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User‘s manual for CP-511 pH meter v1.10
8. Calibration
Before starting measurement with new electrode, after long-lasting use or
before making measurements which require high accuracy the electrode
connected with the meter should be calibrated. Results of measurements
made without calibration will be burdened with a significant error. Calibration
is made in buffer solutions. It consists in comparing pH value of buffer
solutions 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
parameters of the electrode are changing while working, what influences
accuracy. The frequency of this procedure depends on the demanded
accuracy, number of the measurements carried out, conditions in which the
electrode was used, temperature and value of the measured solutions. When
the highest accuracy is required, it is recommended to use fresh buffer
solutions with certificates.
CP-511 enables calibration in buffer solutions with values determined by
the manufacturer, which are: 4.00; 7.00 and 10.00 pH, and are
automatically detected.
There is a possibility of calibration minimum in 1 point and maximum in 3
points. The more calibration points are used, the higher accuracy in the
whole range is ensured.
Calibration at 1 point does not ensure 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 so called “zero 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 CP-511 the slope of the electrode is approximated in segments between
the calibration points.
Starting the calibration process irreversibly erases the calibration data
stored in the memory.
The buffer solutions may be used in a freely chosen order.
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