Research And Development Of Controller For Multi-input-multi-output Liquid Level Control System

In the fields of energy,chemical industry,metallurgy,biological and other industries,the high-precision real-time control of liquid level is widely used in boilers,liquid storage tanks,melting pools,return pools and other equipment.And the liquid level control system of multi-input-multi-output not only has the characteristics of nonlinearity,strong coupling and flexibility,but also can simulate the liquid level control in industrial production through the pumps and valves.The higher the sampling accuracy of the liquid level controller,and the more accurate the control of the actuator,the better the control accuracy of the liquid level.The original multi-input-multi-output liquid level controller of the laboratory adopts single-channel selective liquid level signal acquisition mode,which can sample 16 bit ADC in time-sharing,and uses a timing valve control strategy,which can carry out multiple experiments including single liquid level,double liquid level,three liquid level control.However,there are some problems in the controller,such as unreasonable PCB wiring,low accuracy of liquid level collection,slower sampling frequency,and inability to accurately adjust the degree of opening of valve,resulting in the control accuracy cannot meet the requirements.Therefore,in this paper,we optimized the controller from two aspects of hardware and software.The research content mainly includes the following aspects:(1)In terms of hardware,we take ADuCM360 chip as the control core,and modularize integration of the acquisition and control circuits,respectively,and design the step-down filter for the liquid level signal and flow signal acquisition circuits.By building a common emitter amplifier circuit,the pump control signal is stably output,and the valve control circuits are designed with I2 C bus and latch.And the power management module is treated with bead isolation,capacitance filtering,grounding,and PCB is improved from double-sided board to four-layer circuit board,which increased wiring area.The optimized design enables the controller to perform 24-bit ADC sampling,and the adjustment time of the pump control circuit output signal is at about 6 milliseconds,and controller can filter out clutter with a frequency higher than 1.6 k Hz in the flow signal,and the PCB's digital area and analog area are avoided staggered wiring.Power supply noise interference of the controller is effectively suppressed.(2)In the bottom software,we adopt the idea of modularization,and use the control flow of multiple nested selection cycle structure.The controller adopts the method of multi-channel parallel liquid level signal acquisition.The technology of limiting average filter and visual calibration is used to process the sampling value of liquid level,and the segmented valve control strategy is adopted.The design improvements improve the execution efficiency of the program,shorten the sampling period to 0.5 seconds,and the sampling error can be reduced to ±1 millimeter,The valve opening can be controlled more accurately within 20% ? 45%.(3)During the test of the circuit characteristic,the output voltage pulse signal of the flow signal acquisition circuit will occasionally rise suddenly,and it will exceed the upper limit of the input voltage signal allowed by the chip.So we through double operational amplifier and filter circuit to stabilize the peak voltage of the output pulse signal at 2.325 volts,which suppresses the burr noise.In addition,the controller passed the fourth level test of ESD immunity and the third level test of electrical fast transient pulse group.In the single liquid level control test,the system regulation time is shortened by 2.5 seconds,and in the double liquid level control test,the lag time of the system is shortened by 2 seconds,the adjustment time of the liquid level 1 and the liquid level 2 are respectively shortened by 17.5 seconds and 4.5 seconds.The test results show that the controller designed has good anti-interference,high reliability,fast response speed,small fluctuation of liquid level curve,and effective improvement of liquid level control accuracy.