PT100 temperature collector with Modbus485 communication
阅读说明：本技术 带Modbus485通信的PT100的温度采集器 (PT100 temperature collector with Modbus485 communication ) 是由 童华光 陈超 曹辉辉 于 2020-07-23 设计创作，主要内容包括：本发明公开了一种带Modbus485通信的PT100的温度采集器,属于温度采集器技术领域,解决了温度数据采集可靠性和数据传输可靠性问题,其技术方案要点是包括三线制的铂热电阻和直流电压转换模块,其特征是,还包括改良电桥模块电路、温度信号放大模块电路、模数转换电路、MCU模块电路、485通信模块电路；铂热电阻与改良电桥模块电路相连接,改良电桥模块电路与温度信号放大模块电路相连,温度信号放大模块电路与模数转换电路相连,模数转换电路与所述MCU模块相连接,所述MCU模块和485通信模块电路相连接,直流电压转换模块为电路元器件提供合适工作电压,达到了提高温度采集,数据传输的可靠度和精确度效果。(The invention discloses a PT100 temperature collector with Modbus485 communication, which belongs to the technical field of temperature collectors and solves the problems of temperature data acquisition reliability and data transmission reliability, and the technical scheme is characterized by comprising a three-wire platinum thermistor and a direct-current voltage conversion module, and further comprising an improved bridge module circuit, a temperature signal amplification module circuit, an analog-to-digital conversion circuit, an MCU module circuit and a 485 communication module circuit; the platinum thermal resistor is connected with the improved bridge module circuit, the improved bridge module circuit is connected with the temperature signal amplification module circuit, the temperature signal amplification module circuit is connected with the analog-to-digital conversion circuit, the analog-to-digital conversion circuit is connected with the MCU module, the MCU module is connected with the 485 communication module circuit, and the direct-current voltage conversion module provides proper working voltage for circuit components, so that the effects of improving the temperature acquisition and the reliability and accuracy of data transmission are achieved.)
1. A PT100 temperature collector with Modbus485 communication comprises a three-wire platinum thermal resistor (100) and a direct-current voltage conversion module (200), and is characterized by further comprising an improved bridge module circuit (300), a temperature signal amplification module circuit (400), an analog-to-digital conversion circuit (500), an MCU module circuit (600) and a 485 communication module circuit (700);
the platinum thermal resistor (100) is connected with the improved bridge module circuit (300), the improved bridge module circuit (300) is connected with the temperature signal amplification module circuit (400), the temperature signal amplification module circuit (400) is connected with the analog-to-digital conversion circuit (500), the analog-to-digital conversion circuit (500) is connected with the MCU module, the MCU module is connected with the 485 communication module circuit (700), and the direct-current voltage conversion module (200) provides proper working voltage for circuit components.
2. The temperature collector of a PT100 with Modbus485 communication of claim 1, wherein: the first pin of the three-wire platinum thermal resistor (100) is connected with an analog ground end through a resistor, and the improved bridge module circuit (300) comprises a resistor R5, a resistor R2, a resistor R6, a resistor R3, a capacitor C2 and a capacitor C1;
a second pin of the platinum thermal resistor (100) is connected with one ends of a capacitor C2 and a resistor R5, the other end of the capacitor C2 is connected with an analog ground end, the other end of the resistor R5 is connected with one end of a resistor R10 and one end of a resistor R2, the other end of the resistor R4 is connected with a first voltage source, and the other end of the resistor R2 is used for outputting a first signal;
the second pin of the platinum thermal resistor (100) is connected with one ends of a resistor R6, a capacitor C1 and a resistor R3, the other end of the resistor R6 is connected with a first voltage source, the other end of the capacitor C1 is connected with an analog ground end, and the other end of the resistor R3 serves as a second signal output end.
3. The temperature collector of a PT100 with Modbus485 communication of claim 2, wherein: the temperature signal amplification module circuit (400) comprises a chip U4, a first signal output end and a second signal output end are respectively connected with the input end of the chip U4, and a matched peripheral circuit of the chip U4 is provided with an amplified signal output end.
