Classification and grade accuracy of acid-base concentration meter
According to the needs of production and life, people have scientifically researched and produced many types of acidity meters:
According to measurement accuracy
It can be divided into 0.2 level, 0.1 level, 0.01 level or higher precision.
According to the volume of the instrument
It is divided into pen type (mini type), portable type, desktop type and online type for online continuous monitoring and measurement.
According to the requirements of use
Pen-type (miniature) and portable pH meters are generally used by inspectors to bring them to the site for inspection.
The accuracy level of the pH meter is selected according to the accuracy required by the user for measurement, and then various shapes of pH meters are selected according to the convenience of the user.
◆According to portability, it can be divided into: portable pH meter, desktop pH meter and pen pH meter.
◆According to the application, it is divided into: laboratory pH meter, industrial online pH meter, etc.
◆According to the advanced level, it can be divided into economical pH meter, intelligent pH meter, precision pH meter or pointer pH meter and digital display pH meter.
◆The pen-type pH meter is generally made into a single range and has a narrow measurement range. It is a special and convenient instrument.
Portable and desktop pH meters have a wide range of measurement and are commonly used instruments. The difference is that the portable pH meter uses DC power supply and can be carried to the site. The laboratory pH meter has a wide measurement range, multiple functions and high measurement accuracy.
Industrial pH meters are characterized by good stability, reliable operation, certain measurement accuracy, strong environmental adaptability, and strong anti-interference ability. They have analog meter output, digital communication, upper and lower limit alarm and control functions, etc.
level accuracy
The level of the acidity meter and the accuracy of the instrument are two different concepts, and the level of the instrument is not completely consistent with its accuracy. The level of the acidity meter is expressed according to the graduation value (resolution or minimum display value) of its indicator (referred to as the electric meter), for example: an instrument with a graduation of 0.1pH is called a 0.1-level instrument; the minimum display value is 0.001pH The instruments are called class 0.001 instruments, and so on. The accuracy of the instrument is the comprehensive error of the electrometer and the electrode matching test standard solution, which is not only related to the electrometer, but also more related to the glass electrode and the reference electrode. Starting from the actual use requirements, the division value of the electric meter is 0.1~0.001pH. If necessary, a more precise electric meter can be produced according to the current technological level. However, due to structural and manufacturing reasons, the performance of commonly used electrodes cannot reach a completely ideal level.
Neither the repeatability error of the glass electrode nor the stability of the solution junction potential of the reference electrode is better than 0.01pH. Therefore, no matter how high the resolution of the electrometer is, the test accuracy of the instrument is difficult to be better than 0.01pH. However, choosing a high-resolution instrument can overcome or eliminate the influence of the electric meter on the test error to the greatest extent. Since it is not a problem to make the electric meter achieve satisfactory accuracy, it is constantly innovating and improving in terms of intelligence, humanization, reliability, easy operation and cost performance of the instrument. The relationship between the level of the acidity meter and its test accuracy is stipulated in the National Measurement and Verification Regulations for the acidity meter (JJG119-84) as follows:
PH acidity meter instrument level 0.2, 0.1, 0.02, 0.01, 0.001
Graduation value or 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
Supporting test indication total error (pH) ±0.2, ±0.1, ±0.02, ±0.02, ±0.01
Note: The test range of the matching test should be controlled within pH3~pH10. It can be seen from the above table that for the acidity meter below 0.01 grade, the total error value of the indication is equal to its grade; for the acidity meter of 0.01 grade, the total error of the indication value is 0.02pH; It can only reach ±0.01pH, and at this time, it is necessary to use a primary pH standard material to be guaranteed. (Note: There are two types of pH national standard materials, primary and secondary. Generally, the pH meter commonly used is the secondary pH standard material.)
