Thermocouple (also referred to as a thermoelectric temperature transducer) is the most widely spread temperature sensor (thermal element) used in measuring and transducing instruments. Temperature measurements by means of thermocouples are widely spread due to sensor’s reliability, wide operating temperature range and relatively inexpensive price.
Thermocouples are widely used due to their simplicity, easy installation and possibility of local temperature measurements. They are much more linear than the majority of other sensors, besides, their non-linear features have been thorougly studied and desribed in corresponding literature. One more advantage of thermocouples is their high responce speed and possibility of minor temperature differences control. The thermocouples are essential for high temperature measurements (up to 2200°С) in aggressive environments. The thermocouples provide high measurements precision at the level of ±0,01°С. The thermocouples generate thermal EMF in the range from microvolt up to millivolt. However, for the purpose of further processing, stable amplification level is required.
Thermocouple consists of two wires that are welded at one side. The wires are made of metals having different thermoelectrical properties. Hot junction is placed into the controlled environment and and the loose wires (cold junction) are connected to temperature controllers input.
Since the thermal EMF value depends on the temperature difference of thermocouple’s junctions, for the purpose of obtaining precise values, it is necessary to know cold junction’s temperature value (this value is to be used in the course of further calculations). Some input modifictaions enable automated compensation of the thermocouple’s cold junctions. In this case a semiconducting diode installed near the therminal bus is used as a cold junction’s temperature sensor. Thermocouple’s connection to an instrument should be implemented by means of thermocouple wires made of the material identical to that of the thermocouple. During connection of thermocouple wires it is necessary to observe polarity. In order to avoid negative impact on the measuring section it is recommended to screen the connection line between the instrument and the sensor. As a screen one can use earthed steel tube. Non-observance of the above listed recommendations may lead to high percentage of measuring error.
Thermocouples together with Digital temperature sensors ZETSENSOR form digital temperature sensors and enable cost-effective high-precision measurements.