真有效值AC-DC转换器AD736及其在RMS仪表电路中的应用

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基于单片机的工频电压(电流)表的设计

检测系统实习报告题目：基于单片机的工频电压（电流）表的设计姓名：院（系）：专业：指导教师：职称：评阅人：职称：年月摘要在实际中，有效值是应用最广泛的参数，电压表的读数除特殊情况外，几乎都是按正弦波有效值进行定度的。

有效值获得广泛应用的原因，一方面是由于它直接反映出交流信号能量的大小，这对于研究功率、噪声、失真度、频谱纯度、能量转换等是十分重要的；另一方面，它具有十分简单的叠加性质，计算起来极为方便。

本文详细介绍了一个数字工频电压、电流表设计，以AT89S52单片机为控制核心，由电压、电流传感器模块，真有效值测量模块，信号调理模块，AD采集模块及控制、显示模块等构成。

系统采用电压、电流互感器对输入信号进行降压处理，经AD736转换得到原信号的真有效值，由TLC549转换为数字量后送入单片机内进行简要的数据处理并将结果通过LCD实时显示，达到了较好的性能指标。

关键词：工频数字电压（电流）表真有效值AD736 TLC549 AT89S52AbstractIn practice, RMS is the most widely used parameters. Except in special circumstances,voltage meter readings almost all carried out by the RMS of sine wave . The reasons of RMS is widely available, on the one hand, because it directly reflects the size of the exchange of signal energy, which the study of power, noise, distortion, spectrum purity, energy conversion, such as it is very important; On the other hand, it has a very simple superposition of the nature of the calculation will be extremely convenient. The design of single-chip Atmel Corporation AT89S52 as control core, by the current sensor module, True RMS measurement modules, signal conditioning modules, AD acquisition and control module, display module. System uses a current sensor circuit for step-down of the input signal processing, has been converted by the original AD736 True RMS signal by the TLC549 convert into single-chip digital conducted after the brief and the results of data processing in real time through the LCD display, achieve a better performance.Keyword: Digital voltage(current) meter True RMS AD736 TLC549AT89S52目录第一章绪论 (1)§1.1 选题背景及意义 (1)§1.2 系统设计任务 (1)第二章系统总体设计 (2)§2.1 方案论证与比较 (2)2.1.1 电压、电流变换部分 (2)2.1.2 有效值测量部分 (2)§2.2 系统总体设计 (2)第三章硬件设计 (4)§3.1 传感器电路设计 (4)3.1.1 电压互感器 (4)3.1.2 电流互感器 (4)§3.2 真有效值转换电路设计 (5)3.2.1 电压、电流切换电路 (5)3.2.2 真有效值测量电路 (6)§3.3 信号调理电路设计 (7)§3.4 A/D转换电路设计 (7)§3.5 单片机及显示电路设计 (9)第四章软件设计 (10)§4.1 LCD1602液晶显示程序 (10)§4.2 A/D转换程序 (10)§4.3 主程序设计 (12)第五章系统调试及误差分析 (13)§5.1 系统调试及测试结果 (13)5.1.1 AD736测试结果 (13)5.1.2 OP07测试结果 (13)5.1.3 TLC549测试结果 (13)5.1.4 工频电压测量精度 (14)5.1.5 工频电流测量精度 (14)§5.2 误差分析 (14)§5.3 改进方法 (15)结束语 (16)致谢 (17)参考文献 (18)附录 (19)附录一完整电路图 (19)附录二程序清单 (20)第一章绪论§1.1 选题背景及意义在日常的生产、生活和科研中，工频电无处不在，所谓工频就是电力供电系统交流电的频率，我国国家规定工频为50赫兹，即周期为0.02秒，英、美等国规定的工频为60赫兹。

