Thermocouple basics, what are the basic principles of thermocouples?

With the promulgation and implementation of China's 2010 new version of GMP, the majority of pharmaceutical companies have more development, but also brought new competitive pressure, especially for product quality management has higher requirements, for many enterprises, to improve product quality management, enhance the core competitiveness of enterprises, successfully pass the new version of GMP certification, imminent. With the implementation of the new version of GMP, the temperature verification requirements for pharmaceutical equipment in pharmaceutical factories are becoming more and more stringent, and the requirements for the performance of temperature verification systems in pharmaceutical factories are also becoming more and more stringent. In order to meet the needs of temperature verification of pharmaceutical companies, different temperature verification equipment has appeared on the market, including imported and domestic, as well as wired and wireless temperature verification systems

Thermocouple basics.

With the progress of the times, the application of temperature instruments is more and more extensive, and the use of thermocouples is also involved more and more, our company (Jiangsu Yokogawa automatic control equipment) is a main instrument production and sales company, the amount of thermocouples is gradually increasing, although thermocouples are very common instruments, but for some customers there are still a lot of questions and confusion, simply introduce the basic knowledge of thermocouples.

Thermocouples are two different conductors connected together to form a loop, and the so-called thermo-electromagnetic force is generated when the measuring and reference connection points are at different temperatures.

Connection point use.

The measuring connection point is the portion of the thermocouple connection point that is at the temperature being measured.

A reference connection point is a part of a thermocouple connection point that is maintained at a known temperature or automatically compensated for by temperature changes.

Note: In conventional industrial applications, thermocouple elements are typically terminated on a connector; However, the reference connection point is rarely located on the connector, and the appropriate thermocouple extension wire is used to transfer to a more stable temperature controlled environment.

The type of connection point.

The shell thermocouple connection point is physically connected (welded) to the probe wall, which allows for good heat transfer – i.e. heat is transferred from the outside through the probe wall to the thermocouple connection point. Shell thermocouples are recommended to measure the temperature of static or flowing corrosive gases and liquids, as well as some high-voltage applications.

In insulated thermocouples, the thermocouple connection points are separated from the probe wall and surrounded by a soft powder. Although an insulated thermocouple responds more slowly than a shelled thermocouple, it provides electrical insulation. It is recommended to use insulated thermocouples for the measurement of corrosive environments, ideally to completely electrically insulate the thermocouple from its surroundings by means of a jacket shield.

Open-ended thermocouples allow the tip of the connection point to penetrate deep into the surrounding environment, and this type provides the best response time, but is limited to non-corrosive, non-hazardous and non-pressurized applications.

Extension lines. A thermocouple extension is a pair of wires that have the characteristics of electromagnetic frequencies at the same temperature as the thermocouple to which they are attached. When the connection is appropriate, the extension wire transfers the reference connection point from the thermocouple to the other end of the line, which is typically located in the controlled environment.

Select a thermocouple.

The following factors should be considered when selecting a thermocouple:

The medium to be measured. The temperature range to be measured.

Required response time.

The type of connection point.

Chemical resistance of thermocouple or jacket materials.

Resistance to wear or vibration.

Thermocouple is a commonly used temperature measuring element in temperature measuring instruments, which is composed of two conductors of different compositions at both ends to form a loop, when the temperature of the thermocouple at the junction is different, a thermal current will be generated in the loop. If there is a temperature difference between the working end of the thermocouple and the reference terminal, the display meter will indicate the temperature value corresponding to the thermoelectric potential generated by the thermocouple. The thermoelectric heat of the thermocouple will increase with the temperature of the measuring end, and its size is only related to the thermocouple material and the temperature at both ends, and not the length and diameter of the thermoelectrode.

The shape of various thermocouples is often very different depending on the need, but their basic structure is roughly the same, usually composed of the main parts such as the thermode, the insulating sleeve protection tube and the junction box, and is usually used with display instruments, recording instruments and electronic regulators.

The fundamental law of thermocouples is not three, but four:

1. The law of homogeneous conductors.

A closed loop consisting of two welds of the same homogeneous material (conductor or semiconductor) will not produce a contact potential regardless of the conductor cross-section and temperature distribution, and the temperature difference potential will cancel each other, and the total electric potential in the loop will be zero.

2. The law of intermediate conductors.

When an intermediate conductor (third conductor) is connected to a thermocouple loop, as long as the temperature at both ends of the intermediate conductor is the same, the introduction of the intermediate conductor has no effect on the total potential of the thermocouple loop, which is the law of the intermediate conductor.

