Electronic Circuit of Platinum Resistance Temperature Sensor
Temperature sensor measurement systems are widely used, involving all aspects of all walks of life, and occupy an important position in various fields. Starting from reducing development costs, expanding the scope of application, and improving the stability and reliability of system operation. Design a temperature measurement system using PT100 platinum thermal resistor as the temperature signal acquisition element, EW78E58 microcontroller as the control core, and OCMJ4@8C liquid crystal display as the display device.
Voltage amplification and A/D conversion interface circuit
The voltage output by one end of the PT100 platinum thermal resistor is very small. If directly connected to the A/D converter, the conversion data will have a large deviation. Therefore, in this design, the voltage output by one end of the PT100 platinum thermal resistor is amplified 10 times and connected to the voltage follower, and then A/D conversion is performed. In this way, a better conversion effect can be obtained, as shown in Figure 2. Precision amplifier INA118 and voltage reference chip MC1403 form an amplifier circuit. VIN+ is the voltage value output by one end of the PT100 platinum thermal resistor; WIN- is the voltage value output by the reference voltage source MC1403; VOUT is the amplified output voltage value.
Choose a dual-integrating 3 (1/2)-bit MC14433 chip A/D converter (equivalent to 11-bit binary numbers). MC14433 adopts dynamic scanning BCD code output mode, that is, thousands, hundreds, tens, and units BCD codes are output at the Q0~Q4 terminals in turn. At the same time, synchronization word bit strobe signals appear at the DS1~DS4 terminals. As shown in Figure 3. MC1403 integrates a precision + 2.5 V voltage source that is divided by a potentiometer as the reference voltage for A/D conversion. The DU terminal of MC14433 is connected to the EOC terminal to select the continuous conversion mode, and each conversion result is sent to the output register. EOC is the output flag signal for the end of A/D conversion. When the microcontroller reads the A/D conversion result, it can use interrupt mode or query mode. In order to keep the microcontroller busy with other tasks, this design system uses interrupt mode. The DU terminal is connected to the EOC and then optically coupled to the INT1 terminal of the microcontroller.
Optocoupler isolation circuit
The number of characters further maximizes the application of liquid crystal display technology in single-chip microcomputer systems. The OCMJ4 @8C module is very suitable for intelligent instrumentation systems and household appliances that display a large amount of Chinese character information. Two data transmission methods can be used: 8-bit parallel interface to transmit signals and serial interface and serial transmission data. This design system adopts parallel transmission method. The microcontroller control and LCD interface circuit is shown in the figure (J91 and J11 are used to connect the LCD).
Microcontroller and LCD interface circuit diagram
Comments and analysis by the technical editor of Electronic Enthusiast Network:
The SoE system based on microcontroller and LabVIEW realizes a low-cost data acquisition system architecture. In actual development, LabVIEW shows great flexibility. The microcontroller data acquisition system in the LabVIEW environment combines the flexibility of the microcontroller for data acquisition with the powerful data analysis and processing capabilities of Lab2VIEW, and can be widely used in the field of measurement and control. This measuring system can measure not only indoor temperatures, but also temperatures in liquids, seeds, etc. In practical applications, the system operates stably and reliably, and the circuit design is simple and practical.
The voltage output by one end of the PT100 platinum thermal resistor is very small. If directly connected to the A/D converter, the conversion data will have a large deviation. Therefore, in this design, the voltage output by one end of the PT100 platinum thermal resistor is amplified 10 times and connected to the voltage follower, and then A/D conversion is performed. In this way, a better conversion effect can be obtained, as shown in Figure 2. Precision amplifier INA118 and voltage reference chip MC1403 form an amplifier circuit. VIN+ is the voltage value output by one end of the PT100 platinum thermal resistor; WIN- is the voltage value output by the reference voltage source MC1403; VOUT is the amplified output voltage value.
Choose a dual-integrating 3 (1/2)-bit MC14433 chip A/D converter (equivalent to 11-bit binary numbers). MC14433 adopts dynamic scanning BCD code output mode, that is, thousands, hundreds, tens, and units BCD codes are output at the Q0~Q4 terminals in turn. At the same time, synchronization word bit strobe signals appear at the DS1~DS4 terminals. As shown in Figure 3. MC1403 integrates a precision + 2.5 V voltage source that is divided by a potentiometer as the reference voltage for A/D conversion. The DU terminal of MC14433 is connected to the EOC terminal to select the continuous conversion mode, and each conversion result is sent to the output register. EOC is the output flag signal for the end of A/D conversion. When the microcontroller reads the A/D conversion result, it can use interrupt mode or query mode. In order to keep the microcontroller busy with other tasks, this design system uses interrupt mode. The DU terminal is connected to the EOC and then optically coupled to the INT1 terminal of the microcontroller.
The number of characters further maximizes the application of liquid crystal display technology in single-chip microcomputer systems. The OCMJ4 @8C module is very suitable for intelligent instrumentation systems and household appliances that display a large amount of Chinese character information. Two data transmission methods can be used: 8-bit parallel interface to transmit signals and serial interface and serial transmission data. This design system adopts parallel transmission method. The microcontroller control and LCD interface circuit is shown in the figure (J91 and J11 are used to connect the LCD).
Comments and analysis by the technical editor of Electronic Enthusiast Network:
The SoE system based on microcontroller and LabVIEW realizes a low-cost data acquisition system architecture. In actual development, LabVIEW shows great flexibility. The microcontroller data acquisition system in the LabVIEW environment combines the flexibility of the microcontroller for data acquisition with the powerful data analysis and processing capabilities of Lab2VIEW, and can be widely used in the field of measurement and control. This measuring system can measure not only indoor temperatures, but also temperatures in liquids, seeds, etc. In practical applications, the system operates stably and reliably, and the circuit design is simple and practical.
