【正文】 各檔的所允許的測量誤差得出最大誤差測量電阻值，將 R的誤差與測量最大誤差進行比較得出萬用表的自身誤差值，進而是實現(xiàn)校驗。此方案正在繼續(xù)實驗中。 方案三：采用恒流源電路，針對指針式萬用表進行設(shè)計。 方案二：應(yīng)用電子負載的原理在輸出端口處等效電阻特性，實現(xiàn)電阻的輸出。標準電阻采用高精度系列電阻組成，采集電路的到的數(shù)值給 cpu處理，并顯示在液晶屏上。 基于 STM32的數(shù)字化萬用表校驗儀開發(fā) 第 6 頁 4 項目功能實現(xiàn) 電阻檔電路設(shè)計 由于電阻檔的任務(wù)就是向輸出端口提供一個具有一定精確度的電阻，并提供參考電阻值。電阻檔必要時需要用到單片機。 ： 任務(wù) A：電阻網(wǎng)絡(luò)單元電路 任務(wù) B：電流源單元電路 任務(wù) C：逆變器單元電路 任務(wù) D：采集單元電路 任務(wù) E：電源單元電路 ： 任務(wù) F：交互界面模塊 任務(wù) G： A/D采集模塊 任務(wù) H：電阻檔控制輸出 任務(wù) I：電流源控制輸出 任務(wù) J：電壓檔控制輸出 ： 基于 STM32的數(shù)字化萬用表校驗儀開發(fā) 第 5 頁 F、 G、 E、 (A/B/C)、 D/H/I、 J 注： F、 G、 E：交互、 A/D 模塊、供電電源為整機各結(jié)構(gòu)中均有用到的。 （ 2）電流源網(wǎng)絡(luò)：設(shè)計制作一個輸出電流數(shù)控可調(diào)的電路，并有微調(diào)功能；包含程序模塊，并為 嵌 入整機程序留好端口。 6．采用自校準技術(shù)，減少了器件老化對測量結(jié)果的影響，延長校驗儀的壽命。 2．采用數(shù)字化閉環(huán)技術(shù)，解決市面上測量不準，抗干擾能力差的問題，提高校驗儀的準確度和穩(wěn)定性。我們結(jié)合學(xué)校實訓(xùn)教學(xué)特點，針對“學(xué)生校表難，老師打分難”等問題在幾年前曾研發(fā)了第一款萬用表校驗儀，在使用中發(fā)現(xiàn)了電壓輸出不穩(wěn)，校驗儀本身不能自校準，顯示不清晰，器件老化精度降低等問題。 Abstract The multimeter is one of the necessary instrumentation electrician, each electronic engineers should master the principle and method of use. Often need to produce their own multimeter calibration table students training process in million, so as to make himself with a multimeter more accurate. After the teacher training according to the production situation of students to give students making results, we should not only see through the production process of students but also on the students of the multimeter test. The project bines the teaching characteristics of school training, the multimeter check specific problems in teaching, such as output voltage instability, checking instrument is not calibrated, display is not clear, the problem reduced precision devices such as aging, is proposed based on the original million meter calibrator on upgrading, in order to better service for the teaching. The project was designed more tightly on the overall plan, in order to realize the functions of presupposition, the resistance profile unit, current gear unit, voltage unit, control circuit unit and a power supply circuit unit of parison and demo nstration of various options, the final selection is an economical, simple, practical design, realizes the required function. The project has carried on the summary to some problems in the research process, further development of the subsequent function provides a reference. 目 錄 1 引言 ..............................................................................................................................................................1 2 項目研究的主要內(nèi)容 ................................................................................................................................2 3 項目研究的總體方案設(shè)計 ........................................................................................................................3 整機結(jié)構(gòu)分析 .....................................................................................................................................4 任務(wù)分解方案 .....................................................................................................................................4 4 項目功能實現(xiàn) .............................................................................................................................................6 電阻檔電路設(shè)計 .................................................................................................................................6 電流檔電路設(shè)計 .................................................................................................................................8 方案分析 ....................................................................................................................................8 電流檔恒流源設(shè)計 ....................................................................................................................9 方案原理說明及有關(guān)計算 .................................................................................................... 10 電壓檔電路設(shè)計 .............................................................................................................................. 10 方案分析 ..................................................................................................................................11 關(guān)于 VCA810的壓控放大器的說明 ..................................................................................... 13 電壓檔測量電路 ..................................................................................................................... 14 ............................................................................................................. 16 控制電路設(shè)計 .................................................................................................................................. 17 光電耦合電路 ......................................................................................................................... 17 TIP521的參數(shù) ........................................................................................................................ 18 電路設(shè)計思路 ......................................................................................................................... 19 電源電路設(shè)計 .................................................................................................................................. 20 電源電路的組成 ..................................................................................................................... 20 電源電路改進思路 ..............................................................................................