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K-type thermocouple four laws
Dec 27, 2017

K-type thermocouple four laws

Four laws

1, the law of homogeneous conductor

Thermocouple wire from the same homogeneous material (conductor or semiconductor) to form a closed loop at both ends, no matter how the conductor cross-section and temperature distribution, will not produce contact potential, temperature potential offset, the total potential zero loop.

It can be seen that the thermocouple must consist of two different homogeneous conductors or semiconductors. If the thermal electrode material is not uniform, due to the presence of temperature ladder, will produce additional thermoelectric power.

2, the law of the middle conductor

In the thermocouple circuit access to the middle conductor (third conductor), as long as the middle conductor at both ends of the same temperature, the introduction of the middle conductor of the thermocouple circuit has no effect on the total potential, which is the middle conductor law.

Application: According to the law of the middle conductor, thermocouple in the actual temperature measurement applications, often using hot-side welding, cold end open the form of the cold junction by connecting wires and display instruments constitute a temperature measurement system.

Some people worry about using copper wire connected to the thermocouple cold junction to the meter reading mV value, in the wire and thermocouple connection generated contact potential will make the measurement of additional error. According to this law, there is no such error!

3, the middle temperature law

Thermocouple circuit two contacts (temperature T, T0) between the thermoelectric power, equal to the thermocouple at the temperature T, Tn thermoelectric power at the temperature Tn, T0 when the thermoelectric power of the sum. Tn said intermediate temperature.

Application: As the thermocouple ET usually non-linear relationship between, when the cold junction temperature is not 0 degrees Celsius, can not use the actual circuit of the known thermoelectric power E (t, t0) look-up table to obtain the hot side temperature value; Using the known circuit actual thermoelectric power E (t, t0) look-up table to obtain the temperature value, coupled with cold-side temperature to determine the hot-side measured temperature value, according to the law of the middle temperature to be amended. Beginners often do not amend the law by the middle of the temperature!

4, the reference electrode law

This law is a professional research, attention, general production, the use of links do not quite understand, simple description is: with high purity platinum wire to do the standard electrode, assuming nickel chromium - nickel chromium thermocouple positive and negative respectively, and standard Electrode pairing, their value added is equal to the value of this nickel chromium - nickel chromium.

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