4. The temperature collector of a PT100 with Modbus485 communication of claim 1, wherein: the analog-to-digital conversion circuit (500) comprises a chip U5 with the model of MCP3202, the chip U5 is connected with the amplified signal output end and collects temperature analog signals, the digital signal output end of the chip U5 outputs temperature digital signals, and the temperature digital signals are provided for the MCU module circuit (600).
5. The temperature collector of a PT100 with Modbus485 communication of claim 1, wherein: the MCU module circuit (600) is a chip minimum system circuit taking a chip U7 with the model of STM32F103 as a core.
6. The temperature collector of a PT100 with Modbus485 communication of claim 1, wherein: the 485 communication module circuit (700) comprises a chip U3, a transient voltage suppressor D2, a transient voltage suppressor D3, a resistor R10, a resistor R11, a resistor R12 and a resistor R13;
the model of the chip U3 is SP3485E, the chip U3 is in communication connection with the MCU module circuit (600), a seventh pin of the chip U3 is connected with a cathode of the transient voltage suppressor D2, one end of a resistor R10 and one end of a resistor R12, the cathode of the transient voltage suppressor D2 is grounded, the other end of the resistor R10 is grounded, and the other end of the resistor R12 is one end of a communication interface;
the sixth pin of the chip U3 is connected to the cathode of the transient voltage suppressor D3, one end of the resistor R11, and one end of the resistor R13, the anode of the transient voltage suppressor D3 is grounded, the other end of the resistor R11 is connected to the second voltage source, and the other end of the resistor R13 is the other end of the communication interface.
7. The temperature collector of a PT100 with Modbus485 communication of claim 6, wherein: the second voltage source is the power supply voltage of the chip U3, the resistances of the resistor R10 and the resistor R11 are equal, and the resistances of the resistor R12 and the resistor R13 are equal.
8. The temperature collector of a PT100 with Modbus485 communication of claim 2, wherein: the capacitance value of the capacitor C2 is equal to that of the capacitor C1, the resistance values of the resistor R6 are equal to that of the resistor R4, and the resistance values of the resistor R2 are equal to that of the resistor R3.
9. The temperature collector of a PT100 with Modbus485 communication of claim 2, wherein: the direct current voltage conversion module (200) also converts the 3.3V voltage into 2.5V reference voltage for output through the reference voltage source circuit (800).
10. The temperature collector of a PT100 with Modbus485 communication of claim 1, wherein: the analog ground terminal on the analog-to-digital conversion circuit (500) is connected with the ground terminal through an inductor, or a spiral lead, or a zero ohm resistor.
Technical Field
The invention relates to the field of temperature collectors, in particular to a PT100 temperature collector with Modbus485 communication.
Background
In doing some projects, some modules are used, which are often 485 interfaces, and 485 is also a common communication method in industry, and RS-485 is selected by serial connection when establishing a distributed device network connected to a PC, other data collection controllers, HMI, or other operations in industrial applications. It is known that data transmission of serial port communication is 0 and 1, but in single bus, I2C, UART,
PT100 is a platinum thermistor, abbreviated: the resistance of the PT100 platinum resistor changes along with the change of temperature. A post-PT value of 100 means that it has a resistance of 100 ohms at 0 c and a resistance of about 138.5 ohms at 100 c. The method has wide application range in editing high-precision temperature equipment such as medical treatment, motors, industry, temperature calculation, satellites, meteorology, resistance value calculation and the like.
The technical parameters are that three-wire, four-wire or two-wire Pt100/Cu50 thermal resistance signals are directly input; precision, linearity error level: grade 0.2 (relative temperature); a linearization processing and long line compensation circuit is arranged in the circuit; power supply, signal.
Input/output 3000VDC tri-isolation; an auxiliary power supply: 5V, 12V, 15V or 24V direct current single power supply supplies power; international standard signal output: 4-20mA/0-5V/0-10V, etc.; the cost is low, the volume is ultra-small, the use is convenient, and the reliability is high; the standard SIP12/DIP24 conforms to UL94V-0 flame retardant encapsulation; industrial scale temperature range: -40- +85 ℃.
