What Is a Digital pH Meter?

pH meter refers to the instrument used to determine the pH value of a solution. The pH meter works on the principle of a primary cell. The electromotive force between the two electrodes of the primary cell is based on Nerns' law, which is related to both the electrode's own properties and the hydrogen ion concentration in the solution. There is a corresponding relationship between the electromotive force of the primary battery and the hydrogen ion concentration, and the negative logarithm of the hydrogen ion concentration is the pH value. The pH meter is a common analytical instrument and is widely used in agriculture, environmental protection and industrial fields. Soil pH is one of the important basic properties of soil. Factors such as temperature and ionic strength of the solution to be measured should be considered in the pH measurement process. ^[1]

PH meter

pH meter refers to the instrument used to determine the pH value of a solution. The pH meter works on the principle of a primary cell. The electromotive force between the two electrodes of the primary cell is based on Nerns' law, which is related to both the electrode's own properties and the concentration of hydrogen ions in the solution. There is a corresponding relationship between the electromotive force of the primary battery and the hydrogen ion concentration, and the negative logarithm of the hydrogen ion concentration is the pH value. The pH meter is a common analytical instrument and is widely used in agriculture, environmental protection and industrial fields. Soil pH is one of the important basic properties of soil. Factors such as temperature and ionic strength of the solution to be measured should be considered in the pH measurement process. ^[1]

What is pH? pH is an abbreviation for the Latin word "Pondus hydrogenii" (Pondus =

According to the needs of production and life, people have scientifically researched and produced many types of acidity meters:

By measurement accuracy

It can be divided into 0.2, 0.1, 0.01 or higher precision.

By instrument volume

Divided into pen type (mini type), portable, desktop and online type for online continuous monitoring and measurement.

According to the requirements of use

The pen type (mini type) and portable pH pH meter are generally used by testers for on-site testing.

The accuracy level of the pH meter is selected according to the accuracy required by the user, and then various types of pH meters are selected according to the user's convenience.

According to the portability, it is divided into: portable pH meter, desktop pH meter and pen pH meter.

Divided by purpose: laboratory pH meter, industrial online pH meter, etc.

According to the advanced level, it can be divided into economic pH meter, intelligent pH meter, precision pH meter or pointer pH meter and digital pH meter.

Pen type pH meter is generally made into a single range with a narrow measurement range. It is a dedicated and simple instrument.

Portable and benchtop pH meters have a wide measurement range. Commonly used instruments, the difference is that the portable uses DC power and can be carried to the scene. The laboratory pH meter has a wide measurement range, multiple functions, and high measurement accuracy.

The characteristics of industrial pH meter are good stability, reliable operation, certain measurement accuracy, strong environmental adaptability, and strong anti-interference ability. It has analog output, digital communication, upper and lower limit alarm and control functions.

Level of the pH meter and instrument

With the development of scientific research and the advancement of production technology, the quantitative analysis of moisture has been listed as one of the basic items of physical and chemical analysis of various substances as an important quality indicator of various substances.

According to the different moisture content in different types of samples, different requirements for measuring moisture are proposed. Moisture measurement can be the control analysis of industrial production, or the quality certification of industrial and agricultural products; the water content can be measured from products in tons.

Before proceeding, check the integrity of the electrodes. Calomel electrode . Since composite electrodes are widely used, the following mainly discusses composite electrodes.

There are mainly two types of compound electrodes used in the laboratory: fully-enclosed and non-enclosed. There are relatively few fully-enclosed types, which are mainly produced by foreign companies. Before using the composite electrode, first check whether the glass bulb is cracked or broken. If not, use a pH buffer solution to perform two-point calibration. When the positioning and slope buttons can be adjusted to the corresponding pH value, it is generally considered to be usable, otherwise you can press Instruction manual for electrode activation treatment. The activation method is to soak in a 4% hydrogen fluoride solution for about 3 to 5 seconds, take it out and rinse it with distilled water, and then soak it in a 0.1mol / L hydrochloric acid solution for several hours, rinse it with distilled water, and then calibrate it, that is, use the pH value. Position the buffer solution for 6.86 (25 ° C). After adjusting, select another pH buffer solution to adjust the slope. If it cannot be adjusted, you need to replace the electrode. For non-closed composite electrodes, an external reference solution, that is, a 3 mol / L potassium chloride solution, is added inside, so you must check whether the potassium chloride solution in the electrode is above 1/3. If not, add 3 mol / L. Potassium chloride solution. If the potassium chloride solution exceeds the position of the small hole, shake off the excess potassium chloride solution, so that the solution is located below the small hole, and check whether there are air bubbles in the solution. If there are air bubbles, flick the electrode and drive the air bubbles out completely.

