Specifications

44
MODEL 30 pH/DO SECTION 6.0
CALIBRATION
6.8 ORP CALIBRATION
6.8.1 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.
6.8.2 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.
6.8.3 Procedure
CCaalliibbrraattee
Hold
Program Display
Calibrate?
Sensor1
SSeennssoorr22
CalSensor2?
MMeeaassuurreemmeenntt
Temp
Live 600mV
CalS2
++
0000mV
1. Press MENU. The main menu screen appears. Choose Calibrate.
2. Choose Sensor2 (ORP sensor).
3. Choose Measurement.
4. The top line shows the actual ORP or redox potential (S2Live). 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 Sensor1 will per-
mit the dissolved oxygen measurement to be calibrated.
6. To return to the main display, press MENU followed by EXIT.