Operating System, Motor Control System Introduction With the development of computer technology, the original analog industrial process controller was gradually replaced by a digital controller. In various digital control systems, using control cards and thinking that the industrial process control system of the operation platform has been provided with a friendly operation interface and perfect multimedia functions, it has been obtained in process control in which the response time of the system such as chemical reaction and heat treatment is long. widely used. In the case of objects with small time constants such as motors, the control cycle of such control systems is relatively long. In actual applications, the control system with or as the core is often used. Usually, in order to visualize the state of the controlled object, The serial port is used to upload data to the industrial computer for display. Such a system not only achieves control of small time constant objects, but also visually reflects the state of the objects. However, because the control core is HI G FJ, it is difficult to implement complex control algorithms such as neural networks and fuzzy control in the control, as well as the switching and comparison between multiple algorithms. This is exactly the result of student experiments and scholars. For the purpose of the motor experimental system required. In the system developed by the author, the controlled object is a set of experimental DC motors. The electromagnetic time constant is approximately MM0, and the motor's control is achieved by changing the phase shift trigger angle of the rectifier thyristor. The control strategy uses speed and current double closed-loop regulation. The successful development of this system provides an experimental platform for experimenting with various complex algorithms for controlling the motor, so that the algorithm can be better applied to the actual production. During the development process, issues such as the influence of external process on the system control cycle, inaccurate speed setting input ripple, and strong motor-to-computer interference have occurred. How to solve these problems is often an industry that uses control cards and believes that the operating platform is The success or failure of the process control system has an important influence. The author puts forward some effective methods for reference by his own development practice. System Overview The control system first samples the speed, speed setting, and current of the DC motor, then uses the speed as the feedback and the speed as the given value. The result is a given value of the current loop operation, and the current loop Feedback is the sampled value of the current. The output of the system is the result of the operation of the current loop, which controls the phase-shift firing angle of the thyristor. The software is used for development, mainly including the parameter setting in the algorithm, the control of the card, the calculation output according to the sampling data and the control algorithm, and the real-time display of parameters such as motor current and speed. The hardware of the system is mainly the thyristor drive circuit of the motor, the sampling of current and speed, the conditioning circuit, the control card, and the optocoupler circuit between the motor and the computer. In order to effectively conduct galvanic isolation, the current is rectified after sampling from the AC-side thyristor rectification system based on the '(), platform's motor experimental control system based on the platform's motor experimental control system "industrial control computer" in the first volume of the year. Speed ​​is obtained with a speed generator. The two signals and the speed setting are connected to the input of the control card by photoelectric isolation. The control card is based on the reference 'The sampling period is the time constant of the controlled object'. In consideration of the time constant of the controlled object, we have chosen Advantech's type sampling control card. The card has analog input analog output. For or equivalent products, the bits are successively compared and the conversion time is 12. With the driver program provided by Advantech, the analog input range can be set. The test card allows maximum continuous overvoltage: for a bit or equivalent product, the analog output range is up to and up to 9)4, the output setup time is)! 2. If the calculation time is not taken into consideration, then the minimum control period that the card can achieve is the influence of the platform and other factors. In practice, when the development is based on the system, the driver must be installed first. This is followed by In programming, you can use the standard function to operate after adding the file export library to the project. Several problems encountered in the development and solutions In the development of the system, the author encountered such as the system control cycle is affected by external threads indefinite, there is a strong common-mode interference in the motor current, speed signal and the speed setting ripple The big problems, after efforts to put forward the corresponding solutions. Determining the system control cycle system is a preemptive, multi-threaded operating system, which provides a good platform for relatively slow applications such as multimedia, databases, and networks. However, because industrial process control generally requires strict time intervals, the multithreading mechanism allocates time among all threads to achieve the effect of multitasking. In this way, if there are other threads running outside the industrial control thread, the thread control is controlled. The cycle will inevitably be affected. This is especially true for control systems where the controlled object has a small time constant. According to the reference, there is a timer interrupt operation mode, which is to use the inherent crystal oscillator on the card to count the output signal, when the preset value is reached, generate an interrupt signal and trigger the sampling, and read the interrupt after the detection The sampled values ​​are calculated and the output is completed, thus completing a control loop. Due to the use of hardware-timed trigger sampling, the accuracy of the system control cycle is greatly improved. To configure the parameters required for the interrupt, etc., to provide functions for the driver. Fig. Hardware timing sampling process Isolation between motor input signal and computer As the motor will generate inrush current and overvoltage during startup and shutdown, if the control card shares the ground with the motor, it will generate input signals such as speed and current. Huge common-mode interference is not conducive to measurement and control; at the same time, exceeding the allowable overvoltage of the control card will also cause serious damage to the control card. Therefore, it should be considered that the control card is isolated from the motor. DC motor current, speed and other signals for the amount of DC, transformer isolation can not be used. At this time, the use of high-precision linear optocouplers is much cheaper than the conversion-based isolation method. For the company's high-precision linear optocoupler, using the package, the frequency response range of the stability of the peak isolation voltage, can better meet the requirements of the system. It can be used to compensate for the transmission gain error due to the discreteness of the device, so that the stability of the ripple speed setting signal equal to removing the speed setting signal by non-linear filtering has a platform-based motor experimental control system for motor cascade speed regulation. Importantly, if it contains ripple, the system will inevitably oscillate. In order to obtain a stable set signal, the potentiometer is used to obtain the set signal by dividing the voltage of the DC power supply. However, due to the interference of the motor circuit, there exist harmonics of the second and higher harmonics. If no direct processing is used, the speed signal is used. There are the same harmonics. If an ordinary linear phase filter is used, there will be a large negative impact on the step response of the system due to the long delay. Figure isolation circuit wiring diagram using a variable structure of nonlinear filtering can better meet the two requirements. In order to perform filtering, a point queue is first generated. When the first sampling is completed, the average value of the first sampled value in the queue and the average value of the first sampled value is compared with the first sampled value. If it is satisfied, the set signal may be considered. In the steady state, the first sampled value is moved into the queue and used as the filtering result; if the above formula is not satisfied, the setting signal is suddenly changed, and the data in the queue is all set as the filtering result output. In general, to ensure that the signal is stable in the filter characteristics; take (), both to improve the smoothness of the signal, but also to avoid a large filter delay; can be set according to need. The above filtering method can not only quickly reflect the change of the signal when the signal is mutated, but also can smooth the signal when the signal is steady. The results of the control and discussions are determined. The current loop and speed loop in the figure are all standards. /0 Controls the result of the algorithm. The current loop in the figure is the standard. /0, speed loop is integral saturation. /0 control result. The current curves in the two figures are at the maximum due to hardware current limiting. Including: speed setting curve; speed curve; current curve; differential and integral time parameters. Both rings are standard. Start curve of /0 Where: Current loop Parameters: Speed ​​loop Parameters: Diagram The speed loop is saturated. Start curve of /0 Among them: Current loop parameters: Speed ​​loop Parameters: Speed ​​loop Integral saturation value: In summary, the platform-based motor process control system can realize complex control algorithms compared to the core control system, and is flexible. The comparison between various control strategies. If you have a better control card, you may be able to complete the higher-speed control tasks required.
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