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MODEL 6081-P pH/ORP SECTION 10.0
CALIBRATION – PH
10.6 ORP CALIBRATION
10.6.1 Purpose
1. For process control, it is often important to make the measured ORP agree with the ORP of a standard solu-
tion.
2. During calibration, the measured ORP is made equal to the ORP of a standard solution at a single point.
10.6.2 Preparation of ORP standard solutions
ASTM D1498-93 gives procedures for the preparation of iron (II) - iron (III) and quinhydrone ORP standards. The
iron (II) - iron (III) standard is recommended. It is fairly easy to make, is not particularly hazardous, and has a shelf
life of about one year. In contrast, quinhydrone standards contain toxic quinhydrone and have only an eight-hour
shelf life.
Iron (II) - iron (III) standard is available from Rosemount Analytical as PN R508-16OZ. The ORP of the standard
solution measured against a silver-silver chloride reference electrode is 476±20mV at 25°C. The redox potential is
-476±20mV at 25°C.
10.6.3 Procedure
1. Press MENU. The main menu screen appears. Choose Calibrate.
2. Choose ORP.
3. The top line shows the actual ORP or redox potential (Live). Once the reading is stable, change the number
in the second line to the desired value. Press ENTER.
4. The screen on the left will appear briefly.
5. The display returns to the Cal Sensor screen. Press EXIT. Choose the other sensor and repeat steps 2 through 4.