Thermal resistance RTD element standard
On the resistance temperature detector or platinum resistance, the resistance of a metal changes the working principle of the principle thermometer in a significant and repeatable way when the temperature changes. The resistance is inversely proportional to the cross-sectional area and directly proportional to the length.
Platinum is the most widely used metal for resistance temperature detection due to the following characteristics:
1. Chemical inertness
2. The temperature coefficient of resistance is large enough to easily measure the change of resistance with temperature
3. Manufacturing metal with almost no strain (because the resistance will not change sharply with the strain)
4. The relationship between resistance and temperature is almost linear
Each resistance temperature relationship of RTD temperature sensor is defined by a term called "alpha". "Alpha" is the slope of the resistance between 0 ° C and 100 ° C. This is also known as the resistance temperature coefficient, the most common being 0.00385 Ω/Ω/° C.
Other types of RTD temperature sensors manufactured include copper, nickel, and nickel alloys.
The resistance of a single RTD temperature sensor bulb (100 Ω, 200 Ω, etc.) depends on the amount of metal between terminals and the configuration of components.
When ordering RTD temperature sensors, alpha and resistance values (i.e. Ro) at 0 ° C must be specified to match the measuring instrument used with the RTD temperature sensor.
RTD temperature sensor standards must also be specified. There are several standards for RTD temperature sensors developed by various organizations. These specifications are different, and the readout instrument must be adjusted to the specific standard of the RTD used with the device.
If one standard is connected to another standard instrument, the difference of alpha value of these standards will cause RTD measurement error.
The following figure shows some common RTD component standards.
RTD temperature sensor element type
