Thermocouple and thermal resistance belong to the contact temperature measurement in the temperature measurement, although the same function is the measurement of the temperature of the object, but their principle and characteristics are not the same.
Thermocouple is the most widely used in temperature measurement of temperature, his main feature is a wide temperature range, performance is relatively stable, and has the advantages of simple structure, good dynamic response, better able to remote 4-20mA, convenient automatic control and centralized control. Thermocouple temperature measurement principle is based on the thermoelectric effect. The two different conductor or semiconductor are connected to form a closed loop, when the two junction temperature and loop will produce heat potential, this phenomenon called thermoelectric effect, also known as the Seebeck effect. The thermoelectric power generated in the closed loop is composed of two potential potential and the contact potential. The potential temperature is due to different temperatures of the two ends of the same conductor potential, different conductor with different electron density, so their potential is not the same and contact potential, as the name implies, is refers to two different conductor contact, because of their different electron density so produced certain electron diffusion, when they reach a certain balance after the formation of potential, contact potential depends on two different conductor material properties as well as their point of contact temperature. With a standard specification, the application of thermocouple and the thermocouple is divided into eight different indexing, respectively, B, R, s, K, N, e, J and T, measure the temperature in the lowest measurable minus 270 DEG C, up to a maximum of 180 DEG C, where B, R, s is a platinum series of thermocouples, due to the precious metals of platinum, so they were also called noble metal thermocouple and the rest of the several known as cheap metal thermocouples. There are two kinds of thermocouple structure, common type and armoured type. Ordinary thermocouple general by the hot electrode, insulating tube, protective sleeve and a terminal box and other components, and type armoured thermocouple is the thermocouple wire, insulation material and a metal protective casing are assembled, after stretching processing of a solid combination. But the electrical signal of thermocouple but requires a special wire to wire transfer, we call this compensation wire. The different needs of different thermocouple compensation wire, its main function is to make the connection with the thermocouple, thermocouple reference junction away from the power supply, so that the reference end temperature stability. Compensating conductor is divided for compensation and extended two, prolong the chemical composition of the wires and the thermocouple compensation is the same, but in practice and prolong type wire and metal instead of thermocouple made of the same material. In general, the thermocouple and have the same electron density of wires instead. The thermocouple compensation wire and wire is generally very clear, thermocouple compensation wire anode connection of the red line, and is connected to the rest of the color cathode. The general material compensation lead most of the copper nickel alloy.
The thermal resistance is not only widely used in industrial measurement, and is made of standard reference instrument. But because of his temperature range that his application is subject to certain restrictions, the measuring principle of thermal resistance is the resistance of the conductor or semiconductor with the change of temperature based on. The advantages are many can also be far EasTone telecommunications number, high sensitivity, strong stability, interchangeability and accuracy are quite good, but need the excitation power supply, not capable of measuring the instantaneous temperature changes. Industrial thermal resistance by Pt100, Pt10, Cu50, Cu100, platinum thermal resistance temperature range of minus 200-800 degrees Celsius, copper thermal resistance of minus 40 to 140 DEG C. Thermal resistance and thermocouple as the distinction between types, but he did not need the compensation wire, but also cheaper than thermocouple.
A lot of installation form of platinum thermal resistance, a fixed screw, screw fixed flange installation activities, activities, installation flange, a movable pipe joint installation, straight pipe joint installation etc..
Of thermal resistance and thermocouple choose the biggest difference is the temperature range of choice, the heat resistance is low temperature measurements of the temperature sensor, the general temperature measurement in -200~800 DEG C, and thermocouple is measurement temperature of the temperature sensor, the general temperature measurement in 400 to 1800 DEG C, the choice if the temperature measurement in about 200 DEG C should choose the thermal resistance measurement, if the temperature measurement at 600 C should choose k type thermocouple, if temperature measurement in 1200 to 1600 DEG C should select s type or B type thermocouple.
Compared with the thermal resistance and thermocouple has the following characteristics:
1, the same temperature output signal is large, easy to measure.
2, must use an external power supply measuring resistance.
3, the thermal resistance temperature size is larger, and the working end of thermocouple is very small solder joints, and thermal resistance thermometric reaction speed of the specific heat of galvanic slow;
The thermal resistance thermocouple as the upper limit of 4, similar material made of high.
The difference between thermocouple and thermal resistance:
First, the nature of the signal and thermal resistance is the resistance, temperature changes, the resistance produces a positive or negative resistance changes; the thermocouple is induction voltage changes, he will change with the temperature change. Although it is a contact type temperature measurement instrument, but their range of temperature is different, the thermocouples used in high temperature environments, such as platinum and rhodium 30--- platinum and rhodium 6 (type b) measurement range for 300 degrees ~~1600, short-term can be measured 1800 degrees. S 20~~1300 (measurement of a short 1600), K measurement of a 50~~1000, a 50~~600.XK short 1200) (800), E 40~~800 (900). There are J type, T type etc.. This kind of instrument is generally used in more than 500 degrees high temperature, low temperature zone of output thermal potential, when the potential hours, against interference measures and secondary table and demanding, or inaccurate measurement and in the lower temperature region, changes in the cold end temperature and environmental temperature changes caused by the relative error is very prominent, is not easy to get the full compensation. At this time in the low temperature, the general use of thermal resistance temperature range for a 200~~500, even can be measured with the lower temperature (such as carbon resistor can be measuring temperature to around 1K). Now normal use PT100 platinum thermal resistance, (there is also a resistance PT50, 100 and 50 representatives of thermal resistance at 0 degrees. In the old division No. BA1 and Ba2, BA1 in zero resistance is 46 ohm, in industry is also useful for copper resistance, indexing, cu100 and CU50, but smaller temperature range, between the 50~~150, in some special occasions, also resistance indium, manganese resistance).
Second, in the work of judgment
There are positive and negative, thermocouple compensation wire is divided into positive and negative, first ensure that the connection configuration in the operation. Common short circuit, open circuit, poor contact (with a table can be used to determine the million) and deterioration (according to the surface color to identify). Check, thermocouple and the second table apart, tools for short circuit on the secondary table compensation line, indicator at room temperature and then a short circuited thermocouple terminals, table designator thermocouples where the ambient temperature, the compensation line (not a fault), and then table MV archives generally immeasurable thermocouple thermoelectric potential (such as normal, please check the process).
Thermal resistance of short circuit and open circuit with a multimeter can be judged, in operation, suspected short, as long as the end resistance demolition of a thread see display instrument, such as to maximum, short circuit of thermal resistance of return to zero, shorted wire to ensure normal configuration and connection, the table values show low or instability, protecting tube possibilities influent the display shows the minimum short-circuit maximum thermal blocking the road.
Third, from materials, the thermal resistance is a kind of metal materials, metal materials with temperature sensitive to changes in the, thermocouple is double metal materials, both two different metals, due to changes in temperature, at both ends of the two different metal wire potential difference.
Fourth, two sensor detects the temperature range is not the same, thermal resistance is generally detected 0-150 degrees temperature range (of course, detecting negative temperature), and the thermocouple detection 0-1000 temperature range (or even higher) so, the former is the low temperature detection, which is high temperature detection
.