ad736原理

ad736原理
AD736是一款专用于测量电压的集成电路。

它是由ADI（Analog Devices
Inc.）公司生产的一款高性能、精确度较高的电压测量芯片。

下面是AD736的工作原理的简要说明：
AD736是一款True
RMS（有效值）电压转换器。

它的主要功能是测量交流电压的有效值，即以电压的平方平均值作为参考。

AD736的输入是交流电压信号，可以是正弦波、方波或其他复杂波形的交流信号。

它通过内部的精确运算放大器将输入信号放大，并通过整流电路将其转换为直流信号。

在转换过程中，AD736内部使用了一个快速响应的四象限乘法器，它将输入信号与一个参考电平相乘，并输出乘积信号。

这个乘积信号经过低通滤波器进行平均，并通过一个精确的校准电路进行调整，以得到准确的有效值输出。

AD736还提供了一个带有输出缓冲器的电流输出，可用于外部电路的连接。

总之，AD736通过精确的电压放大、整流、乘法和滤波等处理，能够准确测量交流电压信号的有效值，并提供相应的输出。

这使得它在许多需要测量电压的应用中得到广泛使用，如功率监测、音频处理、工业自动化等领域。

AD736

REV.CInformation furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.aLow Cost, Low Power,True RMS-to-DC ConverterAD736One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.Tel: 617/329-4700Fax: 617/326-8703FUNCTIONAL BLOCK DIAGRAMFEATURES COMPUTESTrue RMS ValueAverage Rectified Value Absolute ValuePROVIDES200 mV Full-Scale Input Range(Larger Inputs with Input Attenuator)High Input Impedance of 1012 ⍀Low Input Bias Current: 25 pA maxHigh Accuracy: ؎0.3 mV ؎0.3% of ReadingRMS Conversion with Signal Crest Factors Up to 5Wide Power Supply Range: +2.8 V, –3.2 V to ؎16.5 V Low Power: 200 ␮A max Supply Current Buffered Voltage OutputNo External Trims Needed for Specified Accuracy AD737—An Unbuffered Voltage Output Version with Chip Power Down Is Also Available PRODUCT DESCRIPTIONThe AD736 is a low power, precision, monolithic truerms-to-dc converter. It is laser trimmed to provide a maximum error of ±0.3 mV ±0.3% of reading with sine-wave inputs. Fur-thermore, it maintains high accuracy while measuring a wide range of input waveforms, including variable duty cycle pulses and triac (phase) controlled sine waves. The low cost and small physical size of this converter make it suitable for upgrading the performance of non-rms “precision rectifiers” in many applica-tions. Compared to these circuits, the AD736 offers higher ac-curacy at equal or lower cost.The AD736 can compute the rms value of both ac and dc input voltages. It can also be operated ac coupled by adding one ex-ternal capacitor. In this mode, the AD736 can resolve input sig-nal levels of 100 µV rms or less, despite variations intemperature or supply voltage. High accuracy is also maintained for input waveforms with crest factors of 1 to 3. In addition,crest factors as high as 5 can be measured (while introducing only 2.5% additional error) at the 200 mV full-scale input level.The AD736 has its own output buffer amplifier, thereby provid-ing a great deal of design flexibility. Requiring only 200 µA of power supply current, the AD736 is optimized for use in por-table multimeters and other battery powered applications.The AD736 allows the choice of two signal input terminals: a high impedance (1012 Ω) FET input which will directly interface with high Z input attenuators and a low impedance (8 k Ω) inputwhich allows the measurement of 300 mV input levels, while operating from the minimum power supply voltage of +2.8 V,–3.2 V. The two inputs may be used either singly or differentially.The AD736 achieves a 1% of reading error bandwidth exceeding 10 kHz for input amplitudes from 20 mV rms to 200 mV rms while consuming only 1 mW.The AD736 is available in four performance grades. TheAD736J and AD736K grades are rated over the commercial tem-perature range of 0°C to +70°C. The AD736A and AD736B grades are rated over the industrial temperature range of –40°C to +85°C.The AD736 is available in three low-cost, 8-pin packages: plastic mini-DIP, plastic SO and hermetic cerdip.PRODUCT HIGHLIGHTS1.The AD736 is capable of computing the average rectified value, absolute value or true rms value of various input signals.2.Only one external component, an averaging capacitor, is required for the AD736 to perform true rms measurement.3.The low power consumption of 1 mW makes the AD736suitable for many battery powered applications.4.A high input impedance of 1012 Ω eliminates the need for an external buffer when interfacing with input attenuators.5.A low impedance input is available for those applications requiring up to 300 mV rms input signal operating from low power supply voltages.AD736–SPECIFICATIONSREV. C–2–(@ +25؇C ؎5 V supplies, ac coupled with 1 kHz sine-wave input applied unless otherwise noted.)AD736J/A AD736K/BModelConditionsMinTypMaxMinTypMax UnitsTRANSFER FUNCTIONV OUT =Avg .(V IN 2)V OUT =Avg .(V IN 2)CONVERSION ACCURACY 1 kHz Sine Wave Total Error, Internal Trim 1ac Coupled Using C C All Grades0–200 mV rms 0.3/0.30.5/0.50.2/0.20.3/0.3±mV/±% of Reading 200 mV–1 V rms–1.2؎2.0–1.2؎2.0% of Reading T MIN –T MAXA&B Grades @ 200 mV rms 0.7/0.70.5/0.5±mV/±% of Reading J&K Grades @ 200 mV rms 0.0070.007±% of Reading/°C vs. Supply Voltage@ 200 mV rms Input V S = ±5 V to ±16.5 V 0+0.06+0.10+0.06+0.1%/V @ 200 mV rms Input V S = ±5 V to ±3 V 0–0.18–0.30–0.18–0.3%/Vdc Reversal Error, dc Coupled @ 600 mV dc 1.3 2.5 1.3 2.5% of Reading Nonlinearity 2, 0 mV–200 mV @ 100 mV rms 0+0.25+0.35+0.25+0.35% of ReadingTotal Error, External Trim 0–200 mV rms0.1/0.50.1/0.3±mV/±% of Reading ERROR vs. CREST FACTOR 3Crest Factor 1 to 3C AV , C F = 100 µF 0.70.7% Additional Error Crest Factor = 5C AV , C F = 100 µF 2.52.5% Additional ErrorINPUT CHARACTERISTICS High Impedance Input (Pin 2)Signal RangeContinuous rms Level V S = +2.8 V, –3.2 V 200200mV rms Continuous rms Level