Thermal resistance thermometer is a sensor that accurately measures temperature based on the principle that the resistance value of a conductor or semiconductor material changes systematically with temperature. Its core lies in utilizing the "resistance temperature characteristics" of materials to indirectly and accurately determine temperature values through precise measurement of the electrical parameter of resistance.
1、 Core Physics Principle: Temperature Effect of Resistance
The cornerstone of its work is the inherent relationship between the resistivity of a substance and temperature. For high-purity metal conductors such as platinum and copper, within their effective temperature measurement range, there is a good and reproducible positive correlation between resistivity and temperature. That is, as the temperature increases, atomic thermal motion intensifies, and the scattering effect on directionally moving electrons increases, resulting in a regular increase in resistance value. This change relationship is deterministic and calibratable, making it possible to estimate temperature by measuring resistance. In order to ensure international uniformity and accuracy, relevant standards have strict regulations on the resistance temperature relationship of specific materials, especially platinum.
2、 Temperature measurement mechanism and signal conversion chain
The entire temperature measurement process of a thermal resistor is a precise signal conversion and processing chain, with the following specific steps:
Temperature sensing and primary conversion: The temperature sensing element (usually an extremely thin metal wire wound or deposited on an insulating skeleton) exchanges heat with the measured medium to achieve thermal equilibrium. The change in temperature (Δ T) directly and linearly triggers a corresponding and precise change in the resistance value of the temperature sensing element itself (Δ R). This step completes the most critical primary conversion from "thermal quantity" (temperature) to "electrical quantity" (resistance).
Precision resistance measurement: How to accurately measure this small resistance change is the core to ensure accuracy. Usually, Wheatstone bridge or more precise measurement circuits are used. Using a thermistor as an arm of the measurement bridge, when its resistance value changes with temperature, it will disrupt the balance of the bridge and output a millivolt level voltage signal proportional to the change in resistance. In order to overcome measurement errors caused by wire resistance during long-distance transmission, the three wire or four wire connection method is commonly used to effectively compensate or eliminate the influence of lead resistance in circuit design.
Signal processing and linearization: The weak signal output by the bridge needs to be amplified by an instrumentation amplifier. Subsequently, due to the fact that the actual resistance temperature relationship curve is not an ideal straight line, the built-in microprocessor or dedicated circuit will linearize it to ensure that the output signal maintains a highly consistent linear relationship with the temperature value throughout the entire temperature measurement range.
Standard signal output: After amplification, linearization, and temperature compensation, the signal is finally converted into an industrial standard 4-20mA analog current signal or digital signal, which can be transmitted to display instruments, recorders, or control systems remotely and anti-interference, completing the monitoring and control of the entire temperature.
In summary, the thermal resistance thermometer accurately converts temperature into resistance value through its temperature sensing element, and then through precise electronic measurement and processing circuits, converts this resistance value into a standardized signal that can be remotely transmitted and controlled, thereby achieving high-precision and high stability temperature measurement. It is widely used in industrial process control and scientific experiments.