At present, a platinum resistor PT100 of a two-wire system, a three-wire system, and a four-wire system is used for measuring temperature by a thermal resistance method, wherein the two-wire system and the three-wire system are greatly influenced by a lead wire, and in addition, an error of a temperature measuring circuit is greatly influenced by a constant current source circuit. In an industrial control system, temperature data often need to be transmitted over a long distance, and external factors have a large influence on the data.
Disclosure of Invention
The invention aims to solve the technical problems in the related art to a certain extent at least aiming at the defects in the prior art, and provides a PT100 temperature collector with Modbus485 communication function so as to achieve the purposes of measuring temperature and transmitting data more stably, reliably, safely, efficiently and accurately.
In order to solve the technical problems, the technical scheme of the invention is as follows: a PT100 temperature collector with Modbus485 communication comprises a three-wire platinum thermal resistor, a direct-current voltage conversion module, an improved bridge module circuit, a temperature signal amplification module circuit, an analog-to-digital conversion circuit, an MCU module circuit and a 485 communication module circuit;
the platinum thermal resistor is connected with the improved bridge module circuit, the improved bridge module circuit is connected with the temperature signal amplification module circuit, the temperature signal amplification module circuit is connected with the analog-to-digital conversion circuit, the analog-to-digital conversion circuit is connected with the MCU module, the MCU module is connected with the 485 communication module circuit, and the direct-current voltage conversion module provides proper working voltage for circuit components.
As specific embodiments of the present invention, the following may be preferred: the first pin of the platinum thermal resistor in the three-wire system is connected with an analog ground end through a resistor, and the improved bridge module circuit comprises a resistor R5, a resistor R2, a resistor R6, a resistor R3, a capacitor C2 and a capacitor C1;
a second pin of the platinum thermal resistor is connected with one ends of a capacitor C2 and a resistor R5, the other end of the capacitor C2 is connected with an analog ground end, the other end of the resistor R5 is connected with one end of a resistor R10 and one end of a resistor R2, the other end of the resistor R4 is connected with a first voltage source, and the other end of the resistor R2 is used for outputting a first signal;
the second pin of the platinum thermal resistor is connected with one ends of a resistor R6, a capacitor C1 and a resistor R3, the other end of the resistor R6 is connected with a first voltage source, the other end of the capacitor C1 is connected with an analog ground end, and the other end of the resistor R3 serves as a second signal output end.
As specific embodiments of the present invention, the following may be preferred: the temperature signal amplification module circuit comprises a chip U4, a first signal output end and a second signal output end are respectively connected with the input end of the chip U4, and a matched peripheral circuit of the chip U4 is provided with an amplified signal output end.
As specific embodiments of the present invention, the following may be preferred: the analog-to-digital conversion circuit comprises a chip U5 with the model of MCP3202, wherein the chip U5 is connected with the amplified signal output end and collects temperature analog signals, the digital signal output end of the chip U5 outputs temperature digital signals, and the temperature digital signals are provided for the MCU module circuit.
As specific embodiments of the present invention, the following may be preferred: the MCU module circuit is a chip minimum system circuit taking a chip U7 with the model number of STM32F103 as a core.
As specific embodiments of the present invention, the following may be preferred: the 485 communication module circuit comprises a chip U3, a transient voltage suppressor D2, a transient voltage suppressor D3, a resistor R10, a resistor R11, a resistor R12 and a resistor R13;
the model of the chip U3 is SP3485E, the chip U3 is in circuit communication connection with the MCU module, a seventh pin of the chip U3 is connected with a cathode of the transient voltage suppressor D2, one end of a resistor R10 and one end of a resistor R12, the cathode of the transient voltage suppressor D2 is grounded, the other end of the resistor R10 is grounded, and the other end of the resistor R12 is one end of a communication interface;
the sixth pin of the chip U3 is connected to the cathode of the transient voltage suppressor D3, one end of the resistor R11, and one end of the resistor R13, the anode of the transient voltage suppressor D3 is grounded, the other end of the resistor R11 is connected to the second voltage source, and the other end of the resistor R13 is the other end of the communication interface.
