The error in measuring temperature with thermocouples with any instruments is related several factors that combine together to affect the overall accuracy of the measurement: 1.Thermocople wire error:this is the error resulting from the fact that a given sample of bare thermocouple wire will not exactly meet the temperature versus millivolt relationship given the standard tables. The most accurate designation is for Type T thermocouple wire. The errors allowed for T type over the range -40 to 130℃ are 1.0 for standard wire and 0.5℃ for speical limits of error wire. 2.Reference junction error: this is the error in determing the temperature of the reference junction. Sometimes called “cold junction”. 3.Voltage measurement error: this is error in the measurement of the small voltage produced by the temperature difference between the measuing junction and the reference junction. 4.Linearization error: the temperature vs. millivolt relationship for thermocouples is inherently non-linerar. The accuracy of the conversion from voltage to temperature depends on the method that is used to make this conversation. Most commonly there is a fit to standard polynomials or interpolation within the table values. Both of these methods are subjection to some degree of error. SICC group has 20-year manufacturing experience in thermocouple wires, mineral insulated cable, thermocouple and RTD probes,get more details from us quickly.

Thermocouple compensation wireshave been widely used in thermocouple temperature measurement.Understanding the principle, function, method of action and precautions of the thermocouple compensation wire,we can give full play to the role of the thermocouple compensation wire, otherwise it will be counterproductive. In industrial production, although thermocouple has been widely used in temperature measurement and control as temperature sensors, people are familiar with this, but if you do not pay attention to the correct use method, it will cause great deviations in temperature measurement and temperature control. Even directly causing economic losses, should be taken seriously. 1. Principle A circuit composed of two different metal conductors A and B connected together is called a thermocouple. If the junction temperature T1 and T2 are different, an electric potential will be generated in the circuit, usually called thermoelectric potential. When the materials of A and B are constant, the thermoelectric potential depends on the temperature difference between T1 and T2. When the materials of A and B are constant, the thermoelectric potential depends on the temperature difference between T1 and T2. According to the law of thermocouple intermediate conductors, as long as the temperature of junctions J2 and J3 in the right figure are the same, both are T2, and both of connecting wires are the same homogeneous material, and the right and left figures are equivalent. 2. Compensation wire After the thermocouple is installed in the field, it must be connected to the instrument to measure or control the temperature. Since thermocouple is always used some distance away from the measuring or controlling instrument, the temperature at the thermocouple terminal is not the same as the temperature at the input of the instrument. Generally speaking, a reference junction temperature compensation problem is needed, and the compensation wire does not compensate the reference junction, it only extends the reference junction to a specific position for processing, so the compensation wire is also called the thermocouple extension wire. There are two kinds of materials for making compensation wires. One is that within a specific temperature range, the thermoelectric potential generated by the compensation wire is similar to that of the thermocouple to be used, which is called compensation wire; the other is made of thermocouple material, known as extension wires. Such extended wires are obviously not possible for noble metal thermocouple. The compensation wire is an important part of the thermocouple measurement, so the corresponding model must be selected correctly and reasonably, and the compensation wires of different types cannot be mixed. 3. Common errors in use (1) The positive and negative poles of the thermocouple compensation wire and the thermocouple are reversed If the posit...

The principle of thermocouple is base on the binding ability of metal atoms(ions) to free electrons in metals related to temperature, different kinds of metal atoms(ions) have different binding abilities to free electrons. The metal on both sides of the fusion interface after two kinds of metals are welded together has different binding ability to free electrons, the large one is positively charged and the other side is negatively charged. There is electromotive force (EMF) difference between the two sides of metals that be changed with the temperature, the value of EMF is small but can be accurately measured. 1.The practical use of thermocouple is not as simple as the above principle, sometimes the thermocouple need to be extended, the materials of thermocouple extension wire is not necessarily the same as the thermocouple metal material, as long as the temperature of the positive and negative joint is the same, it has no effect on temperature measurement. 2.Since the instrument measure the electromotive force, there is no current in the thermocouple wire in principle. 3.Since the EMF is very small, it is susceptible to various electromagnetic interferences in many cases, so be attention to this. 4.In some case, it is necessary to measure the temperature of the charged object, such as the temperature of wire joint, power terminal block, There are many instruments that can directly measure the temperature, but the thermocouple alloy wire has a high voltage that could be dangerous to the personnel, therefore the wires from the instrument to measured object need to be insulated from the personnel during the measurement, it must be powered off when adjust the contact points of the instrument and the measuring points. Get more information from www.super-instrument.com.