V S = ±5 V to ±16.5 V 11V rms Peak Transient Input V S = +2.8 V, –3.2 V ؎0.9؎0.9V Peak Transient Input V S = ±5 V ±2.7±2.7V Peak Transient Input V S = ±16.5 V ؎4.0؎4.0V Input Resistance 10121012ΩInput Bias Current V S = ±3 V to ±16.5 V 125125pALow Impedance Input (Pin 1)Signal RangeContinuous rms Level V S = +2.8 V, –3.2 V 300300mV rms Continuous rms Level V S = ±5 V to ±16.5 V llV rms Peak Transient Input V S = +2.8 V, –3.2 V ±1.7±1.7V Peak Transient Input V S = ±5 V ±3.8±3.8V Peak Transient Input V S = ±16.5 V ±11±11V Input Resistance 6.489.6 6.489.6k ΩMaximum Continuous Nondestructive Input All Supply Voltages ±12±12V p-p Input Offset Voltage 4ac Coupled J&K Grades ؎3؎3mV A&B Grades ؎3؎3mV vs. Temperature 830830µV/°C vs. Supply V S = ±5 V to ±16.5 V 5015050150µV/V vs. Supply V S = ±5 V to ±3 V 8080µV/VOUTPUT CHARACTERISTICS Output Offset Voltage J&K Grades ±0.1؎0.5±0.1؎0.3mV A&B Grades ؎0.5؎0.3mV vs.Temperature 120120µV/°C vs. Supply V S = ±5 V to ±16.5 V5013050130µV/V V S = ±5 V to ±3 V5050µV/V Output Voltage Swing 2 k Ω Load V S = +2.8 V, –3.2 V 0 to +1.6+1.70 to +1.6+1.7V 2 k Ω Load V S = ±5 V 0 to +3.6+3.80 to +3.6+3.8V 2 k Ω Load V S = ±16.5 V 0 to +4+50 to +4+5V No Load V S = ±16.5 V 0 to +4+120 to +4+12V Output Current22mA Short-Circuit Current 33mA Output Resistance @ dc 0.20.2ΩFREQUENCY RESPONSE High Impedance Input (Pin 2)For 1% Additional Error Sine-Wave Input V IN = 1 mV rms 11kHz V IN = 10 mV rms 66kHz V IN = 100 mV rms 3737kHz V IN = 200 mV rms3333kHzAD736REV. C –3–AD736J/A AD736K/BModelConditionsMinTypMaxMinTypMaxUnits±3 dB Bandwidth Sine-Wave InputV IN = 1 mV rms 55kHz V IN = 10 mV rms 5555kHz V IN = 100 mV rms 170170kHz V IN = 200 mV rms190190kHzFREQUENCY RESPONSE Low Impedance Input (Pin 1)For 1% Additional Error Sine-Wave Input V IN = 1 mV rms 11kHz V IN = 10 mV rms 66kHz V IN = 100 mV rms 9090kHz V IN = 200 mV rms 9090kHz ±3 dB Bandwidth Sine-Wave Input V IN = l mV rms 55kHz V IN = 10 mV rms 5555kHz V IN = 100 mV rms 350350kHz V IN = 200 mV rms 460460kHz POWER SUPPLYOperatingVoltageRange +2.8, –3.2±5±16.5+2.8, –3.2±5±16.5Volts Quiescent CurrentZero Signal160200160200µA 200 mV rms, No Load Sine-Wave Input230270230270µATEMPERATURE RANGE Operating, Rated Performance Commercial (0°C to +70°C)AD736J AD736K Industrial (–40°C to +85°C)AD736A AD736BNOTES lAccuracy is specified with the AD736 connected as shown in Figure 16 with capacitor C C .2Nonlinearity is defined as the maximum deviation (in percent error) from a straight line connecting the readings at 0 and 200 mV rms. Output offset voltage is adjusted to zero.3Error vs. Crest Factor is specified as additional error for a 200 mV rms signal. C.F. = V PEAK /V rms.4DC offset does not limit ac resolution.Specifications are subject to change without notice.Specifications shown in boldface are tested on all production units at final electrical test.Results from those tests are used to calculate outgoing quality levels.ABSOLUTE MAXIMUM RATINGS 1Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .±16.5 V Internal Power Dissipation 2 . . . . . . . . . . . . . . . . . . . . .200 mW Input Voltage . . . . . . . . . . . . . . . . . . . . . . . ±V S Output Short-Circuit Duration . . . . . . . . . . . . . . . . .Indefinite Differential Input Voltage . . . . . . . . . . . . . . . . .. +V S and –V S Storage Temperature Range (Q) . . . . . . –65°C to +150°C Storage Temperature Range (N, R) . . . . . –65°C to +125°C Operating Temperature RangeAD736J/K . . . . . . . . . . . . . . . . . . . . . . . . . . .0°C to +70°C AD736A/B . . . . . . . . . . . . . . . . . . . . . . . . . .–40°C to +85°CORDERING GUIDETemperature Package Package ModelRange Description Option AD736JN 0°C to +70°C Plastic Mini-DIP N-8AD736KN 0°C to +70°C Plastic Mini-DIP N-8AD736JR 0°C to +70°C Plastic SOIC SO-8AD736KR 0°C to +70°C Plastic SOIC SO-8AD736AQ –40°C to +85°C Cerdip Q-8AD736BQ–40°C to +85°C CerdipQ-8AD736JR-REEL 0°C to +70°C Plastic SOIC SO-8AD736JR-REEL-70°C to +70°C Plastic SOIC SO-8AD736KR-REEL 0°C to +70°C Plastic SOIC SO-8AD736KR-REEL-70°C to +70°CPlastic SOICSO-8PIN CONFIGURATION8-Pin Mini-DIP (N-8), 8-Pin SOIC (R-8),8-Pin Cerdip (Q-8)Lead Temperature Range (Soldering 60 sec) . . . . . . . .+300°C ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .500 VNOTES 1Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability .28-Pin Plastic Package: θJA = 165°C/W 8-Pin Cerdip Package: θJA = 110°C/W8-Pin Small Outline Package: θJA = 155°C/WAD736REV. C–4––Typical CharacteristicsFigure 2.Maximum Input Levelvs. SupplyVoltage Figure 5.Frequency ResponseDriving Pin 2Figure 8.DC Supply Current vs.RMS lnput LevelFigure 1.Additional Error vs.Supply VoltageFigure 4.Frequency ResponseDriving Pin 1Figure 7.Additional Error vs.Temperature Figure 3.Peak Buffer Output vs.Supply VoltageFigure 6.Additional Error vs.Crest Factor vs. CAVFigure 9.