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Section 4: Start-Up and Calibration
4.1 396P and 396PVP pH Sensors
4.1.1 Sensor preparation
Shake down the sensor to remove any air bubbles that may be present at the tip of the pH glass
bulb. In most cases, the pH sensor can simply be installed as shipped and readings with an accu-
racy of ± 0.6 pH may be obtained. To obtain greater accuracy or to verify proper operation, the
sensor must be calibrated as a loop with its compatible analyzer or transmitter.
4.1.2 pH Calibration
After a temporary connection is established between the sensor and the instrument, a buffer
calibration may be performed. Consult 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 manufac-
turer specifications for millivolt values at various temperatures since it may affect the actual value
of the buffer solution mV/pH value.
1. Immerse sensor in the first buffer solution. Allow sensor to adjust to the buffer temperature
(to avoid errors due to temperature differences between the buffer solution and sensor
temperature) and wait for reading to stabilize. Value of buffer can now be acknowledged by
analyzer/transmitter.
2. Once the first buffer has been acknowledged by the analyzer/transmitter, rinse the buffer solu-
tion off of the sensor with distilled or deionized water.
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
approximately 47-49 mV/pH. Once the slope reads below the 47-49 mV/pH range, a new
sensor should be installed to maintain accurate readings.
Recommended pH Sensor Standardization:
For maximum accuracy, the sensor can be standardized online 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.
1. While obtaining a process solution sample (it is recommended that the sample is taken close
to the sensor), record the pH value that is shown on the analyzer/transmitter display.
Start-Up and Calibration 35
396P + 396PVP Sensors Instruction Manual Section 4: Start-Up & Calibration
LIQ_MAN_396P_396PVP August 2013