JUMO AQUIS touch P 202580, Operating Manual

Page: 175 / 322

175
13 Calibrating
a pH measuring chain
13.1 Notes
13.2 General information
The calibration of pH electrodes is based on measurements in Buffer solutions
with a defined pH-value. The pH values of the Buffer solutions used are speci-
fied either via entry of fixed values into the calibration default settings, entered
during the calibration or recognized automatically by "automatic buffer recogni-
tion" during the calibration process. For "automatic buffer recognition", a Buffer
set table must be selected in the calibration default settings. In this case, the
Buffer solutions used must be listed in the provided Buffer set table. Since pH
value measurement of liquids is temperature-dependent, the temperature of the
Buffer solution must be sensed in order to compensate for its effect on the result
of the measurement. This requires either manual entry or measurement with the
aid of a Temperature sensor.
13.2.1 Calibration methods for pH sensors
Zero-point calibration
This calibration method is used to determine the pH zero point on the measure-
ment characteristic curve. The Slope is retained.
A Buffer solution with a defined pH-value is needed as a reference.
Two-point Calibration
By measuring 2 different Buffer solutions with defined pH-values, the pH zero
point and pH slope of the measuring chain are established.
The pH-values of the Buffer solutions must be at least 2 pH apart. This calibra-
tion method is recommended for most applications.
Three-point calibration
With Three-point calibration, the pH zero point as well as the pH slope in the
acidic region and the pH slope in the alkaline region are established.
This method requires 3 Buffer solutions with defined pH-values as references.
One of these must be acidic, one neutral, and one alkaline. The pH values of the
Buffer solution must be at least 2 pH apart from one another. This calibration
method is recommended for applications with more demanding accuracy re-
quirements when performing measurements in both the alkaline and acidic re-
gions.
WARNING!
During the calibration, the relays and analog output signals assume the config-
ured states!