The difference between thermocouple and pt100 thermal resistor

Thermocouple temperature measurement principle and materials Thermocouple temperature measurement is based on the property that the resistance value of metal conductor increases with the increase of temperature to measure temperature. Most thermal resistors are made of pure metal materials. Currently, platinum and copper are widely used. In addition, nickel, manganese and rhodium are now being used to make thermal resistors.

Thermocouple is one of the commonly used temperature detection elements in industry.

Thermocouple working principle

It is based on the Seebeck effect, that is, the two ends of two conductors of different components are connected into a loop. If the temperatures of the two connection ends are different, a physical phenomenon of thermal current is generated in the loop.

Its advantages are

High measurement accuracy. Because the thermocouple is in direct contact with the object to be measured, it is not affected by the intermediate medium.

② Wide measurement range. Commonly used thermocouples can measure continuously from -50~+1600℃. Some special thermocouples can measure as low as -269℃ (such as gold, iron, nickel and chromium) and as high as +2800℃ (such as tungsten-rhenium).

③ Simple structure and easy to use. Thermocouples are usually composed of two different metal wires, and are not limited by size and opening. They are protected by a protective sleeve and are very convenient to use.

Types and structures of thermocouples

(1) Types of thermocouples

Common thermocouples can be divided into two categories: standard thermocouples and non-standard thermocouples.

The so-called standard thermocouples refer to thermocouples whose standards specify the relationship between thermoelectric potential and temperature, allowable error, and have a unified standard scale. They have matching display instruments for selection. Non-standard thermocouples are inferior to standardized thermocouples in terms of use range or order of magnitude, and generally do not have a unified scale. They are mainly used for measurements in certain special occasions. Standardized thermocouples Since January 1, 1988, all thermocouples and thermal resistors in my country have been produced in accordance with IEC international standards, and seven standardized thermocouples, S, B, E, K, R, J, and T, have been designated as my country's unified design thermocouples. The difference between thermocouples and PT100 thermal resistors

PT100 thermal resistors are a commonly used temperature detector in medium and low temperature zones.

Its main features

are high measurement accuracy and stable performance. Among them, the measurement accuracy of platinum thermal resistors is very high. It is not only widely used in industrial temperature measurement, but also made into a standard reference instrument.

Types of thermal resistors

1) Ordinary thermal resistors From the temperature measurement principle of thermal resistors, it can be seen that the change of the measured temperature is directly measured by the change of the resistance value of the thermal resistor. Therefore, the change of the resistance of various wires such as the lead wire of the thermal resistor body will affect the temperature measurement.

2) Armored thermal resistors are solid bodies composed of temperature sensing elements (resistance bodies), lead wires, insulating materials, and stainless steel sleeves. Its outer diameter is generally φ2-φ8mm, and the smallest can reach φ0.25mm. Compared with ordinary thermal resistors, it has the following advantages: ① Small size, no air gap inside, good thermal inertia, and small measurement value; ② Good mechanical properties, vibration resistance, and impact resistance; ③ Can be bent, easy to install ④ Long service life.

3) End face thermal resistors The end face thermal resistor temperature sensing element is wound with specially treated resistance wire and is close to the end face of the thermometer. Compared with general axial thermal resistors, it can more accurately and quickly reflect the actual temperature of the measured end face, and is suitable for measuring the end face temperature of bearings and other parts.

4) Flameproof thermal resistors Flameproof thermal resistors use a special structure of the junction box to confine the explosion of the explosive mixed gas inside its shell due to the influence of sparks or arcs to the junction box, and the production site will not cause an explosion. Flameproof thermal resistors can be used for temperature measurement in explosion-hazardous places in the BLA-B3C level area. Pt100: used for thermal resistors, thermocouples, series temperature instruments, temperature transmitters, pressure differential pressure transmitters, hot runner heaters, compensation cables, control cables, etc. Cu50: used for thermal resistors, thermal resistor thermometers, thermal resistor calibrators, thermal resistor simulators-copper thermal resistor simulators, copper thermal resistors, armored thermal resistors, etc. Pt100 and Cu50 measure different temperatures. Pt100 measures the high temperature point, and Cu50 measures the low temperature point.