–3 dB Frequency vs.RMS Input Level (Pin2)AD736REV. C –5–Typical Characteristics–Figure 10.Error vs. RMS Input Voltage (Pin 2), Output Buffer Off-set Is Adjusted To ZeroFigure 13.Pin 2 Input Bias Current vs. Supply VoltageCALCULATING SETTLING TIME USING FIGURE 14The graph of Figure 14 may be used to closely approximate the time required for the AD736 to settle when its input level is re-duced in amplitude. The net time required for the rms converter to settle will be the difference between two times extracted from the graph – the initial time minus the final settling time. As an example, consider the following conditions: a 33 µF averaging capacitor, an initial rms input level of 100 mV and a final (re-duced) input level of 1 mV. From Figure 14, the initial settling time (where the 100 mV line intersects the 33 µF line) is around 80 ms.The settling time corresponding to the new or final input level of 1 mV is approximately 8 seconds. Therefore, the net time for the circuit to settle to its new value will be 8 seconds minus 80 ms which is 7.92 seconds. Note that, because of the smooth decay characteristic inherent with a capacitor/diode combina-tion, this is the total settling time to the final value (i.e., not the settling time to 1%, 0.1%, etc., of final value). Also, this graph provides the worst case settling time, since the AD736 will settlevery quickly with increasing input levels.Figure 11. C AV vs. Frequency forSpecified Averaging ErrorFigure 14.Settling Time vs. RMS Input Level for Various Values of CAVFigure 12.RMS Input Level vs.Frequency for Specified Averag-ing ErrorFigure 15.Pin 2 Input Bias Cur-rent vs. TemperatureAD736REV. C–6–Table I. Error Introduced by an Average Responding Circuit When Measuring Common WaveformsWaveform Type Crest Factor True rms ValueAverage Responding % of Reading Error*1 Volt Peak (V PEAK /V rms)Circuit Calibrated to Using Average AmplitudeRead rms Value of Responding CircuitSine Waves Will ReadUndistorted 1.4140.707 V 0.707 V 0%Sine Wave Symmetrical Square Wave 1.00 1.00 V 1.11 V +11.0%Undistorted Triangle Wave 1.730.577 V0.555 V–3.8%GaussianNoise (98% of Peaks <1 V)30.333 V 0.295 V –11.4%Rectangular 20.5 V 0.278 V –44%Pulse Train 100.1 V 0.011 V –89%SCR Waveforms 50% Duty Cycle 20.495 V 0.354 V –28%25% Duty Cycle4.70.212 V0.150 V–30%*%of Reading Error =Average Responding Value –True rmsValueTrue rmsValue×100%TYPES OF AC MEASUREMENTThe AD736 is capable of measuring ac signals by operating as either an average responding or a true rms-to-dc converter. As its name implies, an average responding converter computes the average absolute value of an ac (or ac and dc) voltage or current by full wave rectifying and low-pass filtering the input signal;this will approximate the average. The resulting output, a dc “average” level, is then scaled by adding (or reducing) gain; this scale factor converts the dc average reading to an rms equivalent value for the waveform being measured. For example, the aver-age absolute value of a sine-wave voltage is 0.636 that of V PEAK ;the corresponding rms value is 0.707 times V PEAK . Therefore,for sine-wave voltages, the required scale factor is 1.11 (0.707divided by 0.636).In contrast to measuring the “average” value, true rms measure-ment is a “universal language” among waveforms, allowing the magnitudes of all types of voltage (or current) waveforms to be compared to one another and to dc. RMS is a direct measure of the power or heating value of an ac voltage compared to that of dc: an ac signal of 1 volt rms will produce the same amount of heat in a resistor as a 1 volt dc signal.Mathematically, the rms value of a voltage is defined (using a simplified equation) as:V rms =Avg .(V 2)This involves squaring the signal, taking the average, and then obtaining the square root. True rms converters are “smart recti-fiers”: they provide an accurate rms reading regardless of the type of waveform being measured. However, average responding converters can exhibit very high errors when their input signals deviate from their precalibrated waveform; the magnitude of the error will depend upon the type of waveform being measured.As an example, if an average responding converter is calibrated to measure the rms value of sine-wave voltages, and then is used to measure either symmetrical square waves or dc voltages, the converter will have a computational error 11% (of reading)higher than the true rms value (see Table I).AD736 THEORY OF OPERATIONAs shown by Figure 16, the AD736 has five functional subsec-tions: input amplifier, full-wave rectifier, rms core, output am-plifier and bias sections. The FET input amplifier allows both a high impedance, buffered input (Pin 2) or a low imped-ance, wide-dynamic-range input (Pin 1). The high impedance input, with its low input bias current, is well suited for use with high impedance input attenuators.The output of the input amplifier drives a full wave precision rectifier, which in turn, drives the rms core. It is in the core that the essential rms operations of squaring, averaging and square rooting are performed, using an external averaging capacitor,C AV . Without C AV , the rectified input signal travels through the core unprocessed, as is done with the average responding con-nection (Figure 17).A final subsection, an output amplifier, buffers the output from the core and also allows optional low-pass filtering to be per-formed via external capacitor, C F , connected across the feed-back path of the amplifier. In the average respondingconnection, this is where all of the averaging is carried out. In the rms circuit, this additional filtering stage helps reduce any output ripple which was not removed by the averaging capaci-tor, C