Hach-Lange SI794 P User Manual - Manual (Page 78)

78
ORP calibration
ORP calibration mode is automatically preset when ORP measurement is
configured. The potential of a redox electrode is calibrated using a redox
(ORP) buffer solution. In the course of that, the difference between the
measured potential and the potential of the calibration solution is deter-
mined according to the following equation. During measurement this
difference is added to the measured potential.
0
10
20
25
30
40
50
60
70
80
Temperature
[°C]
Ag/AgCl/KCl
1 mol/L
[∆mV]
Ag/AgCl/KCl
3 mol/L
[∆mV]
Thalamid
[∆mV]
Mercury
sulfate
[∆mV]
249
244
240
236
233
227
221
214
207
200
224
217
211
207
203
196
188
180
172
163
-559
-564
-569
-571
-574
-580
-585
-592
-598
-605
672
664
655
651
647
639
631
623
613
603
Temperature dependence of commonly used reference
systems
The electrode potential can also be related to another reference system –
e.g. the standard hydrogen electrode. In that case the temperature-
corrected potential (see table) of the reference electrode used must be
entered during calibration. During measurement, this value is then added
to the ORP measured.
Please make sure that measurement and calibration temperature are the
same, since the temperature response of the reference electrode is not
automatically taken into account.
mVORP = mVmeas + ∆mV
mV
ORP
=
mV
meas
=
∆mV =
displayed ORP
direct electrode potential
delta value, determined during
calibration