畢業(yè)設(shè)計(jì)單片機(jī)溫度控制英文文獻(xiàn)-展示頁(yè)
2024-12-14 08:17本頁(yè)面
【正文】 ays of setpoint and actual temperatures and that setpoint temperature entry should be digital as well as opposed to say through a potentiometer setting 3 System Design The requirements for digital temperature displays and set point entry alone are enough to dictate that a microcontroller based design is likely the most appropriate Figure 2 shows a block diagram of the students design The microcontroller a MotorolaMC68HC705B16 6805 for short is the heart of the system It accepts inputs from a simple fourkey keypad which allow specification of the setpoint temperature and it displays both setpoint and measured chamber temperatures using twodigit sevensegment LED displays controlled by a display driver All these inputs and outputs are acmodated by parallel ports on the 6805 Chamber temperature is sensed using a precalibrated thermistor and input via one of the 6805s analogtodigital inputs Finally a pulsewidth modulation PWM output on the 6805 is used to drive a relay which switches line power to the resistive heater off and on Figure 3 shows a more detailed schematic of the electronics and their interfacing to the 6805 The keypad a Storm 3K041103 has four keys which are interfaced to pins PA0 PA3 of Port A configured as inputs One key functions as a mode switch Two modes are supported set mode and run mode In set mode two of the other keys are used to specify the setpoint temperature one increments it and one decrements The fourth key is unused at present The LED displays are driven by a Harris Semiconductor ICM7212 display driver interfaced to pins PB0 PB6 of Port B configured as outputs The temperaturesensing thermistor drives through a voltage divider pin AN0 one of eight analog inputs Finally pin PLMA one of two PWM outputs drives the heater relay Software on the 6805 implements the temperature control algorithm maintains the temperature displays and alters the setpoint in response to keypad inputs Because it is not plete at this writing software will not be discussed in detail in this paper The control algorithm in particular has not been determined but it is likely to be a simple proportional controller and certainly not more plex than a PID Some control design issues will be discussed in Section 4 however 4 The Design Process Although essentially the project is just to build a thermostat it presents many nice pedagogical opportunities The knowledge and experience base of a senior engineering undergraduate are just enough to bring him or her to the brink of a solution to various aspects of the problem Yet in each case realworld considerations plicate the situation significantly Fortunately these plications are not insurmountable and the result is a very beneficial design experience The remainder of this section looks at a few aspects of the problem which present the type of learning opportunity just described Section 41 discusses some of the features of a simplified mathematical model of the thermal properties of the system and how it can be easily validated experimentally Section 42 describes how realistic control algorithm designs can be arrived at using introductory concepts in control design Section 43 points out some important deficiencies of such a simplified modelingcontrol design process and how they can be overe through simulation 41 Mathematical Model Lumpedelement thermal systems are described in almost any introductory linear control systems text and just this sort of model is applicable to the slide dryer problem Figure 4 shows a secondorder lumpedelement thermal model of the slide dryer The state variables are the t
公司管理相關(guān)推薦
鄂ICP備17016276號(hào)-1