With the advancement and development of science, in vitro culture has become a common method in scientific research work, and the electrothermal incubator is a very important device. Artificial in vitro culture needs to artificially create microorganisms, cells, and bacteria that grow and reproduce in close proximity to the actual living environment of living organisms by controlling certain temperatures, humidity, gas concentrations, and other indicators. The temperature and humidity of the incubator is the most basic indicator. The temperature and humidity control system is the core of the incubator. The level of the control level is the main indicator related to the performance of the incubator. Because the control system of the constant temperature and humidity test chamber is a system with multi-variable, nonlinear, large time delay and strong coupling, the conventional control method has great difficulty in real-time effective control of this kind of complex system. This design adopts the strategy of parallel operation of the Fuzzy-PID controller for temperature control and traditional PID control algorithm for humidity control to improve the performance and quality of the incubator control system. 1 FUZZY-PID control PID control is suitable for deterministic control systems that can establish accurate mathematical models. It has the characteristics of simple structure, good stability and high reliability. The key to PID control is the tuning of PID parameters. In practical applications, due to the complex mechanism of the controlled object or process, it has nonlinearity, time-varying uncertainty, and pure hysteresis. Under the influence of noise and load disturbance, the process parameters change with time and work environment. The PID control effect is not ideal at this time. The two-dimensional fuzzy control, which takes the error and error rate of change as input variables, has proportional and differential control functions, but lacks the integral control function, and the control system reaches a steady state with large errors. The PID control is introduced into the fuzzy controller, and the fuzzy control is combined with the PID control to form a FUZZY-PID compound controller, so that the advantages can be avoided, the fuzzy control is flexible, the adaptability is strong, and the PID control accuracy is high. The system has a faster dynamic response and higher steady-state accuracy. The electric constant temperature incubator is a dual-input dual-output system, and the incubator requires high-precision control of the temperature signal. The traditional PID controller has the ideal linear characteristic near the working point. The fuzzy control method does not need to establish the controlled object mathematical model. It can improve the dynamic performance of the control in the area deviating from the working point. At the same time, it has strong ability to suppress noise and robustness. Better features. The strategy of using Fuzzy--PID control to work in parallel with temperature is adopted. The traditional PID control algorithm is adopted for humidity control, and the temperature and humidity are independently controlled. 2 overall system design The electrothermal incubator provides an in vitro culture environment that is mainly measured by two indicators of temperature and humidity and belongs to a multi-input control system. The overall design can be divided into two major core control systems: thermostatic control and constant humidity control, and buttons, displays, sound and light alarms, and data storage download support systems. The thermostatic system completes the closed-loop control of temperature. The working process can be summarized as follows: the MCU system processes the collected temperature data according to the control algorithm, and the output control quantity is transmitted to the drive circuit, thereby controlling the on-off of the heating heater. Compressor and fan start and stop, so that the temperature reaches the target value, to achieve the control of the box temperature, so the system includes sensor detection, signal processing, MCU control, human-computer interaction systems and power modules. The constant humidity system performs a constant humidity function and is similar to that of a constant temperature system. The MCU system processes the humidity information according to a certain control algorithm, and the control output is transmitted to the driving circuit. The atomizer is controlled on the basis of natural air exchange so that the humidity reaches a set value and the humidity of the cabinet is controlled. 3 system hardware design MCU control unit Refer to SCM cost-effective, use 8-bit microcontroller. Temperature detection unit: Since the integrated temperature sensor has strong anti-interference ability, good linear relationship between temperature and output current, fast response speed, and easy signal conditioning circuit implementation, the design uses an integrated temperature sensor. Humidity detection unit: Humidity detection using digital sensors. Drive control unit: The drive control unit uses SCR to realize the start-stop control of the controlled object. SCR is a non-contact switch, can quickly turn on and off the circuit, power, small size, high efficiency, good stability and reliable operation. Control Execution Unit: The control execution unit includes an electric heat pipe, a compressor, an atomizer, and the like. Human-computer interaction unit: The human-computer interaction unit includes a keyboard, a liquid crystal display, a light emitting diode, a buzzer, and the like. Power circuit: The system uses 220V AC power supply, through the DC power supply circuit for each functional unit to provide DC voltage regulator, including the transformer, rectifier circuit, filter circuit, voltage regulator circuit in four parts. In order to prevent sudden power failure of the AC power supply system and improve the reliability of the electrothermal incubator, a backup power supply consisting of 8 cells of 2400mAh NiMH batteries is connected. 4 system software design temperature and humidity control system software design ideas After the microcontroller is powered on, the system performs self-test and initialization. The system initialization includes modules such as: input/output ports, variables in RAM, stacks, timers, interrupts, displays, ADCs, and so on. After the initialization is completed, it enters the main program. The main program is the loop body that executes the scheduling function. Each function module is stored in the form of a subroutine and is called by the main program and debugged independently. The main program is the core of software design. The working status of all subprograms is managed by the main program. The main program judges the entry condition of each state. When the condition is satisfied, it will switch to the subroutine. After the subroutine has processed the corresponding transaction, it will return to the main program. After the main program resets the program on power-up, it first performs the necessary initialization work for each working module, mainly including the interrupt setting, the input and output mode setting of the peripheral interface, and so on. The software design includes the monitoring program and the design of each application program. It is divided into two phases: overall design and module design. The software design tasks of the electrothermal incubator control system mainly include the following aspects: Information collection: It mainly includes temperature and humidity measurements. The ADC inside the microcontroller converts the collected analog data to digital quantities. Timing, counter as the sampling clock. Sliding filtering is used to eliminate abnormal values, eliminate pulse signal interference, and improve measurement accuracy. Control system design: The output of the SCM controls the fans, compressors, heating pipes, and atomizers in the cabinet to control the temperature and humidity of the cabinet. In a control cycle, timing and counter timing are used, and the pulse width modulation signal PWM is used as an output control signal to improve the accuracy of the execution time of the components. Control algorithm design: For the sampled temperature and humidity data, the microcontroller calculates the output control amount through the control algorithm. The control algorithms include PID control, fuzzy control, two-dimensional interpolation, and floating point processing. Display design: mainly LCD display. The main interface is displayed during system initialization. The temperature, humidity, running time, and status are displayed in real time during the operation. When there is a key operation, the display interface is switched to the setting interface. During the data download process, the status, download status, and results of the storage device are displayed. . Key design: keyboard sampling interrupt mode monitoring, to achieve the switch machine, temperature and humidity target value and run time settings, eliminate alarms and other functions. Data storage download design: At the beginning of each control cycle, the current temperature and humidity data are written into the EPROM. When the USB device is inserted, the remaining space of the device is read first, and then the EPROM data is written into the USB device. Alarm system design: When the temperature or humidity exceeds the set data or the operation is completed, the single-chip microcomputer outputs control signals, and drives the buzzer and light-emitting diodes to perform sound and light alarm. 5 Conclusion The temperature and humidity control system using a single-chip microcomputer as the control chip adopts the strategy of parallel operation of the Fuzzy-PID controller on the temperature control, and adopts the PID control algorithm on the humidity control, making the electrothermal constant temperature incubator work stable, reliable, and strong practicality. Widely used in medical science research. Can achieve temperature control range +5 ~ 50 °C, room temperature 28 °C to set 36.5 °C settling time ≤ 2min, constant temperature fluctuations ≤ ± 0.3 °C, relative humidity reached 80% of the expected indicators.
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