怎样实现PLC与电度表通讯实时采集地面电源用电量,并通过VB界面显示、存储数据，最好有详细程序，万谢！

采用电子电度表，并且该电度表具有数据通信功能（例如Modbus协议）。在建立通信的过程中，将当前值（用电量）减去上次抄表时的电量，就是当前实际用电量。之后再设计VB程序。并完成数据与上位机的通信。

TI公司的ADS8688是基于16位逐次逼近(SAR)模数转换器(ADC)的八路数据采集系统,工作在500kSPs的吞吐量.双极工作电源±10.24 V,±5.12 V和±2.56 V,单极工作电源0 V 到 10.24 V和0 V到5.12 V,输出保护电压高达成±20 V,低功耗65mW,具有极好的性能: SNR: 92 dBTHD:–102 dB.主要用于工业控制,PLC和数据采集系统.本文介绍了ADS8688主要特性,框图,以及在电源自动化和PLC的数据采集系统框图, ADS8688EVM-PDK 评估模块主要特性和GUI主要特性,电路图,材料清单和六层PCB设计图.

The ADS8684 and ADS8688 are 4- and 8-channel, integrated data acquisition systems based on a 16-bit successive approximation (SAR) analog-to-digital converter (ADC), operating at a throughput of 500 kSPS. The devices feature integrated analog front-end circuitry for each input channel with overvoltage protection up to ±20 V, a 4- or 8-channel multiplexer with automatic and manual scanning modes, and an on-chip, 4.096-V reference with low temperature drift. Operating on a single 5-V analog supply, each input channel on the devices can support true bipolar input ranges of ±10.24 V, ±5.12 V, and ±2.56 V, as well as unipolar input ranges of 0 V to 10.24 V and 0 V to 5.12 V. The gain of the analog front-end for all input ranges is accurately trimmed to ensure a high dc precision. The input range selection is software-programmable and independent for each channel. The devices offer a 1-MΩ constant resistive input impedance irrespective of the selected input range.

The ADS8684 and ADS8688 offer a simple SPI-compatible serial interface to the digital host and also support daisy-chaining of multiple devices. The digital supply operates from 1.65 V to 5.25 V, enabling direct interface to a wide range of host controllers.

ADS8688主要特性:

16-Bit ADC with Integrated Analog Front-End

4-, 8-Channel MUX with Auto and Manual Scan

Channel-Independent Programmable Input Ranges:

Bipolar: ±10.24 V, ±5.12 V, and ±2.56 V

Unipolar: 0 V to 10.24 V and 0 V to 5.12 V

5-V Analog Supply: 1.65-V to 5-V I/O Supply

Constant Resistive Input Impedance: 1 MΩ

Input Overvoltage Protection: Up to ±20 V

On-Chip, 4.096-V Reference with Low Drift

Excellent Performance:

500-kSPS Aggregate Throughput

DNL: ±0.5 LSBINL: ±0.75 LSB

Low Drift for Gain Error and Offset

SNR: 92 dBTHD: –102 dB

Low Power: 65 mW

AUX Input → Direct Connection to ADC Inputs

SPI™-Compatible Interface with Daisy-Chain

–40℃ to 125℃ Industrial Temperature Range

TSSOP-38 Package (9.7 mm × 4.4 mm)

图1. ADS8688功能框图

图2. 用于电源自动化的ADS8688八路复用数据采集系统框图

图3. 用于PLC的ADS8688 16位八路综合模拟输出模块框图

ADS8688EVM-PDK 评估模块

The ADS8688EVM-PDK is a platform for evaluating the ADS8688 device. The ADS8688EVM-PDK consists of an ADS8688EVM board and an SDCC controller card. The SDCC is an FPGA-based controller card that functions as an serial peripheral interface (SPI™) host and transfers data to the ADS8688EVM graphical user interface (GUI) via a USB interface. The ADS8688EVM GUI collects, analyzes, and records data from the ADS8688EVM board. The ADS8688EVM GUI is capable of collecting data from the ADS8688EVM in auto and manual modes, configuring the ADC program registers, and performing FFT analysis of data captured from the ADC.

ADS8688EVM-PDK 评估模块主要特性:

• Includes support circuitry as a design example to match ADC performance.

• 3.3-V slave SPI.

• Serial interface header for easy connection to the SDCC controller card.

• Designed for a 5-V analog supply.

• Integrated 4.096-V voltage reference.

• Bipolar (±10.24 V, ±5,12 V, ±2.56 V )or unipolar(0 V to 10.24 V, 0 V to 5.12 V) input ranges for each channel.

• Onboard, second-order, Butterworth, low-pass filters for four channels.

• Onboard regulator for generating a ±15-V bipolar supply for second-order, Butterworth, low-pass filters.

• Capable of accepting a ±100-mV signal on the negative analog inputs (AIN_xGND).

ADS8688EVM-PDK 评估模块GUI特性:

• Captures data from the ADS8688EVM in auto and manual modes.

• Configures the ADS8688 device program registers.

• Enables and disables channels in auto mode.

• FFT analysis and calculates the SNR, THD, and SINAD ac performance parameters.

• Single and multiple graph views for captured data.

• Includes a dc histogram for dc inputs.

• Logs ADC data.

图4.ADS8688EVM-PDK 评估模块外形图: microSD存储卡和SDCC控制板

The ADS8688EVM-PDK includes microSD memory cards that contain the EVM software and SDCC controller board firmware required for the EVM operation

开关电源中电压采样是通过对输出电压进行电阻分压后送到431的基准端进行比较，控制光耦再去控制初级的PWM。电流采样是对取样电阻上的电压检测的方式来进行的。与电压控制环路一样。

开关电源是利用现代电力电子技术，控制开关管开通和关断的时间比率，维持稳定输出电压的一种电源，开关电源一般由脉冲宽度调制（PWM）控制IC和MOSFET构成。随着电力电子技术的发展和创新，使得开关电源技术也在不断地创新。目前，开关电源以小型、轻量和高效率的特点被广泛应用几乎所有的电子设备，是当今电子信息产业飞速发展不可缺少的一种电源方式。

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