measurement of a sample,
correcting to units of Standard Hydrogen Electrode (SHE) and reporting a result.
11.1
Direct Measurement Of Samples.
11.1.1
Insert a proper functioning electrode into the water sample to be measured.
11.1.2
Take a reading in mV by following the directions in the pH/mV meter
operator's manual.
11.1.3
When the reading stabilizes, record the sample temperature and mV value
as displayed on the meter.
11.1.4
It is necessary to report the value relative to the results achieved by a
"normal standard hydrogen electrode" as the reference electrode. To do
this you must add the observed mV result to the potential of the reference
electrode being used - in this case a 4 M KCL with Ag/Ag CI electrode,
which has a value of 200 mV at 25
o
C. This is necessary since the value of
the "normal standard hydrogen electrode” is defined as having a value of
0.0 mV under the same conditions.
11.1.5
Refer to appendix 5.1 for the offset correction factor to use for
measurements at temperatures different than 25
o
C
Where
Eh = the value of the potential of the sample relative to the “normal
standard hydrogen electrode”
Eo = the potential observed with the ORP electrode (the result from the
meter)
11.1.6
C
f
= Correction Addition Factor is the constant offset factor in potential
due to the reference electrode in use (in this example 200 mV for a
temperature of 25
o
C).
11.1.7
If your meter reported a value of 450 mV at a temperature of 25
o
C, your
reported result would be Eh = 450 + 200, or 650 mV (SHE). If the value
reported was -599 at a temperature of 25
o
C your reported result would be
Eh = -599 + 200, or -399 mV (SHE).
Содержание sympHony
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