Thermocouple thermometers - Thermoelectric effect temperature measurement
Definition:
A pair of conductive materials that generate electromotive force in a circuit based on the Zebeck effect. A sensitive element for temperature measurement using a pair of conductors of different materials bonded together at one end and their thermoelectric effect.
Overview:
A thermocouple is a temperature sensing element and an instrument. It directly measures temperature and converts the temperature signal into a thermoelectric electromotive force signal, which is then converted into the temperature of the measured medium through electrical instruments (secondary instruments). The basic principle of thermocouple temperature measurement is that two different materials of conductors form a closed circuit. When there is a temperature gradient at both ends, there will be current passing through the circuit. At this point, there is an electromotive force between the two ends - thermoelectric electromotive force, which is called the Seebeck effect. Two homogeneous conductors with different compositions are thermoelectric electrodes, with the working end at the higher temperature and the free end at the lower temperature. The free end is usually at a constant temperature. According to the functional relationship between thermoelectric electromotive force and temperature, a thermocouple graduation table is made; The graduation table is obtained under the condition of a free end temperature of 0 ℃, and different thermocouples have different graduation tables.
When a third metal material is connected to the thermocouple circuit, as long as the temperature of the two contacts of the material is the same, the thermoelectric potential generated by the thermocouple will remain unchanged, that is, unaffected by the connection of the third metal to the circuit. Therefore, when measuring temperature with a thermocouple, a measuring instrument can be connected, and after measuring the thermoelectric electromotive force, the temperature of the measured medium can be known. When measuring temperature, a thermocouple requires the temperature of its cold end (the measuring end is the hot end, and the end connected to the measuring circuit through a lead is called the cold end) to remain constant, so that its thermoelectric potential is proportional to the measured temperature. If the temperature of the cold end changes during measurement, it will seriously affect the accuracy of the measurement. Taking certain measures at the cold end to compensate for the impact caused by temperature changes at the cold end is called thermocouple cold end compensation. Attachment: Calculation method for thermocouple cold junction compensation: From millivolts to temperature: Measure the cold junction temperature, convert it to the corresponding millivolt value, and add it to the millivolt value of the thermocouple to calculate the temperature. From temperature to millivolts: Measure the actual temperature and cold end temperature, convert them into millivolts, subtract them to obtain millivolts, and obtain the temperature.
