Thermocouples are made up of a combination of two different alloy materials

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For the sake of safety, the flame-out protection device of the gas stove is very necessary, and the relevant national standards also have mandatory provisions for this. However, some gas stoves still have ** accidents, and these products either do not have flame-out protection devices, or use extremely poor ignition devices. At present, there are three commonly used flameout protection methods on the market:

Thermal, thermoelectric and photoelectric. Let's take a closer look:

Thermal: also known as bimetal sheet type. Bimetal sheet is made of two metals with different expansion coefficients, under the action of temperature, the metal side with a large expansion coefficient will bend to the metal side with a small expansion coefficient, and when the temperature is lost, the metal that has been expanded and bent will slowly return to its original state, so the bimetal sheet is also called memory alloy.

Sensors that use bimetal as safety protection devices take advantage of the expansion and bending of bimetal sheets under the action of temperature.

The advantages of the bimetal protection device are its simple structure and low cost. The disadvantage is that it is difficult to install, and there are high requirements for the installation position of the bimetal sheet and the coordination of the plug valve and the gas valve, and the thermal inertia is large, the time to open and close the valve is long, and the service life is short.

Thermoelectric: This device also uses the heat energy generated when gas is burned. The thermoelectric flameout safety device is composed of two parts: a thermocouple and a solenoid valve, and the thermocouple is a combination of two different alloy materials.

Different alloy materials will produce different thermoelectric potentials under the action of temperature, and thermocouples are made by using different thermoelectric potentials generated by different alloy materials under the action of temperature, which makes use of the electrothermal difference of different alloy materials.

The thermoelectric safety protection device has simple structure, easy installation and low cost, and has been widely used. But this kind of protection device takes thermocouple as thermal sensor, and the disadvantage is that the thermal inertia is large, the reaction speed is slow, makes people feel that the operation is inconvenient, and the service life is short, and the matching installation accuracy of the plug valve and the solenoid valve is required to be higher.

Photoelectric type: also known as ion induction type. The device uses gas, and when burning, the flame carries ions and has unidirectional conductive characteristics.

This safety protection method was first applied to gas water heaters, and has been developed from the early DC induction to the current AC induction, so that the reliability has been greatly improved, and the application in the stove is only three or four years old.

In addition, the ignition of the gas stove is required to be lit 10 times in a row, and at least 8 times can be ignited during the test; However, the ignition used by poor quality enterprises may only be lit five or six times 10 times in a row, if so, because the fire is not lit, the gas will leak out, and the leakage will be too much, and when it is lit again, it will deflagrate, thus injuring people. Some unscrupulous enterprises use inferior igniters, the reason is for cost considerations, the cost of a good igniter is 20 to 30 yuan, and the ignition of poor quality is about 10 yuan.

Platinum rhodium alloys, nickel-chromium, copper-nickel, iron-nickel, nickel-chromium-silicon, nickel-chromium.

The thermocouple is made of () metal material, which converts the Wenchang regret void forward impulse into flame resistance into thermal electromotive force.

a.A. b.Both are the same.

c.Two different.

d.Three kinds. Correct answer: Two different ones.

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.

The thermal first banquet potential of a thermocouple is mainly composed of ().

a.The contact potential generated by the contact between two different metal electrodes.

b.The temperature difference potential caused by the different temperatures at the two ends of a single metal.

c.Hall potential.

Correct socks to determine the answer: ab

Summary. The three important laws of thermocouples are: Standard Electrode Law:

If the thermal electromotive force produced by the thermocouple composed of each of the two conductors and the third conductor is known, the thermal electromotive force produced by the thermocouple composed of the two conductors is also known. As long as the thermal electromotive force of the thermocouple composed of various metals and pure platinum is measured, the thermal electromotive force of the thermocouple composed of various metals can be directly calculated. Fourth, the law of intermediate temperature:

The thermal electromotive force of the thermocouple at the temperature t, t0 of the two contacts is equal to the algebraic sum of the corresponding thermal electromotive forces of the thermocouple at the temperature of t, tn and tn, t0. The intermediate temperature law provides a theoretical basis for the use of compensating wires.

The three important laws of thermocouples are: Standard electrode law: If the thermal electromotive force generated by a thermocouple consisting of two conductors and a third conductor is known, then the thermal electromotive force (EMF) generated by a thermocouple composed of these two conductors is also known.

As long as the thermal electromotive force of the thermocouple composed of various sensitive metals and pure platinum is measured, the thermal electromotive force of the thermocouple composed of various metals can be directly calculated. Fourth, the law of intermediate temperature: the thermal electromotive force of the thermoelectric bridge partner at the temperature t and t0 of the two contacts is equal to the algebraic sum of the corresponding thermal electromotive force of the thermocouple at the temperature of the contact t, tn and tn and t0.

The intermediate temperature law provides a theoretical basis for the use of compensating wires.

It is useful to calculate the thermal electromotive force of the inter-phase dispersion and burial of various metals, and if the two thermoelectrode materials in the thermocouple circuit are the same, regardless of the temperature of the two contacts, the thermal electromotive force is zero.

There are 7 kinds of thermoelectric couples commonly used in industry: S, B, E, K, R, J, and T

1) Platinum rhodium 10 platinum thermocouple index 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, the temperature measurement range is 0 1600; Platinum rhodium 30 wire (platinum 70%, rhodium 30%)

Whether it is the object being measured or the object of the thermocouple itself.

Commonly used thermocouples can be divided into two categories: standard thermocouples and non-standard thermocouples. The so-called standard thermocouple refers to the thermocouple that stipulates the relationship between its thermoelectric potential and temperature, the allowable error, and has a unified standard indexing table. Non-standardized thermocouples are inferior to standardized thermocouples in terms of scope or order of magnitude, and generally do not have a unified indexing table, which is mainly used for measurement in some special occasions.

Standardized thermocouples in ChinaSince January 1, 1988, thermocouples and RTDs have been produced in accordance with IEC international standards, and seven standardized thermocouples have been designated as S, B, E, K, R, J, and T as thermocouples of unified design for China.

Theoretically, any two different conductors (or semiconductors) can be formulated into thermocouples, but as a practical temperature measuring element, the requirements for it are manifold. In order to ensure the reliability in engineering technology, as well as sufficient measurement accuracy, not all materials can form thermocouples, and the basic requirements for electrode materials for thermocouples are:

1. Within the temperature measurement range, the thermoelectric properties are stable, do not change with time, have sufficient physical and chemical stability, and are not easy to oxidize or corrode;

2. The temperature coefficient of resistance is small, the conductivity is high, and the specific heat is small;

3. The thermoelectric potential generated in temperature measurement should be large, and the relationship between thermoelectric potential and temperature is linear or nearly linear as a single value function;

4. The material has good reproducibility, high mechanical strength, simple manufacturing process and low price.

Due to the different objects to be measured, different environmental conditions, different measurement requirements, and different installation methods and measures taken for thermal resistance in production, there are many problems that need to be considered, but in principle, it can be considered from three aspects: the accuracy of temperature measurement, safety, and convenient maintenance.

A thermocouple is a temperature-sensing element and a primary instrument that directly measures temperature. UE thermocouple has a wide temperature measurement range, relatively stable performance, and the thermocouple is in direct contact with the measured object, which is not affected by the intermediate medium. Thermocouples are widely used in production processes such as chemical oil refining.

Thermocouple is a more commonly used temperature measurement method, thermocouple is divided into multiple graduation numbers, and each graduation number corresponds to a different temperature range.

When selecting the model, you can choose the corresponding temperature range, not the larger the temperature measurement range, the better.

The specific temperature range is listed for you.

I have it on my ** profile.