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Pt100 is a platinum thermal resistance whose resistance changes with temperature. A 100 after PT means that it has a resistance of 100 ohms at 0 ° C and a resistance of about 138.5 ohms at 100 ° C. Due to the relationship between the temperature value of the PT100 thermal resistance and the resistance value, it is convenient to use this characteristic to develop and produce the PT100 thermal resistance temperature sensor.
How the temperature sensor works
Its working principle: When the PT100 is at 0 degrees Celsius, its resistance is 100 ohms, and its resistance will increase approximately evenly with the temperature rise. But the relationship between them is not a simple proportional relationship, but should be closer to a parabola.
The formula for calculating the resistance of platinum resistance as a function of temperature:
-200
0≤t<850°C Rt=R0(1 At Bt2) (2)
Rt is the resistance value at t ° C, and R 0 is the resistance value at 0 ° C. The A, B, and coefficient in the formula are experimentally determined. Given the standard here
DIN IEC751 coefficient: A=3.9083E-3, B=-5.775E-7, C=-4.183E-12
According to the Weida formula, the conversion formula of Rt ->t with resistance value greater than or equal to 100 ohms is obtained:
0≤t<850°C t=(sqrt((A*R0)^2-4*B*R0*(R0-Rt))-A*R0)/2/B/R0
The PT100 temperature sensor is a resistive temperature detector made of platinum (Pt). It belongs to the positive resistivity. The relationship between resistance and temperature change is as follows: R=Ro(1 αT) where α=0.00392, Ro is 100Ω (resistance at 0°C), T is Celsius
Therefore, the resistive temperature detector made of platinum is also called PT100.
1: Vo = 2.55 mA × 100 (1 0.00392 T) = 0.255 T/1000.
2: When measuring Vo, no current can be separated, otherwise the measured value will be inaccurate. Circuit analysis Because the power supply is more than the general power supply, the power supply is with noise, so we use Zener diode as the voltage regulator part, because of the role of 7.2V Zener diode, make 1K resistor and 5K variable resistor The voltage sum is 6.5V, and the adjustment of the 5K variable resistor determines the emitter (collector) current of the transistor. We must adjust the collector current to 2.55mA, so that the measurement voltage V is 0.255 as indicated by the arrow. T/1000. Subsequent non-inverting amplifiers, the input resistance is almost infinite, and at the same time amplified 10 times, making the op amp output 2.55 T / 100. 6V Zener diode role as 7.2V Zener diode, we It is used to call up 2.55V, so the output voltage V1 of the voltage follower is also 2.55V. The output of the differential amplifier is then Vo=10(V2-V1)=10(2.55 T/100-2.55)=T/10. If the current room temperature is 25°C, the output voltage is 2.5V.
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