AV .Figure 16.AD736 True RMS CircuitAD736REV. C–7–As shown, the dc error is the difference between the average of the output signal (when all the ripple in the output has been removed by external filtering) and the ideal dc output. The dc error component is therefore set solely by the value of averaging capacitor used-no amount of post filtering (i.e., using a very large C F) will allow the output voltage to equal its ideal value. The ac error component, an output ripple, may be easily re-moved by using a large enough post filtering capacitor, C F.In most cases, the combined magnitudes of both the dc and ac error components need to be considered when selecting appro-priate values for capacitors C AV and C F. This combined error, representing the maximum uncertainty of the measurement is termed the “averaging error” and is equal to the peak value of the output ripple plus the dc error.As the input frequency increases, both error components de-crease rapidly: if the input frequency doubles, the dc error and ripple reduce to 1/4 and 1/2 their original values, respectively, and rapidly become insignificant.AC MEASUREMENT ACCURACY AND CREST FACTOR The crest factor of the input waveform is often overlooked when determining the accuracy of an ac measurement. Crest factor is defined as the ratio of the peak signal amplitude to the rms am-plitude (C.F. = V PEAK/V rms). Many common waveforms, such as sine and triangle waves, have relatively low crest factors (≤2). Other waveforms, such as low duty cycle pulse trains and SCR waveforms, have high crest factors. These types of waveforms require a long averaging time constant (to average out the long time periods between pulses). Figure 6 shows the additional error vs. crest factor of the AD736 for various values of C AV. SELECTING PRACTICAL VALUES FOR INPUT COUPLING (C C), AVERAGING (C AV) AND FILTERING (C F) CAPACITORSTable II provides practical values of C AV and C F for several common applications.Table II. AD737 Capacitor Selection ChartApplication rms Low Max C AV C F SettlingInput Frequency Crest Time*Level Cutoff Factor to 1%(–3dB)General Purpose0–1 V20 Hz5150 µF10 µF360 msrms Computation200 Hz515 µF 1 µF36 ms0–200 mV20 Hz533 µF10 µF360 ms200 Hz5 3.3 µF 1 µF36 msGeneral Purpose0–1 V20 Hz None33 µF 1.2 secAverage200 Hz None 3.3 µF120 msResponding0–200 mV20 Hz None33 µF 1.2 sec200 Hz None 3.3 µF120 msSCR Waveform0–200 mV50 Hz5100 µF33 µF 1.2 secMeasurement60 Hz582 µF27 µF 1.0 sec0–100 mV50 Hz550 µF33 µF 1.2 sec60 Hz547 µF27 µF 1.0 secAudioApplicationsSpeech0–200 mV300 Hz3 1.5 µF0.5 µF18 msMusic0–100 mV20 Hz10100 µF68 µF 2.4 sec*Settling time is specified over the stated rms input level with the input signal increasingfrom zero. Settling times will be greater for decreasing amplitude input signals.RMS MEASUREMENT – CHOOSING THE OPTIMUMVALUE FOR C AVSince the external averaging capacitor, C AV, “holds” the recti-fied input signal during rms computation, its value directly af-fects the accuracy of the rms measurement, especially at lowfrequencies. Furthermore, because the averaging capacitor ap-pears across a diode in the rms core, the averaging time constantwill increase exponentially as the input signal is reduced. Thismeans that as the input level decreases, errors due to nonidealaveraging will reduce while the time it takes for the circuit tosettle to the new rms level will increase. Therefore, lower inputlevels allow the circuit to perform better (due to increased aver-aging) but increase the waiting time between measurements.Obviously, when selecting C AV, a trade-off between computa-tional accuracy and settling time is required.Figure 17.AD736 Average Responding CircuitRAPID SETTLING TIMES VIA THE AVERAGERESPONDING CONNECTION (FIGURE 17)Because the average responding connection does not use theC AV averaging capacitor, its settling time does not vary with in-put signal level; it is determined solely by the RC time constantof C F and the internal 8 kΩ resistor in the output amplifier’sfeedback path.DC ERROR, OUTPUT RIPPLE, AND AVERAGINGERRORFigure 18 shows the typical output waveform of the AD736 witha sine-wave input applied. As with all real-world devices, theideal output of V OUT = V IN is never exactly achieved; instead,the output contains both a dc and an ac error component.Figure 18. Output Waveform for Sine-Wave Input VoltageAD736REV. C–8–C 1174a –10–9/88P R I N T E D I N U .S .A .The input coupling capacitor, C C , in conjunction with the 8 k Ωinternal input scaling resistor, determine the –3 dB low fre-quency rolloff. This frequency, F L , is equal to:F L =12π(8,000)(TheValue of C C in Farads )Note that at F L , the amplitude error will be approximately–30% (–3 dB) of reading. To reduce this error to 0.5% of read-ing, choose a value of C C that sets F L at one tenth the lowest frequency to be measured.In addition, if the input voltage has more than 100 mV of dc offset, than the ac coupling network shown in Figure 21 should be used in addition to capacitor C C .Applications CircuitsFigure 19.AD736 with a High Impedance Input AttenuatorFigure 20.Differential Input ConnectionFigure 21.External Output V OSAdjustmentFigure 22.Battery Powered OptionFigure 23.Low Z, AC Coupled Input ConnectionOUTLINE DIMENSIONSDimensions shown in inches and (mm).。

