Temperature telemetry and remote control system based on C8051F04O single chip microcomputer

O Introduction
Temperature remote control and telemetry is a remote measurement and control of temperature. It is particularly suitable for those places where the environment is harsh and the measurement personnel are not easy to approach. In recent years, it has been widely used in industrial and agricultural production. According to the characteristics of the remote control and telemetry system, a design scheme for water temperature remote control and telemetry is proposed.

1 Overall design
The temperature remote control and telemetry system is mainly composed of a microprocessor system, a temperature measurement module, a heating module, a communication module, a liquid level module, and a host computer software. The system structure is shown in Figure 1.

After the temperature measuring module measures the temperature of the liquid, it sends the temperature value to the microprocessor. When the temperature change reaches a certain value, the heating module starts heating. First, it can heat to the set temperature within the set time and stabilize at the temperature for a period of time. The system can also perform segmented zigzag heating according to the designed temperature nodes with high accuracy. The liquid level measuring module measures the liquid level in real time and transmits it to the microprocessor. The system realizes telemetry and remote control through two communication modules. After the host computer sets the temperature parameters, it transmits them to the remote microprocessor through the communication module. The microprocessor controls the heating module to heat according to the temperature set by the host computer. At the same time, the microprocessor transmits the liquid temperature and liquid level height to the host computer software through the communication module. The liquid temperature and height can be displayed and monitored in real time through the host computer software interface. The display module displays the system's temperature, height and other data on the LCD screen in real time.
The program uses the PID algorithm to establish proportional, integral and differential mathematical models to control the TCA785 phase-shift trigger to positively and negatively trigger the thyristor BAT-20 to heat the heated material. The phase-shift triggered bidirectional thyristor has accurate and stepless voltage regulation, which better integrates the contradiction between overshoot and heating time; remote sensing and telemetry use PTR-2000 to communicate with the host computer, and the water temperature can be set and controlled arbitrarily within the range of 0 to 100℃. PTR-2000 has a long communication distance and high accuracy. The PC interface displays the temperature curve in real time, and the upper and lower limits of temperature and liquid level are set. It also has the functions of setting the temperature curve sampling rate and printing the temperature curve. [page]

2 Hardware Design
The system hardware mainly consists of C8051F040 single-chip microcomputer minimum system, PTR2000 wireless communication module, TCA785 phase-shift voltage control module, Ptl00 temperature measurement module, WDK505 liquid level measurement module, etc.
2.1 C8051F040 single-chip microcomputer minimum system
The minimum system is based on the single-chip microcomputer C8051F040, including crystal oscillator circuit, reset circuit, anti-interference circuit, voltage reference circuit and power supply part. C805lF040 single-chip microcomputer is a fully integrated mixed signal system-level core SoC produced by Cygnal Company in the United States. It has 64kB Flash, 4352BRAM, CAN controller 2.0, two serial interfaces, 5 16-bit timers, 12-bit A/D converter, 8-bit A/D converter and 12-bit D/A converter, etc. It also has a JTAG interface inside, which makes debugging very convenient.
2.2 PTR2000 wireless communication module
This device combines reception and transmission into one, and its operating frequency is the internationally used digital transmission frequency band of 433MHz; it adopts FSK modulation/demodulation, can directly enter data input/output, and has strong anti-interference ability. This template block integrates high-frequency reception, PLL synthesis, FSK modulation/demodulation, parameter amplification, power amplification, channel switching and other functions. The communication distance can meet the design requirements. In the design circuit, part of PTR2000 is connected to the computer serial port after level conversion through MAX232, and the other part is connected to the minimum system.
2.3 TCA 785 phase-shift voltage regulation control module
The heating module is realized by a phase-shift trigger integrated trigger. The trigger TCA785 has a high recognition ability of zero crossing, a wider phase shift range, and a better uniformity of the output pulse, which can make the controlled element change steplessly from 0V to 220V. It is often used under conditions with high precision requirements and harsh controlled environment. Phase-shift triggering achieves voltage regulation by changing the voltage-adjusting conduction angle. The voltage and average power across the load change with the change of the phase-shift triggering angle. In each positive or negative cycle of the thyristor, there is a part that keeps on and off, that is, the output is continuously adjustable and can adapt to loads of various properties. This system sets a master control switch for the heating unit. The upper computer can directly control the on and off of the switch and use a light bulb to display the switch status. The control principle diagram is shown in Figure 2.

