- 22 -
User‘s manual for CP-511 pH meter v1.10
Depending on the kind of measured solution or substance, appropriate kind
of electrode should be chosen. They differ one from another with shape,
membrane’s look, kind of junction and body. Electrode for heavily polluted
sewage is different than this for clean water or for meat or soil. Using
unsuitable electrode for measurements may cause its damage and make
next measurements impossible.
Results of multiple pH measurements of the same solution with stabile
temperature may differ one from another. When analysing this situation, the
factors given below should be taken into consideration:
- the differences may occur because of using electrode of not very good
quality;
- the result was treated as stabilised too soon (the time of stabilisation of an
average-quality electrode is about 40 s.);
- the measured solution may not be homogeneous and without using the
electromagnetic stirrer the results won’t be equal;
- during measurements of sewage the result may be changed by chemical
reactions.
Slight differences of the results are connected with the accuracy of the meter.
The accuracy of CP-511 is ±0,01 pH, ±1 digit, what practically means that in
extreme conditions results of two measurements of the same solution may
differ in ±0,05 pH. This is an acceptable error, because one result has error
equal – 0.02 and the second one + 0,02 pH. Expression ±1 digit in the
technical data takes into consideration another possible difference which
arises because of so called discretisation error – number of digits displayed
on the LCD.
Sometimes the accuracy of calibration is checked in another buffer solution.
In case of performing two-point calibration in 7,00 pH and 4,00 pH buffer
solutions and the accuracy of such calibration is checked in 10,00 pH buffer
in some cases the result may be 9,90 pH or 10,10 pH. Such difference is
possible when the slope of the electrode isn’t symmetrical to 7 pH.
Using three-point calibration in neutral, alkali and acidic buffer solutions may
prevent such a situation.
To Next Page
Loading...