AD736在机车信号智能监测中的应用

AD736在机车信号智能监测中的应用
AD736 在机车信号智能监测中的应用
Application of AD936 in Train Signal Intellient Monitoring
铁道科学研究院电子所冯云梅蒋秋华史天运
摘要：对AD736 在机车信号智能监测中的实际应用情况作了详细分析。

关键词：RMS 变换；智能监测；机车信号；轨道感应电压
引言
随着列车运行速度的提升，铁道部规划在未来的列车运行中将逐步取消地面信号机而只使用车上信号系统的重大体制改革，即机车信号系统将是司机操作列车运行的唯一信号引导，而轨道感应电压值的大小直接影响机车信号的正常，所以在对机车信号运行参数的监测中，对轨道感应电压的监测是其中一个很重要的部分。

轨道感应电压是交流小信号，对交流信号有效值的测量主要有以下几种方法：
1）用峰值变换器，通过波峰因数求出有效值；
2）热电偶电桥有效值变换器；
3）用模拟运算组成电子有效值变换器；
4）逐点采样一组数据，求其“均方根”得到其有效值。

以上几种测量方法都存在不同程度的缺点和局限性，为了得到轨道感应电压有效值的精确测量，且实现简单可靠，我们采用真有效值变换器AD736，它通过对输入交流电压进行”平方→求平均值→开平方”的运算而得到交流电压
的有效值。

