pick want PT100 Platinum thermistor is a common temperature measurement tool, and its resistance value varies with temperatureIt changes with the variation of temperature and is widely used in the measurement and control of temperature parameters in industrial processesSystem. design based on PT100 The temperature sensor of platinum resistance thermometer changes the size of the platinum resistance thermometer according to the changes in the surrounding temperature, outputs the corresponding voltage signal through the circuit, and adds a preset value comparison circuit to alarm whether the current temperature exceeds the range.

keywords PT100 Platinum thermistor; bridge；NE5532 chip; Amplification circuit; comparison circuit

1 Introduction

Temperature sensors are widely used in industry, agricultural production, and scientific research

and other fields [1]To improve production efficiency, higher requirements are placed on the speed and accuracy of temperature parameter measurement. This article is designed based onThe temperature sensor of PT100 platinum thermistor has the characteristics of high accuracy, good linearity, and short response time.

2 circuit design

based on PT100 Platinum thermistor temperature sensor consists of two parts：PT100

Platinum resistance sensor and signal converter. pass PT100 Platinum resistance measurementTemperature, after NE5532 Combining chips and multiple components to achieve signal conversionConvert and amplify an analog voltage signal output; Afterwards, add a comparison circuit, Compare the current value with the set value and issue an alarm if it exceeds the limit. Design Block DiagramAs shown in the figure 1 As shown.

Figure 1

Figure 2

Compared with ordinary thermal resistors,PT100 The characteristics of platinum thermistors include: heat

Inertial measurement has a small lag; Good mechanical performance, vibration resistance, bending ability, and easy installation; Long service life. Therefore,PT100 Platinum thermistor is an ideal temperature measuring electronic component in research.

PT100 rtd RTThe curve chart is shown in the figure 2 As shown. when in 0At ℃,PT100 The resistance value is 100 ΩIts resistance will increase uniformly with the rise of temperatureGrowth, in 100At ℃, its resistance is about138.5 ΩIts resistance is related to temperatureThe change in degree is proportional, but it is not a simple proportional relationship, but rather should tend towardsApproaching a parabolic curve [2].

NE5532 It is a high-performance, low-noise dual operational amplifier（Dual operational amplifier）IntegrationCircuit. Similar to many standard operational amplifiers, but it has better noise performance, Excellent output driving capability and relatively high small signal bandwidth, power supply voltage rangeCharacteristics such as large circumference. In this article, it will be used to construct bridge circuits, amplifier circuits, andCompare circuits. apply NE5532 chip PT100 Platinum resistance temperature sensorCircuit diagram as shown 3 As shown.

Figure 3

in the figure 3 In the circuit shown, the bridge circuit is R2R3R9 and PT100Composition of resistance. To prevent excessive circuit current from causingPT100 Damaged, for the sake of protectionProtect the circuit,R2=R3=13 KΩBecause PT100 The small resistance value is 100 Ω（namely 0℃The resistance value below）In order to ATheB The voltage difference between two points is small, rootAccording to the scale table of platinum resistance thermometer, take R=96.09 Ω or 92.16 Ω That's rightAppropriate, but in reality, the most important thing is R=91 Ω The resistance is taken, soR9=91 ΩThis is beneficial for reducing errors. From the diagram, it can be seen thatATheB Two point electricityVoltage and bridge output（ATheB Two point voltage difference）They are:

among which UAThe value of varies with the temperature of the working environment.UATheUBTo amplify the input voltage of the circuit later. Utilizing by R1TheR5TheR7TheR10 andNE5532 The chip constitutes a differential amplification circuit, and the output power of this basic subtraction circuit isPressed as:

The magnification factor is:

output C Add voltage comparison after clicking Road, by R4R11 andNE5532 Chip composition. compare NE5532 Operational amplifier input terminal 5 Feet and 6 Between the feetVoltage magnitude, when UC ＞ UD When the measured temperature is greater than the set temperature, output voltage UE for 12 VAt this moment LED The light is on, indicating an alarm. Adjustable hereresistance R4 The function is to set the voltage preset value by changing R4 It can be changedD Point voltage for voltage preset;R6 It plays a role in limiting current and isolating, making the leftThe circuits on the right side are not affected by interference;C1 It plays a filtering role.

1 Test results

Measure the temperature of the circuit welded according to the designCorresponding to 30-100 ℃

The data record of the resistance value is shown in Table 1.

pass GRAPH Software, based on measured values and utilization PT100 Standard divisionThe function diagram of the table is shown in Figure 4. Among them, the red line represents the actual measurementData, blue is the standard scale, the two are more consistent（Explanation: Above isRed line, black line below).

Using the data from the graduation table for formula calculation, we obtain:

Combined type 3、4 Obtain the output voltage after circuit amplification UCWith temperatureThe relationship between degrees is:

Enter the power supply voltage here VCC=5 V，K=100，R2=R3=13 000 Ω，

R9=91Ω, then formula6 is:

Conclusion

based onPT100The temperature sensor of platinum resistance thermometer has a simple structure, low cost, and stable performance, making it an ideal temperature data collector. Combining industrial control computers in the industrial production process can achieve control functions such as temperature acquisition, heating and cooling.