_ instrument of thermocouple temperature measurement conditions
Thermocouple is a temperature sensing element, is a kind of an instrument, thermocouple temperature measurement directly.
Composed of two different composition material of the conductor closed loop, because material is different, different electron diffusion of electron density, stable equilibrium is produced after electric potential.
When temperature gradient is at both ends, the loop will be current, produce thermoelectric emfs, the bigger the temperature difference, the greater the current will be.
To know the temperature after the measured thermoelectric emfs.
Thermocouple is, in fact, a kind of energy converter, can convert heat into electricity.
Thermocouple technical advantages: wide thermocouple temperature measurement range and stable performance compare;
High measurement accuracy, thermocouple direct contact with the object being measured, not affected by the intermediate medium;
Thermal response time is fast, flexible thermocouple response to temperature changes;
Wide measurement range, the thermocouple
40 ~ + 1600 ℃ can be continuous temperature measurement;
Thermocouple performance is stable, good mechanical strength.
Long use life, device for lunch.
Thermocouple must be composed of two different nature but fit certain requirements of conductor (
Or a semiconductor)
Material composition loop.
Thermocouple measurement must have a temperature difference between side and reference.
The two different information conductor or semiconductor welding, A and B constitute A closed loop.
When the conductor A and B two persistent point temperature difference between 1 and 2, occurs between the electromotive force, therefore constitute the size of A current in the circuit, this kind of phenomenon called the thermoelectric effect.
Thermocouple is using this effect to work.
Thermocouple three basic laws 1, homogeneous conductor's law by the same kind of homogeneous material,
A conductor or semiconductors)
Welding on both ends of a closed loop, whatever how conductor cross section and the temperature distribution, will not produce contact potential, temperature potential phase offset, loop total potential is zero.
Visible, thermocouple must be made up of two different homogeneous conductors or semiconductors.
Jorge electrode material uneven, because temperature ladder, will produce the attached heating electric potential.
2, the law of conductor in the middle of the thermocouple loop access among conductor (
The third conductor)
, as long as the middle temperature is the same on both ends of the conductor, the introduction of the center conductor has no effect on the thermocouple loop total potential, this is the law of conductor in the middle.
Application: according to the law of middle conductor in thermocouple temperature measuring actual applications, often takes the form of hot side welding, cold end open circuit, the cold end by the wires are connected to the digital display table constitute a temperature measuring system.
Any compensation conductor connection thermocouple cold end to the digital display table read mV values, the conductor and thermocouple junction of contact potential measurement causes additional error.
According to this law, it is not the error!
3, law of intermediate temperature thermocouple loop two contact (
Temperature T, T0)
Between thermoelectric potential, equal to the thermocouple in the thermoelectric potential when temperature T, Tn and when the temperature of Tn, T0 algebra and thermoelectric potential.
Tn said the middle temperature.
Application: as the thermocouple E -
Usually non-linear relationship between T, when the cold end temperature of 0 degrees Celsius, cannot use the known loop real thermoelectric potential E (
Directly look-up table to calculate the temperature value of hot end;
Also can't use the known loop real thermoelectric potential E (
Direct look-up table to calculate the temperature value, plus the cold end temperature to determine the measured temperature value of hot end, should be carried out according to the laws of the intermediate temperature correction.
Beginners often not according to the law of middle temperature to fix!