当我们进行轨道感应电压值的读取时，将变换后的直流信号通过AD 采样器，然后利用单片机进行运算和处理，即可得到感应电压的有效值。

交流有效值—直流变换IC AD736／AD737及应用

交流有效值—直流变换IC AD736／AD737及应用
王俊省;李兰友
【期刊名称】《电子与电脑》
【年(卷),期】1994(000)003
【摘要】AD736用于交流时,需在引脚①(Cc)外接一电容Cc,这时,低频截上频率f_(CL)为f_(CL)=1/(2π·8KΩ·Cc)。

当Cc=10μF时,f_(CH)=2HZ。

四、AD736实用电路——有效值交流电压表使用AD736构成的交流电压表线路如图10所示。

【总页数】1页(P54)
【作者】王俊省;李兰友
【作者单位】不详;不详
【正文语种】中文
【中图分类】TP335.1
【相关文献】
1.基于交流-直流变换的光电式电流有效值传感器+ [J], 李长胜;李宝树;乔冬
2.MAX610系列交流／直流电源变换器的原理和应用 [J], 宋吉江;牛轶霞
3.交流有效值—直流变换IC AD736／AD737及应用 [J], 王俊省;李兰友
4.一种新型的电源变换电路MAX610及其应用（220伏交流变为5V直流电压）[J], 刘强
5.直流变换器AIC1578原理及应用 [J], 邹士洪
因版权原因，仅展示原文概要，查看原文内容请购买。

真有效值转换器AD736及其应用

真有效值转换器AD736及其应用
崔智勇;李建科
【期刊名称】《河北工业大学学报》
【年(卷),期】2005(034)0z1
【摘要】美国AD公司的AD736是一种真有效值转换器电路,它具有准确性高、灵敏度好、测量速率快、频率特性好、输入阻抗高、输出阻抗低、电源范围宽以及功耗低等特点.本文介绍了AD736的工作原理及特点,给出了以该芯片为核心构成的RMS仪表设计电路.
【总页数】3页(P34-36)
【作者】崔智勇;李建科
【作者单位】河北经贸大学,信息技术学院,河北,石家庄,050061;河北经贸大学,信息技术学院,河北,石家庄,050061
【正文语种】中文
【中图分类】TN6
【相关文献】
1.真有效值直流转换器AD536A及其应用 [J], 梁杰
2.真有效值转换器LTC1966的原理与应用 [J], 王彦朋;任文霞;刘勇
3.真有效值 AC/DC转换器 AD736及其在 RMS仪表电路中的应用 [J], 刘春生
4.单片集成型真有效值转芯片AD736的原理及应用 [J], 纪宗南
5.真有效值转换器LTC 1966在电池巡检仪中的应用 [J], 尤文; 谢荣; 姜磊
因版权原因，仅展示原文概要，查看原文内容请购买。

常用电子仪器的使用

注意：量程越小，流过被测电阻的电流越大。量程越大，加在被测电阻上的电压就越大（10K档）。也就是说：不能用万用表测量小功率的小电阻（如毫安表的内阻），不能用万用表R×10K档去测量二级管或三级管的级间电阻。测量完毕不要把量程开关放在欧姆档上，应放在直流电压或交流电压的最大档上或置于空档上。千万注意！！！

基本使用方法： 3.1测试前，首先把万用表放置水平状态，并视其表针是否处于零点（电流、电压的零点），若不在，则应调整表头下方的“机械零位调整”，使指针指向零位。 3.2根据被测项，正确选择万用表上的测量项目及量程开关。
三、万用表的使用

基本使用方法：若已知被测量的数量级，则就选择与其相对应的数量级量程，若不知被测量的数量级，则应从选择最大量程开始测量，当指针偏转角太小而无法精确读数时，再把量程减小，一般以指针偏转角不大于最大刻度的30%为合理量程。（电阻档应以中值电阻附近测量精度最高）
万用表损坏常见现象

指针表电阻档无法测量，电流档、电压档正常。任何电阻均满偏。损坏原因为用电阻档测量AC220V, 造成电阻档取样电阻9.1Ω，91Ω等烧坏。此现象为指针万用表最常见故障。数字万用表测量时每档均乱显示。损坏原因为用电阻档测量AC220V,而该万用表没有设计保护电路造成IC7106损坏。此现象为数字万用表最常见故障。其次为电流200毫安档无法测量，主要为保险管烧坏。故障原因为用低电流档测量大电流。数字万用表完全无显示。主要原因为测量电容时未放电，造成主芯片及外围芯片烧坏
三、万用表的使用

