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MODEL SOLU COMP II SECTION 6.0
CALIBRATION
6.7 ORP CALIBRATION
6.7.1 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.
6.7.2 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±20mVdc at 25°C. The redox poten-
tial is -476±20mVdc at 25°C.
6.7.3 Procedure
CCaalliibbrraattee
Hold
Program Display
Calibrate?
SSeennssoorr11
Sensor2
CalSensor1?
MMeeaassuurreemmeenntt
Temp
Live 600mV
CalS1
++
0000mV
1. Press MENU. The main menu screen appears. Choose Calibrate.
2. Choose Sensor1 (ORP sensor).
3. Choose Measurement.
4. The top line shows the actual ORP or redox potential (S1Live). Once the
reading is stable, change the number in the second line to the desired
value. Press ENTER.
5. The display returns to the screen in step 2. Choosing Sensor2 will per-
mit the conductivity measurement to be calibrated.
6. To return to the main display, press MENU followed by EXIT.