As specific embodiments of the present invention, the following may be preferred: the second voltage source is the power supply voltage of the chip U3, the resistances of the resistor R10 and the resistor R11 are equal, and the resistances of the resistor R12 and the resistor R13 are equal.
As specific embodiments of the present invention, the following may be preferred: the capacitance value of the capacitor C2 is equal to that of the capacitor C1, the resistance values of the resistor R6 are equal to that of the resistor R4, and the resistance values of the resistor R2 are equal to that of the resistor R3.
As specific embodiments of the present invention, the following may be preferred: the direct current voltage conversion module also converts the 3.3V voltage into 2.5V reference voltage through a reference voltage source circuit to output.
As specific embodiments of the present invention, the following may be preferred: and the analog ground terminal on the analog-to-digital conversion circuit is connected with the ground terminal through an inductor, or a spiral lead, or a zero-ohm resistor.
The technical effects of the invention are mainly reflected in the following aspects: the technical prejudice that the temperature measurement by the thermal resistance method is poor in three-wire system temperature monitoring precision and unreliable in measurement is overcome, the improved bridge module circuit is adopted, the temperature signal amplification module circuit is matched, the signal transmission reliability can be improved while the temperature data acquisition precision is effectively improved, signals after amplification are subjected to signal conversion by the aid of the analog-to-digital conversion circuit, the conversion precision is guaranteed by supplying power to the bridge circuit module by the aid of a high-precision reference source, the temperature acquisition is improved, and the more advanced, more convenient and more reliable environment temperature and humidity monitoring scheme is provided.
Drawings
FIG. 1 is a block circuit diagram of an embodiment of a module;
FIG. 2 is a schematic diagram of a modified bridge module circuit, a temperature signal amplifying module circuit and a reference voltage source circuit in an embodiment;
FIG. 3 is a schematic diagram of an embodiment of an analog-to-digital conversion circuit;
FIG. 4 is a schematic diagram of an MCU module circuit in an embodiment;
FIG. 5 is a schematic diagram of a 485 communication module circuit in an embodiment;
fig. 6 is a schematic diagram of a dc voltage conversion module in an embodiment.
Reference numerals: 100. a platinum thermal resistance; 200. a DC voltage conversion module; 210. a 5V output circuit; 220. a 3.3V output circuit; 300. improving the bridge module circuit; 400. a temperature signal amplifying module circuit; 500. an analog-to-digital conversion circuit; 600. an MCU module circuit; 700. a 485 communication module circuit; 800. a reference voltage source circuit.
Detailed Description
The embodiments of the present invention will be described in detail below, examples of which are illustrated in the accompanying drawings, and the embodiments described below by referring to the drawings are exemplary and intended to explain the present invention so that the technical aspects of the present invention can be more easily understood and appreciated, and are not to be construed as limiting the present invention.
485 communications in the industry often employ the Modbus protocol. As briefly described herein.
Multi-machine communication: firstly, 485 communication can be networked to realize multi-machine communication, a plurality of transceivers are allowed to be hung on a bus, and from the view of the existing RS485 chip, drivers of different devices such as 32, 64, 128, 256 and the like can be hung.
Modbus protocol characteristics: the Modbus protocol is a general protocol applied to electronic controllers. With this protocol, controllers can communicate with each other, controllers via a network (e.g., ethernet) and other devices, and has become an industry standard. With the device, control devices produced by different manufacturers can be connected into an industrial network for centralized monitoring. This protocol defines a data structure that the controller can recognize as being used regardless of the network over which they communicate. It describes the process of the controller requesting access to other devices, how to respond to requests from other devices, and how to detect error records, which defines a common format for the format and content of the communication data.
In the case of multi-machine communications, the Modbus protocol provides that each controller must know their device address, recognize the data sent according to the address, determine whether to take action, what action to take, and if to respond, send the generated feedback information using the Modbus protocol.