ProMinent DULCOMETER diaLog DACb Assembly And Operating Instruction page 83

Selecting the calibration process
Select the calibration process prior to initial cali‐
bration. This selection is saved until you select
a new process.
2-point calibration: This is the recom‐
n
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 sub‐
sequent measurement is to be performed
in an acidic medium or pH 7 and pH 10, if
subsequent measurement is to be per‐
formed in an alkaline medium. The buffer
gap should be at least 2 pH units.
Samples (1-point) calibration: There are
n
two options here. Samples (1-point) cali‐
bration is only recommended with reserva‐
tions. 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 meas‐
ured against an external comparison
measurement. Perform the compar‐
ison 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.
Data input: With this calibration method,
n
using a comparison measuring 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 have been done
more than a week before, as the pH sen‐
sor's characteristic data changes if it is
stored for longer.
Buffer temperature dependencies
Buffer temperature
At temperatures that differ by 25°C in
the process, adjust the pH of the buffer
solution by entering the reference
values printed on the buffer solution
bottle into the controller prior to calibra‐
tion.
Buffer temperature dependencies
An incorrectly entered buffer tempera‐
ture can lead to incorrect calibration.
Each buffer has different temperature
dependencies. You have various
choices in terms of compensating for
these temperature dependencies, so
that the controller can correctly process
the buffer temperature.
Buffer temperature [Manual]:
–
Ensure that the buffer temperature
is identical for both buffers. Enter
the buffer temperature in the
[CAL Setup] menu item in the con‐
troller.
Buffer temperature [Automatic]:
–
Then immerse the temperature
sensor connected to the controller
together with the pH sensor into
the buffer. Wait for a sufficiently
long period of time until the pH
and temperature sensor have
recorded the buffer temperature.
Buffer temperature [Off]: this set‐
–
ting is not recommended. Please
use another setting.
Calibration
83