Selecting the calibration process
Select the calibration process prior to ini‐
tial calibration. This selection is saved
until you select a new process.
n 2-point calibration: This is the recom‐
mended calibration process because
it evaluates the sensor characteristic
data: asymmetric potential, slope and
response speed. 2 buffer solutions
are needed for 2-point calibration, e.g.
pH 7 and pH 4 if subsequent meas‐
urement is to be performed in an
acidic medium or pH 7 and pH 10, if
subsequent measurement is to be
performed in an alkaline medium. The
buffer gap should be at least 2 pH
units.
n Samples (1-point) calibration: There
are two options here. Samples (1-
point) calibration is only recom‐
mended with reservations. From time
to time check the sensor with 2-point
calibration.
– The pH sensor remains in the
sample medium and you should
calibrate a sample of the medium
to be measured against an
external comparison measure‐
ment. Perform the comparison
measurement using an electro‐
chemical method. Deviations of
up to ± 0.5 pH units can occur
using the phenol red method
(photometer).
– Calibration solely using a pH 7
buffer. This only calibrates the
zero point. The sensor is not
checked for an acceptable slope.
n Data input: With this calibration
method, using a comparison meas‐
uring device, determine in advance
the characteristic data of the pH
sensor (asymmetry and slope) at
standard temperature and enter this
data into the controller. The compara‐
tive calibration should not be more
than one week old because the pH
sensor's characteristic data changes if
the data is saved for longer.
Calibration
63
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