Familiar with pH detectors and pH transmitters

I understand the pH detector to be the basic principle of pH measurement with an acidometer. Probably the most familiar and oldest zero-current measurement method used to determine the chemical reaction process is pH measurement. What is pH and what should you know about pH measurement? Generally speaking, pH measurement is used to determine the acidity or alkalinity of a certain solution. Adding acid to water increases the acidity of the water and decreases the pH value. Adding alkali to water will increase the alkalinity of the water, and the pH value is the unit used to express acidity and alkalinity. When we say that milk is "cool" or that acid is "weak", we are not definitely indicating the state of things. This is because we do not state the unit of measurement and the value of the measurement. When we say that the temperature of milk is 10°C, it is an exact concept. Similarly, when we say that the pH value of a weak acid is 5.2, this is also an accurate concept. There are a wide variety of acids and bases in the world with varying strengths. For example: Hydrochloric acid is a very strong acid, while boric acid is very weak (and can be used to rinse eyes and wounds). The strength of an acid depends mainly on the number of hydrogen ions dissociated in the solution. In strong acids, hydrogen ions dissociate widely, while in weak acids, they dissociate very rarely. The reason why hydrochloric acid becomes a strong acid is because the chlorine almost completely dissociates the hydrogen ions. Boric acid is a weak acid because very few hydrogen ions dissociate. Even chemically pure water is dissociated in trace amounts: Strictly speaking, hydrogen nuclei do not exist in a free state until they hydrate with water molecules. H2O+H2O=H3O-+OH- Since the concentration of hydronium ions (H3O) can be regarded as the same as the concentration of hydrogen ions (H), the above formula can be simplified into the following commonly used form: H2O=H++OH- The positive hydrogen ion here is expressed as "H+ ion" or "hydrogen nucleus" in chemistry. Hydronium nuclei are represented as "hydronium ions". Negative hydroxide ions are called "hydroxide ions". Using the law of mass action, an equilibrium constant can be found to express the dissociation of pure water.: K= H3O+·OH- H2O Since only a very small amount of water is dissociated, the molar concentration of water is actually a constant, and there is an equilibrium constant K that can be used to calculate the ion product KW of water. KW=K×H2O KW = H3O+·OH-=10-7·10-7=10mol/l (25℃) In other words, for one liter of pure water at 25℃, there are 10-7 moles of H3O- ions and 10-7 moles of OH- ions. In order to avoid calculations with the negative Pluto-exponent of this molar concentration, biologist Soernsen proposed in 1909 to replace this inconvenient value with a logarithm and define it as "pH value". Mathematically, pH is defined as the negative of the common logarithm of the hydrogen ion concentration. Right now: pH=-logH+ Strictly speaking, this formula ignores the interaction between hydrogen ions (H+) and hydroxide ions (OH-), because the electric field force between ions significantly reduces the activity of the ions. That is to say: The active concentration (i.e. activity) of hydrogen ions is also related to all other ions being dissolved. For example: When the hydrogen ion concentration is 10-1 mol/1, the theoretical pH value should be 1.0, but we only measured the pH value to be 1.08. This shows that the degree coefficient f≠1, but 0.823. That is, the exact definition of pH should be: Temperature coefficient of pH measuring solution: Since the ion product is highly dependent on temperature, the neutral point of pure water has the following distribution: 0℃ = pH 25℃ = pH 75℃ = pH 100℃ = pH Acids and bases are diluted with water, and there will certainly be cases where the pH value depends on temperature as mentioned above. For strong acids, the effect of water's self-dissociation is zero, and the pH is determined solely by the dissociation of the acid.: At 0℃, at 25℃, at 50℃, 0.001nHCL 3.00 pH 3.00 pH 3.00 pH 0.1n HCL 1.08 pH 1.08 pH 1.08pH For alkaline solutions, the above influence is great. Since the activity of hydrogen ions is reduced at this time, the self-dissociation of water has an advantage. At 0℃, at 25℃, at 50℃, 0.001nNAOH 11.94pH 11.00pH 10.26pH Saturated lime water ┄┄ 12.4 pH 11.68pH For practical purposes, there are the following conclusions:: For process control of the pH value, the temperature characteristics of the solution must also be known ； The pH values ​​of the measured media can only be compared when they are at the same temperature. How to Measure pH Almost everyone knows how to measure using litmus paper or the property of changing color with different pH levels. For example: Litmus paper turns dark or light red in acid solution, and turns dark or light blue in alkaline solution. However, this method will cause obvious errors (≤2PH value) in weak buffers, solutions containing metal ions, or organic compound solutions. In order to obtain accurate and reproducible pH values, potentiometric analysis is used for pH measurement. PH Transmitter 1. Product Introduction The two-wire PH transmitter is a new product that our company introduces glass electrodes and detection circuits from the American BJC Company, and is matched with a variety of new structural materials. This product can detect the pH of solutions in chemical, petroleum, oil refining, chemical fiber, textile, rubber, papermaking, tobacco and alcohol, sugar, food, mining, smelting, steel, power generation, pharmaceuticals, water treatment, military and other industries. Main features: 1. Special high impedance converter. The instrument measurement part adopts a strict and special packaging process to ensure an input impedance of up to 3×1012Ω. Even in harsh working environment conditions, it can ensure accurate and stable measurement of PH signals. 2. The measuring range can be adjusted arbitrarily within the pH value of 0~14. 3. Intelligent four-wire products use power supply and signal isolation technology between the measurement circuit and the output circuit to improve the anti-interference ability and can be directly connected to PLC and DCS control systems. 4. Adopt a variety of structural types, a variety of materials, and adopt anti-corrosion sealing and other measures to make the instrument not only beautiful, compact, lightweight, corrosion-resistant and waterproof, but also easy to install under various environmental conditions. 5. Equipped with various types of composite glass electrodes imported from the United States, the potential is stable and reliable, and suitable for measurement of various media. 6. Fully automatic temperature compensation. 7. Two-wire or four-wire wiring, 4~20mA output, strong load capacity, long signal output distance. 8. With on-site display, easy for on-site installation and debugging ； The analog type can display the PH value, and the intelligent type can display the PH value and temperature value. 2. Main technical indicators 1. Measurement range: 0-14pH optional 2. Instrument stability: ±0.05pH/48 hours 3. Measurement error: soil 0.1pH 4. Instrument resolution: 0.01pH 5. Input impedance: Greater than 3×1012Ω 6. Output signal: 4～20mA． DC ； 7. Output load resistance: 0～500Ω (250Ω with digital meter) 8. Measurement conditions: Medium temperature: -10～140℃(determined by sensor) Medium pressure: General use

To put it simply, one is an analytical instrument and the other is online analysis. I don’t know if I am right.