How the temperature sensor works

Temperature Sensor

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.

working principle

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

DIN IEC751 coefficient: A=3.9083E-3, B=-5.775E-7, C=-4.183E-12

According to the Vedic formula, the conversion formula of Rt ->t whose resistance is 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), which belongs to the positive resistivity. The relationship between resistance and temperature change is as follows: R = Ro(1 + αT) where α = 0.00392, Ro It is a 100 Ω (resistance value at 0 ° C), T is a temperature range of Celsius, so platinum is a resistive temperature detector, also known as 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 use it 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.

Curve chart

PT100/PT1000 platinum resistance RT curve chart

Folding index table

- 50 degrees 80.31 ohms

-40 degrees 84.27 ohms

-30 degrees 88.22 ohms

-20 degrees 92.16 ohms

-10 degrees 96.09 ohms

0 degrees 100.00 ohms

10 degrees 103.90 ohms

20 degrees 107.79 ohms

30 degrees 111.67 ohms

40 degrees 115.54 ohms

50 degrees 119.40 ohms

60 degrees 123.24 ohms

70 degrees 127.08 ohms

80 degrees 130.90 ohms

90 degrees 134.71 ohms

100 degrees 138.51 ohms

110 degrees 142.29 ohms

120 degrees 146.07 ohms

130 degrees 149.83 ohms

140 degrees 153.58 ohms

150 degrees 157.33 ohms

160 degrees 161.05 ohms

170 degrees 164.77 ohms

180 degrees 168.48 ohms

190 degrees 172.17 ohms

200 degrees 175.86 ohms

component

Common pt100 temperature sensing elements are ceramic components, glass components, mica components, which are processed by a complex process of platinum wire wound around a ceramic skeleton, a glass skeleton, and a mica skeleton.

Application range

High-precision temperature equipment such as Medical, motor, industrial, temperature calculation, and resistance calculation, has a wide range of applications.