7.1.5 Standardization for pH
Standardization overview
Standardization is used to match the transmitter values with that of another transmitter.
The difference between the two pH values is converted into an equivalent voltage, called
the reference offset.
Note
If a sensor that has been calibrated with buffers is standardized, then placing it back in the buffer will
show a different measured pH than that of the buffer due to the standardization offset.
Standardization procedure
1. Enter the CALIBRATE menu by pressing CAL on the IRC.
The CALIBRATE submenu appears.
2. At the CALIBRATE submenu, press NEXT.
The STD submenu appears.
3. Press ENTER to enter the STD prompt.
The process pH and temperature should be relatively stable.
4. Take a grab sample from the process stream as close to the pH sensor as possible.
This transmitter reading is called the pH_trans.
5. Measure the pH of the sample (pH_std) using the second pH meter.
6. Note the current process reading (pH_curr). Calculate the corrected reading from
the equation: ph_corr = ph_curr + (pH_std - pH_trans)
• pH_corr = corrected pH value
• pH_curr = current pH value
• pH_std = standard instrument's pH value
• pH_trans = measured sample's pH value
7. Use the editing keys to enter the pH_corr value calculated using the equation above.
Press ENTER to save the value.
If the corrected value is acceptable, then the display shows the slope (current
electrode slope).
8. If the slope is acceptable, press EXIT. If the slope is unacceptable, use the editing
keys to change it. Then press ENTER.
9. To leave the CALIBRATE menu, press EXIT.
Measurements
44 Rosemount 5081
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