Table of Contents
Advertisement
Instruction Manual
LIQ-MAN-PERpH-X
Section 3: Startup and Calibration
3.1
Electrode Preparation
1.
2.
3.
CAUTION
The buffer in the protective boot may cause skin or eye irritation.
3.2
pH Sensor Calibration
3.2.1
Two Point pH Buffer Calibration
Select two stable buffer solutions, preferably pH 4.0 and 7.0 (pH buffers other than pH 4.0 and
pH 7.0 can be used as long as the pH values are at least two pH units apart).
Note:
1.
2.
3.
4.
3.3
Recommended pH Sensor Standardization
For maximum accuracy, the sensor can be standardized on-line or with a process grab sample after
a buffer calibration has been performed and the sensor has been conditioned to the process.
Standardization accounts for the sensor junction potential and other interferences.
Standardization will not change the sensor's slope but will simply adjust the analyzer's reading to
match that of the known process pH.
Startup and Calibration
Remove electrode from shipping container.
Remove the protective boot covering the electrode bulb.
Rinse away salt film with clean water, then gently shake the electrode so that the internal
solution fills the bulb, thus removing any air trapped there.
A pH 7 buffer solution reads a mV value of approx. zero, and pH buffers read
approximately ± 59.1 mV for each pH unit above or below pH 7. Check the pH buffer
manufacturer specifications for millivolt values at various temperatures since it may affect
the actual value of the buffer solution mV/pH value.
Immerse the sensor in buffer solution. The buffer solution must contact the metal housing
of the sensor which acts as the solution ground contact. Allow sensor to equilibrate to the
buffer temperature and wait for reading to stabilize. Value of buffer can now be
acknowledged by the transmitter.
Once the first buffer has been acknowledged by the transmitter, rinse the buffer solution
off of the sensor with distilled or deionized water.
Repeat steps 1 and 2 using the second buffer solution.
The theoretical slope value, according to the Nernst equation for calculating pH, is
approximately 59.17 mV/pH. Over time the sensor will age, both in the process and in
storage, and will result in reduced slope values. To ensure accurate readings, it is
recommended that the electrode be replaced when the slope value falls below
47 to 49 mV/pH.
Startup and Calibration
April 2017
21
Hide quick links:
Advertisement
Table of Contents
