Knick Protos 3400, User Manual

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Calibration / Adjustment
Calibration Methods
One-Point Calibration
The electrode is calibrated with one buffer solution only.
Here, only the electrode zero point is detected and taken into account by the
Protos. One-point calibration is appropriate and permissible whenever the
measured values lie near the electrode zero point so that slope changes do not
have much of an impact.
Two-Point Calibration
The electrode is calibrated with two buffer solutions.
In that case, zero point and slope of the electrode can be detected and taken
into account by the Protos. Two-point calibration is required if
• the electrode has been replaced
• the measured pH values cover a wide range
• there is great difference between the measured pH value
and the electrode zero
• the pH measurement must be very accurate,
• the electrode is exposed to extreme wear.
Three-Point Calibration
The electrode is calibrated with three buffer solutions.
Zero and slope are calculated using a line of best fit according to DIN 19268.
Sensor Replacement (First Calibration)
A First Calibration must be performed each time the electrode is replaced.
During First Calibration, the electrode data together with the electrode type
and serial number are stored as reference values for electrode statistics.
The ”Statistics” menu of Diagnostics shows the deviations of zero, slope,
glass and reference electrode impedance, and response time of the last three
calibrations with respect to the reference values of the First Calibration.
This allows evaluation of the drift behavior and aging of the electrode.