2.4 Ptl00 temperature measurement module
The Ptl00 temperature sensor is a positive temperature coefficient thermistor sensor with the advantages of anti-vibration, good stability, high accuracy, and high pressure resistance. The linearity of the platinum thermal resistor is good. When it changes between 0 and 100°C, the maximum nonlinear deviation is less than 0.5°C. The relationship between the resistance value of the platinum thermal resistor and the temperature is:

In the formula, A=0.00390802; B=-0.000000580; its resistance expression can be approximately simplified as: Rpt00=100×(1+At), when the temperature changes by 1°C, the resistance value of Ptl00 changes approximately by 0.39 Ω.
2.5 WDK505 liquid level measurement module
The WDK505 pressure transmitter is used to measure the liquid level. The instrument has the advantages of anti-condensation, anti-lightning design, strong anti-interference ability, and good long-term stability. The chip is placed in a fully stainless steel shell and is firmly sealed, with good reliability and high precision.

3 Software Design
The main task of this system is to initialize the C8051F040 chip and set and communicate various parameters, and display them. The focus is on overshoot control, temperature control PID implementation, and the writing of the host computer software.
3.1 Overshoot control
Experiments show that in the water temperature control system, the general control always has a large overshoot, and can only rely on natural cooling, which greatly prolongs the adjustment time. Therefore, in order to shorten the adjustment time in the water temperature control system, it is necessary to achieve basically no overshoot. Through repeated experiments, the PID algorithm and fuzzy control method are added to the program for temperature control. Practice has proved that this control method can speed up the system step response, reduce overshoot, and has a higher temperature control accuracy.
3.2 Host computer software
The host computer software is written in VC++, which can set the upper and lower limit temperatures and liquid levels of 2 channels, as well as the real-time display of temperature and liquid level and the temperature change curve over time. The host computer software can print the temperature curve, which can be printed in full or in part, and can also view historical data at any time. Its interface is shown in Figure 3.

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3.3 PID implementation of temperature control
PID control is a control strategy with mature technology and wide application in control engineering. After long-term engineering practice, a complete set of control methods and typical structures have been formed. The basic principle of PID is: due to the continuous generation of various disturbances from the outside world, in order to achieve the purpose of keeping the value of the field control object constant, the control action must be carried out continuously. If the disturbance occurs and causes the value of the field control object to change, the field detection element will collect this change and send it to the input end of the PID controller through the transmitter, and compare it with its given value to obtain the deviation value. The regulator will send a control signal according to this deviation and the control law of the setting parameters we set in advance to change the opening of the regulator to increase or decrease it, so that the value of the field control object changes and tends to the given value, thereby achieving the control purpose. In fact, the essence of PID is to perform proportional, integral and differential operations on the deviation, and control the execution component according to the operation results. The control scheme is shown in Figure 4.

The control law of the PID controller can be described as:

This design utilizes the positional PID algorithm introduced above, takes the temperature sensor sampling input as the current input, then subtracts it from the set value to get the deviation, then performs PID operation on the deviation value to generate the output result, and finally controls the timer time to control the heater.

4 Conclusion
Temperature remote control and telemetry is a control technology that is widely used in industry. This article is an exploration and practice of temperature remote control and telemetry. The design uses PID control algorithm to greatly reduce overshoot and improve control accuracy. Since the sensor and other devices themselves are not ideal linear, the program performs linear compensation on the measured data. After a large number of experiments, observation data, and system optimization, the final experimental results are of high accuracy. The water temperature control is accurate, the two-way communication is good, and the upper computer interface is complete and beautiful. I hope that the solution proposed in this article can help and inspire everyone in the design and application of temperature remote control and telemetry.