With the rapid development of science and technology, the application range oftemperature sensors is becoming wider and wider, and they can be seen everywhere in daily life, which brings great convenience to people's life and industrial production. Temperature sensors organically combine semiconductor-related material and circuit properties to achieve the purpose of accurately measuring the ambient temperature. It can efficiently measure the temperature of various objects and prevent the phenomenon of short circuit of wires due to overheating of electrical appliances. 1. Sensor 1.1. Definition & Purpose A temperature sensor is defined as a sensor that senses the temperature of an object or environment and converts it into usable output information. Usually, temperature sensors are made to combine the resistance value of the NTC with the change in temperature and output signals, effectively and successfully converting physical quantities into electrical quantities, so as to accurately measure the temperature as a device. Temperature sensors can measure and control the temperature of certain objects, but also to determine the wind speed, flow rate, measurement of temperature, microwave power and ultraviolet, infrared light, not only that, temperature sensors are also used in the same time in refrigerators, TVs, water heaters, air conditioners, computer monitors, equipment in the kitchen, automobiles and many other areas. Nowadays, temperature sensors are used in a wide range of products to prevent short circuits in electrical wiring. This is the reason why temperature sensors are so important to us. 1.2. Classification At present, the commonly used temperature sensors are platinum resistance temperature sensors, PN junction temperature sensors, integrated temperature sensors, etc. According to the needs of the sensor and the environment to choose different temperature sensors. Platinum resistance temperature sensors are common sensors whose function derives from the nature of the platinum resistance. A metal conductor will fluctuate in resistance as a result of temperature changes. The principle of platinum resistance temperature sensor is to detect the ambient temperature by detecting the change of platinum resistance. If a metal conductor is used to prepare the temperature sensor, it is required to have high resistivity, low heat capacity and fast reaction speed. This type of metal such as iron, nickel, platinum, copper, etc.. However, due to the poor stability of iron and nickel, it is difficult to purify, copper and platinum have better performance. The properties of platinum are more suitable for the environment faced by temperature sensors. Therefore, platinum resistors are very common for the preparation of temperature sensors. In 0°C ~ 630.74°C mapping relationship is RT=R0 (1 + AT + BT2), in -200°C ~ 0°C mapping relationship is RT=R0 (1+ AT + BT2 + CT3). The principle of the PN junction temp...

Thermocouple wires must be correctly selected according to the type of the thermocouple as well as the operating environment. For example, we should choose the corresponding K-type thermocouple wire for K-type thermocouple and choose appropriate operating temperature range based on the operating environment. Normally, the operating temperature of K is between -20 and 100℃, the wide range is -25 ~ 200℃. The connection method Making the two thermocouple connection points as close as possible, and keeping the temperature of the two connection points as close as possible. The temperature should be consistent with the connection point of the instrument terminal. At the spots where the fan is located in the instrument cabinet, the connection point should not be blew by the fan. Length for use Since the thermocouple signal is at very low microvolt level, if it’s long distance, the signal attenuation and the interference of strong electricity in the environment could be mixed together. This is enough to cause the thermocouple signal distortion, resulting in inaccuracy of measurement and control of the temperature, or even temperature fluctuations when it’s serious. According to our experience, it is usually better to limit the length of the thermocouple compensating wire within 15 meters. When it’s over 15 meters, we recommend to use temperature transmitter for signal transmission. The temperature transmitter converts the electric potential value corresponding to the temperature into DC current DC4-20mA for transmission, with strong anti-interference ability. Method of wiring Thermocouple compensating wires must be wired away from power lines and any interference sources. When crossing is unavoidable, adopt the cross-laying method instead of the parallel laying method.   Shielded compensating wires In order to improve the anti-interference performance of thermocouple connection wires, we can use the shielded compensating wire which is more effective in the environment with strong interference. Make sure the shielding layer is strictly grounded, or the shielding layer will not shield the signal interference but actually enhance it.

The accurate and standardized application of sensors is the key to ensuring the normal operation of measurement and control equipment and realizing process technology in industrial production. Equipment operation failures and production accidents caused by improper configuration and use of temperature measurement sensors and measurement control instruments on the industrial heating furnace operation site. These failures and accidents make the temperature control of the thermometer inaccurate, which will affect the process of thermal processing production and work efficiency, resulting in a reduction in product quality. In severe cases, the product batch will be unqualified, and even cause damage to the electric furnace equipment, resulting in shutdown of the electric furnace &damage accident. Therefore, in the industrial heating production site, it is necessary to ensure that the use and supporting of temperature sensors, devices and instruments are standardized.Thermocouple is a sensor device for the temperature display and control system of an electric furnace for industrial heating. 1. Compensation wire and thermocouple mismatch use The temperature indication above 1000℃ in the high temperature zone in the thermal processing workshop is too high. When the temperature is 800℃and below, the temperature display value is also too large. 1.1. Treatment method and cause analysis (1) Method The wrong selection of compensation wire matching leads to inaccurate temperature measurement. Replace the corresponding compensation wire, and the fault is eliminated. (2) Cause When the instrument was installed on site, the matching relationship between the compensation wire and the thermocouple was ignored, resulting in failure. The principle of thermocouple temperature measurement is based on the constant temperature of the cold junction. Therefore, the negative electrode of the thermocouple should be set in an area with constant temperature at the installation site, and then achieve the purpose of accurate measurement through a certain temperature compensation; this type of temperature compensation is cold junction compensation. It should be noted that the function of the compensation wire is not to compensate the potential of the cold junction: in order to keep the temperature of the cold junction of the thermocouple temperature measuring electrode constant, the electrode must be extended, but the electrodes of the thermocouple are all precious metals.Therefore, the usual practice is to extend the cold end of the thermoelectric electrode with a metal wire with similar thermoelectric properties to the thermoelectric electrode material at room temperature (0~100℃). To the area away from the heat source and the temperature is stable, the wire of this material is called an extension wire or a compensation wire. Obviously, the function of the compensation wire is to "compensate for the lack of length of the thermode". Accord...

