2 orp calibration, Calibration, Mv δ – Hach-Lange SI792 P, SI792x P, SI792x P-FF, SI792x P-PA User Manual User Manual
Page 77
Calibration
75
8.1.2
ORP calibration
The ORP probe is calibrated using an ORP (redox) standard solution.
The probe can also be calibrated by product comparison
(
).
During calibration, the difference between the measured potential and
the specified potential of the calibration standard is determined. In the
measurement mode, this difference is added to the measured potential
to obtain the displayed potential (equation
(1)
).
(1)
where:
mV
ORP
= displayed ORP
mV
meas
= direct probe potential
ΔmV = delta value, determined during calibration
The probe potential can also be related to another reference system
such as the standard hydrogen probe. In this case the temperature-
corrected potential (
Table 20
) of the reference probe used must be
entered during calibration. During measurement, this value is then
added to the measured potential.
Table 20 Temperature-corrected potential of
commonly used reference systems
Temperature
(°C)
Ag/AgCl/KCl
1 mol/L
(
Δ
mV)
Ag/AgCl/KCl
3 mol/L
(
Δ
mV)
Thalamid
(
Δ
mV)
Mercuric
sulfate
(
Δ
mV)
0
249
224
–559
672
10
244
217
–564
664
20
240
211
–569
655
25
236
207
–571
651
30
233
203
–574
647
40
227
196
–580
639
50
221
188
–585
631
60
214
180
–592
623
mV
ORP
mV
meas
mV
Δ
+
=