The level of the acidometer and the accuracy of the instrument are two different concepts, and the level of the instrument is not exactly the same as its accuracy. The level of the acidity meter is indicated by the division value (resolution or minimum display value) of its indicator (abbreviated as electrometer), for example, the instrument with the division of 0.1pH is called the 0.1 level instrument; the minimum display value is 0.001pH The instrument is called the 0.001 level instrument, and so on. The accuracy of the instrument is the total error of the standard solution of the electrometer and the electrode matching test. It is not only related to the electrometer, but also relates to the glass electrode and the reference electrode. Demands from the actual starting point, the meter divides the value of 0.1 ~ 0.001pH, if necessary, according to the current state of science and technology, can produce more sophisticated electricity meter. However, due to structural and manufacturing reasons, the performance of the commonly used electrodes can not reach the completely ideal level.
The repeatability error of the glass electrode and the solution junction potential stability of the reference electrode are not better than 0.01pH. Therefore, the high resolution of the meter, the instrument test accuracy is difficult to better than 0.01pH. However, choosing a high-resolution instrument can maximize or eliminate the effects of the meter on the test error. As the electric meter to achieve satisfactory accuracy has not been a problem, so the instrument is intelligent, humane, reliable, easy to operate and cost-effective continuous innovation and improvement. The relationship between the level of the pH meter and its test accuracy is specified in the National Metrology Verification Protocol for Acidity Meter (JJG 119-84) as follows:
PH acidity meter level 0.2, 0.1, 0.02, 0.01, 0.001
Divide the value or the minimum display value (pH) 0.2,0.1,0.02,0.01,0.001
Electric meter indication error (pH) ± 0.1, ± 0.05, ± 0.01, ± 0.01, ± 0.002
The total error (pH) of the supporting test shows ± 0.2, ± 0.1, ± 0.02, ± 0.02, ± 0.01
Note: The test range of the auxiliary test should be controlled within the range of pH3 ~ pH10. As can be seen from the table above, for the following 0.01 acidity meter, the total value of the total error is equal to its level, for the 0.01 acid meter, the total error of 0.02pH, 0.001 for the acidity meter, the total error of indication Can only reach ± 0.01pH, but at this time need to use a pH standard material can be guaranteed. (Note: pH national standard substances are divided into two levels and two levels, the general pH meter is commonly used in two pH standards.)
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