Classification of pH meters and level of accuracy
According to the measurement accuracy
Can be divided into 0.2 grade, 0.1 grade, 0.01 grade or higher precision.
According to the volume of the instrument
There are pen type (mini type), portable type, desktop type, and on-line type with on-line continuous monitoring and measurement.
According to the requirements of use
Pen-type (mini) and portable pH meter is generally used by inspectors to bring to the site testing.
The accuracy level of the pH meter is selected based on the accuracy required for the user's measurement, and then various shapes of pH meters are selected based on the user's ease of use.
◆ According to the portability, it is divided into: portable pH meter, desktop pH meter and pen pH meter.
◆ According to the use, they are divided into: laboratory pH meter, industrial on-line pH meter and so on.
◆ According to the advanced degree is divided into economic pH meter, intelligent pH meter, precision pH meter or divided into pointer pH meter, digital pH meter.
◆ Pen-type pH meter, generally made of a single range, narrow measurement range, for the special simple instrument.
Portable and desktop pH meter measuring range is wider, commonly used instruments, the difference is that the portable DC power supply, can be carried to the scene. Laboratory pH meter measuring range, multi-functional, high precision measurement.
Industrial pH meters are characterised by good stability, reliable work, a certain degree of measurement accuracy, environmental adaptability, anti-interference ability, with analogue ri output, digital communication, upper and lower limits of the alarm and control functions.
Level accuracy
The level of acidity meter and the accuracy of the instrument are two different concepts, the level of the instrument and its accuracy is not completely consistent. Acidity meter level is according to its indicator (referred to as electrometer) of the graduation value (resolution or minimum display value) that, for example: graduation of 0.1pH instrument is called 0.1 level of instrument; minimum display value of 0.001pH instrument is called 0.001 level of instrument, and so on. The accuracy of the instrument is the meter and electrode supporting the test of the standard solution of the integrated error, which is not only related to the meter, but also with the glass electrode and the reference electrode is more relevant. From the practical use of the requirements of the scale value of the meter for 0.1 ~ 0.001pH, if necessary, according to the current level of science and technology, it is possible to produce a more precise meter. However, due to structural and manufacturing reasons, the performance of commonly used electrodes can not reach a completely ideal degree.
Repeatability error of the glass electrode and the reference electrode of the solution junction potential stability is not better than 0.01pH. Therefore, the resolution of the galvanometer is even higher, the accuracy of the instrument test is difficult to better than 0.01pH. However, the choice of high-resolution instruments can be maximised to overcome or eliminate the impact of the galvanometer on the test error. As to make the meter to achieve satisfactory accuracy is no longer a problem, so are in the instrument's intelligent, user-friendly, reliable, easy to operate and cost-effective and other aspects of continuous innovation and improvement. Acidity meter level and its test accuracy of the relationship between the acid meter in the national metrological verification regulations (JJG119-84) in the following provisions:
PH acidity meter instrument level 0.2 level, 0.1 level, 0.02 level, 0.01 level, 0.001 level
Graduated value or minimum display value (pH) 0.2, 0.1, 0.02, 0.01, 0.001
Meter display value error (pH) ±0.1, ±0.05, ±0.01, ±0.01, ±0.002
Matching test total error (pH)±0.2,±0.1,±0.02,±0.02,±0.01
