Platinum-rhodium thermocouple

I. Working principle

Thermocouple is composed of two different components of the conductor (called thermocouple wire or thermal electrode) at both ends of the synthetic circuit, when the temperature of the two joint point is not the same, in the circuit will produce electromotive force, this phenomenon is called thermoelectric effect, and this electromotive force is called thermoelectric potential. Thermocouples make use of this principle to measure the temperature. One end is called the working end (also known as the measuring end) and the other is called the cold end (also known as the compensation end). The cold end is connected to a display meter or matching meter that indicates the thermoelectric potential generated by the thermocouple.

Ii.the principle structure

Thermocouple is a temperature measuring element commonly used in temperature measuring instruments. It directly measures the temperature and converts the temperature signal into thermoelectric electromotive force signal, which is converted into the temperature of the measured medium through the electrical instrument (secondary instrument). The appearance of various thermocouples is often different due to the need, but their basic structure is generally the same, usually by the hot electrode, insulation sleeve protection tube and junction box and other main parts, usually with display instruments, recording instruments and electronic regulator matching use.

Iii. Principles related features and advantages

1. Simple assembly and easy replacement;

2. Pressure spring type temperature sensor, good seismic performance;

3. High measurement accuracy;

4. Large measuring range (-200 ° C ~ 1300 ° C, -270 ° C ~ 2800 ° C in special cases);

5. Fast thermal response time;

6. High mechanical strength and good pressure resistance;

7. High temperature resistance up to 2800 degrees;

8. Long service life.

Advantages:

1. High measurement accuracy. Because of direct contact with the measured object, not affected by the medium.

2. Wide measuring range. Thermocouples in common use can be continuously measured from minus 50 degrees Celsius to 1600 degrees Celsius. Some special thermocouples can measure as low as -269 degrees Celsius (e.g., fe-Ni-Cr) and as high as 2800 degrees Celsius (e.g., tungsten and rhenium).

3. Simple structure and easy to use. A thermocouple is usually made of two different kinds of wire, and is not limited by size or beginning. It has a protective sleeve, which makes it very convenient to use.

vi.?Install

Notes for site use and installation requirements

It directly measures the temperature, and converts the temperature signal into thermoelectric electromotive force signal, and converts it into the temperature of the measured medium through the electrical instrument (secondary instrument). The installation mode of thermocouple: the main fixed mode has thread connection, flange connection and welding, its application and requirements are different, mainly according to the pressure, temperature and other parameters to determine. So what should we pay attention to when installing and using it?

1. When using the thermocouple compensation wire, the model must be matched, and the temperature of the compensation wire and the thermocouple connection end must not exceed 100℃.

2. When the thermocouple with a large time constant is used to measure or control the temperature, although the temperature fluctuation shown by the instrument is small, the fluctuation of the actual furnace temperature may be large, so a thermocouple with a small time constant should be selected.

3, according to the instrument wiring diagram of the correct wiring power, the instrument first display the thermocouple indexing number, then display the instrument range, and then measure the digital tube below the instrument display the set temperature, the digital tube above the instrument display the measured temperature.

4, thermocouple can not be installed in the measured medium rarely flow in the area, when the thermocouple measurement tube gas temperature, must make the thermocouple against the direction of flow rate installation, and fully contact with the gas.

5. In order to make sufficient heat exchange between the measuring end of thermocouple and thermal resistance and the measured medium, the position of measuring point should be selected reasonably, avoiding the valve as far as possible

6. According to the middle conductor law, in the actual thermocouple temperature measurement application, the form of hot end welding and cold end open circuit is often adopted, and the cold end is connected with the display instrument to form the temperature measurement system.