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MODEL 399VP pH/ORP SENSOR SECTION 4.0
START-UP AND CALIBRATION
SECTION 4.0.
START-UP AND CALIBRATION
4.1 SENSOR PREPARATION
Shake down the sensor to remove any air bubbles that may be present in the tip of the pH glass bulb. In most
cases, the pH sensor can simply be installed as shipped, and readings with an accuracy of ± 0.6 pH may be
obtained. To obtain greater accuracy or to verify proper operation, the sensor must be calibrated together with its
compatible analyzer or transmitter.
4.2 pH CALIBRATION
After a temporary connection is established between the sensor and the instrument, a buffer calibration may be
performed. Consult the appropriate pH/ORP analyzer or transmitter instruction manual for specific calibration and
standardization procedures, or see below for recommended two-point buffer calibration procedure.
Recommended two-point buffer calibration procedure:
Select two stable buffer solutions, preferably pH 4.0 and 10.0 (pH buffers other than pH 4.0 and pH 10.0 can be
used as long as the pH values are at least two pH units apart).
NOTE
A pH 7.0 buffer solution reads a mV value of approximately zero, and pH buffers read approximately
59.1 mV for each pH unit above or below pH 7.0. Check the pH buffer manufacturer specifications for mil-
livolt values at various temperatures, since it may affect the actual value of the buffer solution mV/pH
value.
1. Immerse the sensor in the first buffer solution. Allow the sensor to adjust to the buffer temperature (to avoid
errors due to temperature differences between the buffer solution and sensor temperature) and wait for the
reading to stabilize. The value of the buffer can now be acknowledged by the analyzer/transmitter.
2. Once the first buffer has been acknowledged by the analyzer/transmitter, rinse the buffer solution off of the
sensor with distilled or deionized water and/or a small quantitiy of the next buffer solution.
3. Repeat steps 1 and 2 using the second buffer solution.
4. Once the analyzer/transmitter has acknowledged both buffer solutions, a sensor slope (mV/pH) is established
(the slope value can be found within the analyzer/transmitter).
5. The slope value should read about 59.1 mV/pH for a new sensor and will decrease over time to approximate-
ly 47-49 mV/pH. Once the slope reads below the 47-49 mV/pH range, either clean the sensor and recalibrate
for a better slope or install a new sensor to maintain accurate readings.
Recommended pH Sensor S
tandardization:
For maximum accuracy, the sensor can be standardized online or with a process grab sample after a buffer cali-
bration 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.
1. While obtaining a process solution sample (it is recommended that the sample be taken close to the sensor),
record the pH value that is shown on the analyzer/transmitter display.
2. Measure and record the pH of the process solution sample with another temperature compensated, calibrat-
ed pH instrument. For best results, standardization should be performed at the process temperature.
3. Adjust the analyzer/transmitter value to the standardized value.
4.1 SENSOR PREPARATION
4.2 pH CALIBRATION
4.3 ORP CALIBRATION