3. The law of intermediate temperature.

The thermoelectric potential between the two contacts (temperature t, t0) of the thermocouple circuit is equal to the algebraic sum of the thermocouple's thermoelectric potential at temperatures t, tn and the thermoelectric potential at temperatures tn and t0. tn is called the intermediate temperature.

4. Refer to the electrode law.

The simple explanation is: use high-purity platinum wire as a standard electrode, assuming that the positive and negative electrodes of the nickel-chromium-nickel-chromium thermocouple are paired with the standard electrode respectively, and their values add up to the value of this nickel-chromium-nickel-chromium.

Thermocouples work by using two different materials to close a circuit; When the temperature of the two ends is different, there will be a current; The temperature of the medium can be easily obtained by means of a measuring instrument.

It is important to emphasize that thermocouple temperature measurement, in the final analysis, is to measure the thermal electromotive force at both ends of the thermocouple. The measuring instrument allows us to see the temperature value because it has converted the thermal electromotive force into temperature.

Applications of thermocouples:

Thermocouples are commonly used to measure temperature in temperature measurement and are passive devices. It is often used in places that require automatic temperature control, such as food machinery, packaging machinery, industrial furnaces, automation engineering, etc.

The thermocouple needs to be used with a thermostat to achieve automatic temperature control. It is used in a wide range of applications wherever automatic temperature control is required. For example:

Food machinery, rubber machinery, glass machinery, shoe machines, packaging machinery, as well as industrial furnaces, automation engineering and so on.

The above content reference: Encyclopedia - Thermocouples.

The principle of operation is that when a thermocouple is heated, it generates a thermoelectric potential that allows the solenoid valve to work. The working principle of the specific gas stove is as follows: when the knob is pressed and the small fire is ignited, the thermocouple is heated by its flame to produce a thermoelectric potential.

The thermoelectric potential is introduced into the solenoid coil through the wire, and the magnetic field is generated to make the solenoid valve engaged, the gas valve is opened, and the combustion path is opened to maintain its normal combustion. Thermocouple for flameout protection of thermoelectric gas appliances, which includes the use of armored single-core structure, the shell as the positive electrode, and its top end is welded together with the central electrode (negative electrode), which is characterized by the use of nickel-chromium alloy, and the central electrode (negative electrode) is made of high-temperature aluminized or high-temperature silicon-infiltrated constantan alloy on the surface. The present invention utilizes advanced processing technology, not only produces a sufficiently high thermoelectric potential, but also improves the anti-corrosion and anti-aging performance of the alloy, thereby improving the service life of the thermocouple.

In addition, it has the characteristics of low cost and wide use conditions.

The job of a thermocouple is to use the thermoelectric effect to measure temperature.

The galvanic couple is a commonly used temperature measuring element in temperature measuring instruments, which directly measures the temperature and combustion excitation, and converts the temperature signal into a thermal electromotive force signal, which is converted into the temperature of the measured medium through the electrical instrument (secondary instrument).

The shape of various thermocouples is often very different due to needs, but their basic structure is roughly the same, usually composed of main parts such as thermoelectrodes, insulating sleeve protective tubes and junction boxes, and is usually used with display instruments, recording instruments and electronic regulators.

The thermoelectric effect is produced by a circuit consisting of two conductors through a temperature difference. Two different conductors or semiconductors are at both ends, where the hot end is called the hot end or working end, and the other end is called the cold end or free end, due to the different temperatures at the two ends, an electromotive force will be generated in the loop, and the magnitude and direction of the virtual momentum are related to the conductor and temperature at both ends.

Technical advantages of thermocouples

The thermocouple has a wide temperature measurement range and stable performance; High measurement accuracy, the thermocouple is in direct contact with the measured object, and is not affected by the intermediate medium; The thermal response time is fast, and the thermocouple responds flexibly to temperature changes; The measurement range is large, and the thermocouple can continuously measure the temperature from -40 to 1600; The thermocouple has reliable performance and good mechanical strength. Tong Duan burn has a long service life and is a convenient device.

The galvanic couple must be composed of two conductor (or semiconductor) materials with different properties that meet certain requirements. There must be a temperature difference between the thermocouple measurement end and the reference end.

Conductors of two different materials or semiconductors A and B are soldered together to form a closed loop. When there is a temperature difference between the two attachment points 1 and 2 of conductors A and B, an electromotive force is generated between them, thus forming a large and small current in the circuit, a phenomenon called thermoelectric effect. Thermocouples work with this effect.

1.Thermocouples are commonly used temperature measuring elements in temperature measuring instruments. Measure the temperature directly, convert the temperature signal into a thermoelectric potential signal, introduce the signal into the control system, and convert it to 4-20mA to display the temperature through the temperature transmitter.

