wtw NitraLyt 700 IQ, Operating Manual, Page: 23 / 61

NitraLyt
®
700 IQ Calibration and measuring
4 - 3 ba75397d03 12/2004
4.1.3 Calibrating in practice
Initial calibration The first calibration (initial calibration) is especially important as it is the
reference point for all other calibrations (following calibrations).
An initial calibration is required each time an electrode is commis-
sioned. The initial calibration is switched on and off in the setting menu
of the sensor (see section 3.4).
With the initial calibration, the zero point for the drift potential is deter-
mined. It serves as the reference value for the drift potential, which is
determined and recorded in the calibration log with every following cal-
ibration. In addition to the slope, the drift potential informs about the
age condition of the electrode (see section 4.1.10).
Note
An optimum initial calibration is achieved by a calibration procedure
that determines the current slope of the electrode (
2 point stand. (3) or
Double std. add. (5) ). If the slope is not determined, the default setting
(-59.16 mV) is taken over. A value that is taken over is marked with * in
the calibration history (see section 4.1.10).
Following the initial calibration, we recommend to carry out a calibration
with the
1 point ref. (2) procedure in order to compensate for matrix
effects of the real test sample. Apart from that, the chloride content of
the test sample should be determined and checked for whether a chlo-
ride compensation is required (see section 4.2.1).
Following calibrations Basically, any calibration procedure can be used for the following cali-
brations. The slope of the electrode should be determined at regular
intervals in any case in order to be able to evaluate the aging of the
electrode. If the electrode cannot be calibrated any more because the
slope is too low it is blocked for measurement and has to be
exchanged.
"Emergency operation"
with invalid slope
After determining an invalid slope, the sensor can be further operated
with a subsequent valid single-point calibration as a stopgap solution
until the electrode is exchanged. The last valid slope is used in the
measuring operation. With the single-point calibration, a corresponding
note appears quoting the slope that is used.