Metrohm 840 PC Control 5.0 / Touch Control - Manual (Page 269)

4 Parameters
PC Control / Touch Control
257
4.7 Calibrating pH electrodes (CAL pH) and ISE
(CAL Conc)
For pH measurements, titrations to a preset endpoint (SET pH) and
the determination of pK values and fixed endpoints the calibration of
the pH electrode (command CAL pH) is essential; it is also recom-
mended for all other pH titrations. As least two buffers should be used
for the calibration; these should cover the expected measuring range.
For concentration direct measurements with ISE electrodes the sen-
sor must be calibrated with a series of standards (CAL Conc). During
the sequence the calibration data is stored automatically together with
the sensor data for the used sensor.
Under Calibration parameters you can edit the parameters for the
calibration sequence. These are identical for pH calibrations and ISE
calibrations. In the command CAL pH you must define the calibration
buffers, in the command CAL Conc the concentrations of the stan-
dards.
• Signal drift (d): Drift, i.e. the alteration in the measured value per
minute that has to be reached for measured value acceptance. off
means that the measured value acceptance takes place when the
maximum waiting time has elapsed. This may be advisable if the
electrode has a very slow response.
• Waiting time min. (d): The measured value is not accepted until
the minimum waiting time has elapsed, even if the measured value
drift has already been reached. The minimum waiting time is only
important for drift-controlled measurements.
• Waiting time max. (d): If the signal drift is switched off or has not
yet been reached then the measured value will be accepted after
the maximum waiting time has elapsed. If the waiting time has not
been newly entered then a waiting time that is suitable for the drift
will be calculated automatically according to the following equation:
5 0.01 Drift 150/ time Waiting + + =
• Temperature (d): Manually entered calibration temperature. If a
temperature sensor is connected and temperature measurement is
set to automatic or continuous under Sensor (see Section 4.1.5)
then the temperature will be measured. If off is defined then the
temperature is requested after the start (except the calibration is
carried out with a Sample Processor).
• Sample Processor (d): If the calibration is carried out with a Sam-
ple Processor then the buffers or standards are changed automati-
cally. That is why there is no request of the calibration temperature
at the start of the calibration. The value entered above is used.
For calibrations with a Sample Processor connected via a remote
box the parameter Remote must be activated. When the measure-
ment of a buffer or standard has been completed the Titrando
sends a signal to the Sample Processor via the remote connection
(EOD, see Section 6.2.2). The Sample Processor then switches to
the next buffer or standard.