Calibration - pH and ORP
Instruction Manual
February 2014
LIQ_MAN_6081-P
30
Calibration - pH and ORP
and offset. The slope is reported as the slope at 25 °C. Figure 10-1 defines the terms. The trans
-
mitter can also be standardized. Standardization is the process of forcing the transmitter reading
to match the reading from a second pH instrument. Standardization is sometimes called a one-
point calibration.
Figure 10-1. Calibration Slope and Offset
10.2
Procedure - Auto Buffer Calibration
1. Obtain two buffer solutions. Ideally, the buffer values should bracket the range of pH values to
be measured.
2. Remove the pH sensor from the process liquid. If the process and buffer temperatures are
appreciably different, place the sensor in a container of tap water at the buffer temperature. Do
not start the calibration until the sensor has reached the buffer temperature. Thirty minutes is
usually adequate.
3. Press MENU. The main menu appears. Choose Calibrate.
4. Choose pH.
5. Choose BufferCal.
6. Choose Auto.
7. To continue with the calibration, choose Buffer1.Then go to step 8. To change stability criteria,
choose Setup and go to step 19.
8. Rinse the sensor with water and place it in buffer 1. Be sure the glass bulb and the reference
junction are completely submerged. Swirl the sensor.
9. The screen at left is displayed with “Wait” flashing until the reading is stable. The default
stability setting is <0.02 pH change in 10 sec. To change the stability criteria, go to step 19.
When the reading is stable, the screen in step 10 appears.
10. The top line shows the actual reading. The transmitter also identifies the buffer and displays
the nominal buffer value (buffer pH at 25 °C). If the displayed value is not correct, press or to
display the correct value. The nominal value will change, for example from 7.01 to 6.86 pH.
Press ENTER to store.
11. The screen at left appears momentarily.
12. The screen at left appears. Remove the sensor from Buffer 1, rinse it with water, and place it in
Buffer 2. Be sure the glass bulb and the reference junction are completely submerged. Swirl
the sensor. Choose Buffer2.
13. The screen at left is displayed with “Wait” flashing until the reading is stable. When the
reading is stable, the screen in step 14 appears.
14. The top line shows the actual reading. The transmitter also identifies the buffer and displays
the nominal buffer value (buffer pH at 25°C). If the displayed value is not correct, press or to
display the correct value. The nominal value will change, for example from 9.91 to 10.02 pH.
Press ENTER to store.
15. The screen at the left appears momentarily.
16. If the calibration was successful, the transmitter will display the offset and slope (at 25°). The
transmitter can also be standardized.
Standardization is the process of
forcing the transmitter reading to
match the reading from a second
pH instrument. Standardization
is sometimes called a one-point
calibration.
