VWR 662-2351, Инструкция по эксплуатации

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VWR Collection PH-130 pH-meter instruction manual v1.0x
10. CALIBRATION
Before starting measurement with a new electrode or before making
measurements, which require high accuracy, the electrode connected with
the meter should be calibrated. Results of the measurements made without
the calibration will be burdened with a significant error. Calibration is made in
buffer solutions of strictly defined values. It is based on comparing the
buffer’s value with the value displayed by the meter and next in automatic
introduction of correction which is taken into consideration during next
measurements. Calibration should be periodically repeated because the
electrode’s parameters may change during exploitation, what influences the
accuracy. The frequency of this procedure depends on the demanded
accuracy, the number of the measurements carried out, conditions in which
the electrode was used, temperature and value of the measured solutions. In
order to obtain good calibration results, the values of the applied buffers
should be compliant with the default values in the meter. During the
calibration process, after inserting the pH electrode and the temperature
probe into the buffer, the meter detects the buffer’s value.
When the highest accuracy is required, it is recommended to use fresh and
certified buffer solutions.
The temperature affects the buffer solutions pH value. In order to provide pH
buffer value corresponding to the default value in the meter, during the
calibration process the buffer’s temperature has to be equal 20
o
C.
If the electrode symbol turns yellow after the calibration is finished, it informs
that the electrode lost its efficiency and will have to be replaced soon. An
additional information is shown on the electrode calibration points screen
(description in the chapter 11).
Calibration in one solution does not guarantee high accuracy. If the accuracy
requirements are not very high and the measurement is made in the whole
measuring range one-point calibration should be made with use of 7.00 pH
buffer solution. Thanks to this the error connected with the offset of the
electrode will be eliminated.
At the rest of the points standard electrode’s slope parameters from the
meter’s memory will be adopted. This slope corresponds to the theoretical
efficiency of pH electrode. In case of accurate measurements in the whole
range we recommend three-point calibration. In case of measurements in
acids calibration in 2 buffer solutions: 4.00 and 7.00 pH is recommended, in
case of alkali measurements calibration in 7.00 and 10.00 pH buffers is
advisable. In
PH-130 the electrode characteristic is approximated linearly
between the calibration points.
Entering the calibration mode erases the stored electrode’s
characteristic.
The erased characteristic is signalised by the red colour of the symbol.