Thermocouple wires must be correctly selected according to the type of the thermocouple as well as the operating environment. For example, we should choose the corresponding K-type thermocouple wire for K-type thermocouple and choose appropriate operating temperature range based on the operating environment. Normally, the operating temperature of K is between -20 and 100℃, the wide range is -25 ~ 200℃. The connection method Making the two thermocouple connection points as close as possible, and keeping the temperature of the two connection points as close as possible. The temperature should be consistent with the connection point of the instrument terminal. At the spots where the fan is located in the instrument cabinet, the connection point should not be blew by the fan. Length for use Since the thermocouple signal is at very low microvolt level, if it’s long distance, the signal attenuation and the interference of strong electricity in the environment could be mixed together. This is enough to cause the thermocouple signal distortion, resulting in inaccuracy of measurement and control of the temperature, or even temperature fluctuations when it’s serious. According to our experience, it is usually better to limit the length of the thermocouple compensating wire within 15 meters. When it’s over 15 meters, we recommend to use temperature transmitter for signal transmission. The temperature transmitter converts the electric potential value corresponding to the temperature into DC current DC4-20mA for transmission, with strong anti-interference ability. Method of wiring Thermocouple compensating wires must be wired away from power lines and any interference sources. When crossing is unavoidable, adopt the cross-laying method instead of the parallel laying method.   Shielded compensating wires In order to improve the anti-interference performance of thermocouple connection wires, we can use the shielded compensating wire which is more effective in the environment with strong interference. Make sure the shielding layer is strictly grounded, or the shielding layer will not shield the signal interference but actually enhance it.

1.Use other types of wires instead of compensation thermocouple wires According to the operation principle of thermocouple temperature measurement, the thermoelectric potential of the thermocouple circuit is related to the measured temperature and the temperature of the thermocouple reference end. In the industrial site, the temperature of the thermocouple reference end is unstable and will be influenced by its surrounding environment. With temperature fluctuation ofthe reference end, the compensating wire is used to extend the reference end to an environment with stable temperature or simply somewhere away from the heat source to compensate the deviation caused by temperature changeat the reference end.Other types of wires can transmit the mV signal value generated by thermocouple temperature measurement, but can not compensate the temperature of the thermocouple reference end, which might result in inaccurate temperature compensation of thermocouple temperature measurement system. Correct method:For thermocouple signal transmission, we must use the matching type of thermocouple compensating wires with the thermocouple , it is prohibited to replace the compensating wire with a normal electric wire. 2.The insulation layer of the thermocouple compensating wire is damaged. While connecting the thermocouple, there might be certain degree of wear on the insulation layer at the outlet of the thermocouple junction box or at other parts of the compensating wire. As a result, the temperature display value on the display instrument or in the DCS system is generally smaller than usual. Correct method:Make sure to fix the insulation layer after finding damaged parts on the thermocouple compensating wire, and restore the normal display value of the control instrument or the paperless temperature recorder. 3.The measurement error occurs when the positive and negative polarity of the thermocouple compensating wire is connected reversely. The thermocouple as well as the thermocouple compensating wire both have positive and negative polarity.When the compensating wire is inversely connected, the display value on the paperless temperature recording instrument changes greatly as follows: A. After inversely connecting the polarity of the compensating wire, when the temperature at the junction of the thermocouple and the compensating wire is higher than the temperature in the control room, the temperatureshowedon the instrument will be lower than the actual measured temperature. B. After inversely connecting the polarity of the compensating wires, when the temperature at the junction of the thermocouple and the compensating wire is lower than the temperature in the control room, the temperatureshowedon the instrument will be higher than the actual measured temperature. C. After inversely connecting the polarity of the compensating wires, when the temperature at the junction of the thermocouple and the compensating wire is the same as the temperature in the control r...