The basic principle of thermocouple temperature measurement is that when there is a temperature gradient at both ends, an electric current passes through two material conductors of different compositions, A and B. At this point, there is an electric potential-thermoelectric potential between the two ends, the so-called Seebeck effect.

3.The two joints of thermocouple electrode A and B are usually welded by arc welding, electrofusion welding, soldering and so on. The solder joints should be smooth, small in diameter, in good contact, and firm to improve the sensitivity and durability of the thermocouple.

4.A homogeneous conductor of two different compositions is a thermode, with a working end t at the high temperature end and a free end t at the low temperature end, usually at a constant temperature. The direction and magnitude of the electric potential are related to the conductor material and the temperature of the two connection points.

This phenomenon is known as the thermoelectric effect, and a circuit consisting of two conductors is called a thermocouple, and these two conductors are called thermoelectrodes, and the electric potential is known as thermoelectric potential. According to the functional relationship between thermoelectric potential and temperature, a thermocouple indexing table is made;

5.The thermopotential of a thermocouple is a function of the temperature function of the thermocouple's operating end, not the difference in temperature between the cold and working ends of the thermocouple. When the thermocouple material is homogeneous, it is only related to the composition of the thermocouple material and the temperature difference between the two ends.

When determining the material composition of the two thermocouple filaments of a thermocouple, the thermopotential of the thermocouple is only related to the temperature difference of the thermocouple; If the cold junction temperature of the thermocouple is kept at 1, the thermocouple's thermopotential is only a single value function of the temperature on the operating side.

1. Because the composition of the thermocouple is relatively simple, the operation and installation procedures are not so complicated, even if the thermocouple has problems and needs to be replaced, it is more convenient.

2. The different structures of thermocouples have different characteristics, and the compression spring thermocouple is slightly better in terms of seismic resistance and accuracy because of its special structure.

3. The thermocouple is resistant to high temperature, because the temperature in various environments is inducted, and the temperature tolerance range of the thermocouple is larger, even reaching more than 2000 degrees.

4. The durability of thermocouples is better, so its life is longer, and we can save a lot of costs.

Hello, the types of thermocouples used and their respective characteristics are: there are 7 kinds of thermocouples commonly used in industry: S, B, E, K, R, J, and T: (1) platinum rhodium 10 platinum thermocouple graduation number is S, temperature measurement range 0 1300, platinum rhodium wire is the positive electrode, pure platinum wire is the negative electrode; Platinum Rhodium-10 thermocouples are suitable for use in oxidizing and neutral media.

Because high-purity platinum and platinum-rhodium alloys are readily available, S-type thermocouples have high replication accuracy and measurement accuracy, so they are often used for precision temperature measurement and as standard thermocouples. Its disadvantages are that the thermoelectric potential is small, the thermoelectric properties are nonlinear, the ** is expensive, and it is susceptible to the erosion and deterioration of reducing gases and metal vapors at high temperatures, which causes changes in thermoelectric properties and affects the accuracy of measurement. (2) Nickel-chromium-nickel-silicon (nickel-aluminum) thermocouple, the graduation number is k, and the temperature measurement range is 200 1300; Nickel-chromium is the positive electrode and nickel-silicon is the negative electrode.

It is suitable for use in oxidizing or neutral media. When the medium temperature is lower than 500, it can also be used to measure the temperature in the reducing medium, in addition, its thermoelectric potential is large, the linearity is good, the measurement range is wide, the cost is moderate, it is the most commonly used thermocouple in industrial temperature measurement. The disadvantage is that the thermoelectric properties of nickel and aluminum are changed due to the oxidation and deterioration of nickel and aluminum during long-term use, which affects the measurement temperature.

3) nickel-chromium --- copper thermocouple, which is composed of nickel-chromium wire and copper-based (copper, nickel alloy) wire, with a division of E, and a measurement range of 200 1300; Nickel-chromium is the positive electrode, and copper is the negative electrode. It is suitable for measuring temperature in reducing medium or neutral medium, and is characterized by high thermoelectric sensitivity, which is convenient, but the measurement range is not large, the measurement temperature is not high, and the alloy wire of the copper wall is susceptible to oxidation and deterioration, because the material quality is hard and it is not easy to get a uniform wire diameter. (4) platinum rhodium 30 platinum rhodium 6 thermocouple, the graduation number is b, and the temperature measurement range is 0 1600; Platinum rhodium 30 wire (platinum 70%, rhodium 30%)

Questions. <>

What kind of filament is this filament in a thermocouple?

Nickel-chromium. Questions.

Is this kind of thing valuable?

It's worthless.

Questions. Thank you.