【正文】 n be fairly leisurely. When the data from channel 1 has been sent, the process is repeated for Channels 24. Noise pickup was noted on unused data pins of the microprocessor bus (a 16bitwide bus with only 14 data lines). If these unused pins are configured as inputs, the noise faithfully masquerades as intermittent data. Fortunately, however, a simple software AND function filters out the induced noise and they say digital filtering is tough! As an alternative, you can configure the unused ports as outputs. The above code works perfectly, but establishing correct circuit performance can prove difficult. The interrupt pulse from the 181。 just the voltage levels, slew rate, and connector details. The MAX3100 and MAX202E, however, handle all the standards for making data pliant with RS232, and in a protocol expected by the PC. The Windows Interface The Windows program was written in Visual Basic Version 6. It takes readings from the RS232 port using the MSComm function, configured to accept text, and converts this data to ASCII. It also translates each 16bit data block back to the voltage and current measurements obtained from analogsensing circuitry that precedes the ADC input. From these results, the input power, output power, and efficiency are calculated and displayed on the PC screen, rounded to three decimal places. In addition, the system can freeze the results if they need to be logged. The measured efficiency figures were far from consistent. This was accounted for by noticing ripple on the current and voltage waveforms. The resistors were bypassed with 10nF capacitors to reduce the currentripple readings, but the resistivedivider works measuring voltage were left unbypassed. Thus, the measured ripple (20mV on the input and 100mV on the output) accounted for the 177。10LSB error in 14 bit systems. This error can be trimmed by connecting a trim pot between the output trim pin and ground. It is advisable to switch the reference voltage across both the input and output resistive dividers, and read the input signal to the ADC. From this reading, you can determine errors in the resistive divider chain and implement a software offset. To accurately calibrate the currentsense amplifiers, you must take ADC readings while applying a current source to the input and output, thus obtaining the error in the current amplifier and output resistor. This current source should be set at the minimum expected current reading, because the MAX471 dominant error at low currents is due to input offset voltage contributed by the internal op amps. Conclusions The system under discussion was built up in a series of circuit blocks, and each block was tested individually. This design procedure eliminated a lot of the tension associated with initial powerup of the system. The results taken correspond to those illustrated in the MAX1705 data sheet. Further details of the ponents used in this design can be found on the Maxim web site (). Also available on the website in a zip file () is a full listing of the assembly language code for the Atmel microprocessor (), and the Visual Basic 6 program modules required to run the PC Windows display. Notes 1. Windows is a registered trademark of Microsoft Corp. 2. A full listing of the assemblylanguage code and the Visual Basic program modules is available to download. 3. SPI and Microwire are registered trademarks of Motorola Inc. A similar version of this article appeared in the August 2020 issue of Power Electronics magazine. 更多信息 APP 1138: Jun 28, 2020 MAX125 2x4 通道、同時采樣、 14位數(shù)據(jù)采集系統(tǒng) 完整的數(shù)據(jù)資料 (PDF, 136kB) 免費(fèi)樣品 MAX202E 177。 為 了解 低源阻抗 究竟要有多低，需 考慮一個簡單的數(shù)學(xué)計(jì)算的RC時間常數(shù) . 輸入 電容 大小依據(jù)： vcap = vin (1et/CR), , 其中 C是 取樣電容器 ， R為抗源 ,Vin 是 RC電路 中的應(yīng)用 電壓 . 不同電壓之間vin和 vcap之間在電壓上的不同 是 : vin vcap = vin et/CR 因此 ,已給取樣值 和 hold 電容器 (一般為 10 30pf ) ,電容器 的 充電時間 與誤差電壓是可 接受 的 ( 1 / 2 lsb ) 可以計(jì)算最大允許信號源電阻 ,將 在 一定時間內(nèi)給 電容器 充電 . 輸入緩沖還可以作為一種過濾器清除不必要的信號 . 因?yàn)?ADC 是一種取樣系統(tǒng) ,其輸出光譜具有對稱性偏 約一半的采樣頻率 . 因此 ,信號大于一半的采樣頻率 和 不到一半的采樣頻率 無法區(qū)分信號 . 以 10khz 采樣頻率 為 例 ， ADC 是無法區(qū)分一個 4khz 和 6khz 的輸 入 , 因?yàn)?均 是對稱的大約一半的采樣頻率( 5khz ) . 盡管本條適用范圍 有太多規(guī)定 , 這一效應(yīng) (混 )和定理 ,說明它 (奈奎斯特定理 )描述了許多論文和書籍 . 反走樣過濾器 刪除這些無 用的頻率 . 如果 認(rèn)為該頻譜的任何信號并不是純正弦波 .效果走樣可以相當(dāng)微妙 , 一個非正弦波的定義諧波 ,這些高次諧波將向下造成誤差在較低的頻率 . 另外 ,除非輸入信號頻率范圍是 完全 已知 ， 結(jié)合緩沖 的反鋸齒過濾總是好的設(shè)計(jì)實(shí)踐 . 由于出現(xiàn)問題的系統(tǒng) 只 能 spot readings， 最小過濾是需要的 。 C, 12位系統(tǒng) 是 10ppm / 176。這 樣 一旦確立 , 微處理器 部分 重新接收來自 ADC的數(shù)據(jù)。 測效率數(shù)字遠(yuǎn)遠(yuǎn) 不 一致 （ 性 ）。 PC計(jì)數(shù)器在 第一 時間 復(fù)位 。 10lsb 誤差在 14位 的系統(tǒng) . 這個錯誤可以 修整，通過 連接輸出修 引 腳與地面 . 最好是改用參考電壓的輸入和輸出 電 阻 , 讀出到 ADC的輸入信號 . 從這個 資料 ,能確定錯誤在 反分裂鏈和實(shí)施軟件抵消 . 要準(zhǔn)確地標(biāo)定電流檢測放大器 ， 必須采取 ADC讀數(shù) ， 同時用電流源的輸入與輸出 , 從而 在電流放大器和輸出電阻 取得誤差 . 電流源應(yīng)設(shè)在最低預(yù)期目前閱讀 因?yàn)?max471 在低電流 的在低電流 顯性誤差 ， 是 內(nèi)部 op amps 由于輸入偏移電壓 引起 . 結(jié)論 該系統(tǒng)目前正在討論的是建立 一系列的電路塊 ,每塊單獨(dú)測試 . 這個設(shè)計(jì)程序消除了 與 初始化電力系統(tǒng)相連的 大量的 電壓 . 結(jié)果對應(yīng)這些體現(xiàn)在 max1705數(shù)據(jù)表 . 更詳細(xì)的組件設(shè)計(jì) ,可以 在美信 網(wǎng)站 ( )查找 . 該網(wǎng)站還提供了壓縮文件 ( )是一種正式上市的匯編語言代碼 該微處理器 11 ( ) ,并利用 Visual Basic 6 程序模塊需要運(yùn)行 PC機(jī)視窗展示 . 注 : 1 . Windows 是注冊商標(biāo) ,微軟 2 .匯編 語言代碼和 Visual Basic 程序模塊可供下載 . 3 . SPI 及 Microwire 注冊商標(biāo)摩托羅拉 公司類似的版本 ,這篇文章出現(xiàn)在 2020年 8月發(fā)行 的 電力電子雜志 .