The high-speed refrigerated centrifuge mainly extracts the required components from the liquid mixture. According to the density of each substance, after high-speed rotation, the liquid with high density sinks to the bottom, and the liquid with low density floats on it, so that the liquid is layered. To extract the pure things we need. It is used in many fields such as medicine and chemical industry.
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There are two system inputs: speed input and temperature input. The rotation speed is measured by the optical code, and six pulses are output per revolution. The control is based on the above algorithm. The temperature is measured by ADS90, when the temperature is higher than the set value 2. When C, the compressor starts; when the temperature is lower than the set value 2 ~ C, the compressor stops. In addition, the system has time control. When the motor speed exceeds 500 rpm, it starts timing. Stop when the timer reaches the set time. The output of the system includes the start / stop of the inverter output by the relay, the start / stop of the compressor, the door lock control, and the voltage control speed of 0-5V or 0-10V output by the D / A. Fault detection includes inverter fault, door opening fault, unbalance fault, over temperature fault, and over speed fault. The system has a watchdog.
1 High-speed refrigerated centrifuge software flow
In the prototype debugging, the control subroutines of seven rotor models have been determined, which is suitable for rotors with several thousand to thirty thousand revolutions. In the application, the user only needs to input the rotor model used by the user through the keyboard.
2 System operation results
Control failures and system mechanical failures should be able to detect and alarm in time, close all control objects, and minimize system losses. At the same time, when detecting some failures that do not affect the production, such as damaged buttons or abnormal display, etc., the operator should be alerted and the production should not be stopped.
The way that the hydraulic machine achieves pressure balance adopts the coexistence of pressurization and pressure relief. When the pressure difference (requires pressure-actual pressure) is large, strong pressurization and pressure relief are used for zero output; when the pressure difference is small, weak pressure and pressure relief are zero output; negative pressure (requires pressure-actual pressure is When it is negative, the output mode such as zero pressure and pressure relief should be used. This process is relatively simple in theory, but due to the system response lag phenomenon in the actual control process, its algorithm should be adjusted in the actual commissioning on site to obtain the most satisfactory control results.
3 Problems and solutions in debugging
(1) Because there is a power frequency quenching furnace and an electric welding car next to the production workshop, industrial interference is serious, which has a major impact on the normal operation of the system, and often causes the program to "run away". To this end, we have taken some anti-interference measures. These include:
a. Software anti-interference measures;
b. In addition to adopting white reset measures on the hardware, shielding and isolation measures have been strengthened;
c. Use independent power supply (separated from the interference source) or install UPS power supply;
d. IRC absorption circuit is added to the relay coil. With these measures, the system works normally, and no crashes have occurred.
(2) The sampling signal is unstable, which affects the reliability of the control. Due to the serious interference, it affects the stability of the output signal, resulting in false phenomena in the sampled signal, causing malfunction. We analyzed according to the phenomena that appeared in the scene, and finally added a hardware filter circuit to the front stage to solve this problem.
4 Conclusion
This system is a monitoring system with AT89C51CPU as the main controller, which realizes the automatic control of zinc oxide sheet production. The system is used for production after commissioning, which improves the product qualification rate to more than 98% and greatly improves the economic efficiency. After two years of use, the system is stable and reliable, and never fails. Transfer from: Structure analysis of high-speed refrigerated centrifuge for laboratory