During use, the rubber on the electrode should be peeled off, so that the small holes are exposed. Otherwise, a negative pressure will be generated during the analysis, which will cause the potassium chloride solution not to pass through the glass bulb and perform ion exchange smoothly. Will make the measurement data inaccurate. After the measurement is completed, the rubber should be restored and the small hole should be sealed. After the electrode is washed with distilled water, it should be immersed in a 3 mol / L potassium chloride solution to keep the electrode bulbs wet. If the electrode is found to have lost the protective solution before use, it should be immersed in a 3 mol / L potassium chloride solution. Hours to achieve the best measurement of the electrode. In actual use, it is found that some analysts treat the composite electrode as a glass electrode and soak it in distilled water for a long time. This is incorrect, which will greatly reduce the concentration of potassium chloride solution in the composite electrode, resulting in The electrode response is not sensitive during the measurement, which eventually leads to inaccurate measurement data. Therefore, the composite electrode should not be immersed in distilled water for a long time.

There are two ways to install the pH meter: flow-through and immersion.

The sewage treatment plant generally uses immersion installation. For example, the pH meter of the sewage treatment plant is installed in the overflow overflow tank of the grit chamber. The pH value here is more representative and the water flow is stable. Cause a big impact. Regular maintenance helps the meter to measure accurately and prolong the life of the meter. It should be noted that the special cable between the sensor and the transmitter must not be wet, otherwise the high-resistance and low-voltage signal of the electrode will not be transmitted to the transmitter.

If the electrode is not measured, the yellow protective sleeve should be put on, which can keep the electrode in a wet state, which is conducive to extending the service life of the electrode. Every other month or so, the electrode should be cleaned. First, use a gentle stream of water to spray the attachments, then immerse the electrode in the cleaning solution for a period of time, and then wash it with water.

The sensor bracket should also be cleaned. After each cleaning, the buffer solution should be used for calibration. The manufacturer generally provides two bottles of standard solution, one bottle is equal to 7 for calibration of the instrument zero point; one bottle is equal to 4 for calibration of the instrument's signal output slope .

How to choose a pH meter | acidity meter | acidity meter? Five points should be noted.

When choosing an acidity meter, we must first consider the application, choose a pen pH meter, portable acidity meter, desktop acidity meter, or industrial pH meter; secondly, consider the accuracy required for the measurement, and choose the accuracy that is suitable for your use. BpH -200A type pH meter is widely used in industrial, electric power, agriculture, medicine, food, scientific research and environmental protection. This instrument is also a necessary inspection equipment in the QS and HACCP certification of food factories and drinking water factories.

We need to consider the following points when purchasing acidity timers:

1. According to the application, it can be divided into: pen pH meter,

(1) Prepare two suitable pH standard solutions, pH4.01PH6.86 or PH9.18, in the laboratory, and select the standard solution according to the fluctuation range of the water sample on site. If the on-site water quality is often acidic, choose two standard samples of PH4.01 and PH6.86; if the on-site water quality is often alkaline, choose two standard samples of PH6.86 and PH9.18.

(2) Take out the sensor from the scene, and clean the glass electrode of the probe with water.

(3) Pour the two standard solutions into two prepared beakers.

(4) Immerse the electrode in the first standard solution, open the meter menu, and calibrate the first point. The operation method of the calibration menu is different for different brands of meters. Operate according to the instruction manual.

(5) After the first point calibration is passed, rinse the electrode with water, then place the electrode in the second standard solution, turn the meter menu, and calibrate the second point.

(6) After the two-point calibration is completed, meters of different brands will show whether the meter has passed the calibration or is qualified in different ways.

(7) If it passes, put the electrode back into the test liquid, and put the meter into operation.

(8) If the instrument calibration fails, repeat the above procedure to calibrate it again. If it fails, replace the pH electrode. The pH electrode life is generally about two years.

What is the difference between different pH sensitive glass membranes?

From the perspective of shape, the pH-sensitive glass film can be made into various shapes such as spherical, cylindrical, flat, and tapered, mainly to match the shape of the measured medium. Such as spherical and cylindrical, mainly used for liquid media; flat shape is mainly used for semi-solid media containing water, such as skin, meat, leather, paper, etc .; tapered cone is mainly used to penetrate the medium for measurement, such as soil, fruits Wait. The difference is even greater in terms of composition. There are sensitive glass films for general use, sensitive glass films for high temperature use, sensitive glass films for strong acid or alkali use, and ones for high temperature steam disinfection (130 ° C). Sensitive glass film, and sensitive glass film for low temperature and low ionic strength, etc. Some inaccurate or unstable pH tests have a lot to do with the improper selection of pH sensitive glass membranes.

Industrial pH meter

Using a pH meter can better control chemical reactions, and achieve the goals of improving productivity and product quality, and safe production. The pH measurement system with automatic recording also provides evidence of litigation against pollution hazards. Some batch production processes (such as some fertilizer production, food processing) can be changed to continuous production after using a pH meter. In modern industry, pH meters are used more than the sum of other types of continuous analytical instruments. A pH meter is required in almost every production sector that requires water. Its applications range from industrial water and waste treatment to flotation processes in mining, including a wide range of fields including pulp and paper, metal processing, chemicals, petroleum, synthetic rubber production, power plants, pharmaceuticals, and food processing.