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5.1 START UP. To obtain best accuracy, the sensor
must be calibrated as a loop with the analyzer. Please
refer to the respective analyzer/transmitter instruction
manual for proper calibration procedures.
5.2 396R pH CALIBRATION
1. After a temporary connection is established
between the sensor and the instrument, a buffer
calibration may be performed.
2. 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.
5.2.1 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 buffer solution reads a mV value
of approx. zero, and pH buffers read approx.
+/- 59.1 mV for each pH unit above or below
pH 7. Check the pH buffer manufacturer spec-
ifications for millivolt values at various temper-
atures 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 solution 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.
5.2.2 Recommended pH Sensor Standardization
For maximum accuracy, the sensor can be standard-
ized 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 sen-
sor’s slope but will simply adjust the analyzers 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.
2. Measure and record the pH of the process solution
sample with a another temperature compensated,
calibrated pH instrument. For best results,
standardization should be performed at the
process temperature.
3. Adjust the analyzer/transmitter value to the
standardized value.
MODEL 396R pH/ORP SECTION 5.0
START UP AND CALIBRATION
SECTION 5.0
START UP AND CALIBRATION