电动系仪表也为交直流两用仪表，使用方法同T10一样。
三、万用表的使用

全国大学生电子设计大赛获奖论文

2012年山东省大学生电子设计竞赛A题低功耗数字多功能表的设计制作低功耗数字多功能表的设计制作摘要：用低功耗单片机为控制核心，设计了低功耗数字多功能表。

本系统包括：直流电压、交流电压、电阻、电容、三极管放大倍数的测量和正弦波信号源电路。

为了提高测量精度，在信号源、电阻、交流电压三个测量电路中，用OPA2111精密仪器放大器芯片，设计了自动较零型仪器放大器。

交流电压信号处理电路中，采用了AD736交流变直流芯片，测量精度较高。

按照题目要求完成了全部功能，并自由发挥增加了晶体管PN结电压的测量功能及温度测量功能。

仿真结果和试验数据表明，本系统具有较高的测量精度，再加后期研发完善，可推广作为数字万用表使用。

关键词：数字多功能表，低功耗，高精度，单片机控制Abstract: With low power consumption single-chip microcomputer as control core, design the low power consumption digital multi-function table. This system includes: dc volts, ac voltage, resistance, capacitance, triode magnification factor measurement and sine wave signal source circuit. In order to improve the measurement precision, the signal source, resistance, ac voltage three in the measurement circuit, with OPA2111 precision instrument amplifier chip, design the automatic a zero type instrument amplifier. In the ac voltage signal processing circuit, adopted AD736 ac variable dc chip, has high accuracy. According to the topic request completed all function, and free play to increase the diode and triode p-n junction voltage measurement function. The simulation results and test data show that this system has high measurement precision, add later research and perfect, can be generalized as digital multimeter use.Keywords: digital multi-function table, low power consumption, high precision, single-chip microcomputer control目录1.方案选择及论证 (3)1.1方案选择 (3)1.2设计方案 (3)2.硬件电路设计及理论分析计算 (3)2.1低功耗供电系统电路 (3)2.2直流电压测量电路 (4)2.3交流电压测量电路 (4)2.4电阻测量电路 (5)2.5电容测量电路 (5)2.6三极管放大倍数测量电路 (6)2.7正弦波信号源电路 (6)3系统软件设计 (7)3.1主程序流程图 (7)3.2系统自动休眠设计 (7)4.测试方案和测试结果分析 (7)4.1直流电压测量方法和测试结果 (7)4.2交流电压测量方法和测试结果 (7)4.3电阻测量方法和测试结果 (8)4.4电容测量方法和测试结果 (8)4.5三极管放大倍数测量方法和测试结果 (8)4.6正弦波信号源测量方法和测试结果 (8)4.7晶体管PN结电压测量方法和测试结果 (9)5自由发挥部分 (9)5.1测晶体管PN结电压电路 (9)5.2温度测量电路 (9)6结论 (9)参考文献 (10)附录1：系统电路原理总图 (11)附录2：部分程序清单 (12)1.方案选择及论证1.1 方案选择方案一：选用MSP430单片机为控制核心。

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真有效值AC/DC转换器AD736及其在RMS仪表电路中的应用
1 概述
在科学实际和生产实践中，会遇到大量的非正弦波。

传统测量仪表采用的是平均值转换法来对其进行测量，但这种方法存在着较大的理论误差。

为了实现对交流信号电压有效值的精密测量，并使之不受被测波形的限制，可以采用真有效值转换技术，即不通过平均折算而是直接将交流信号的有效值按比例转换为直流信号。

为了适应现代电子测量的需要，目前测量交流电压真有效值（RMS）的万用表得到了迅速的发展。

交流电压的真有效值是通过电路对输入交流电压进行“平方→求平均值→开平方”的运算而得到的。

真有效值仪表的最大优点是能够精确测量各种电压波形的有效值，而不必考虑被测波形的参数以及失真。

随着集成电路的迅速发展，近年来出现了各种真有效值 AC/DC转换器。

美国AD公司的AD736是其中非常典型的一种。

AD736是经过激光修正的单片精密真有效值AC/DC转换器。

其主要特点是准确度高、灵敏性好（满量程为200mVRMS）、测量速率快、频率特性好（工作频率范围可达0～460kHz）、输入阻抗高、输出阻抗低、电源范围宽且功耗低最大的电源工作电流为200μA.用它来测量正弦波电压的综合误差不超过±3%.
2 工作原理及管脚功能
AD736 的内部框图。

它主要由输入放大器、全波整流器、有效值单元（又称有效值芯子RMS CORE）、偏置电路、输出放大器等组成。

芯片的2脚为被测信号VIN输入端，工作时，被测信号电压加到输入放大器的同相输入端，而输出电压经全波整流后送到RMS单元并将其转换成代表真有效值的直流电压，然后再通过输出放大器的Vo端输出。

偏置电路的作用是为芯片内部各单元电路提供合适的偏置电压。

AD736采用双列直插式8脚封装，其管脚排列。

各管脚的功能如下：
+Vs：正电源端，电压范围为2.8～16.5V；
-Vs：负电源端，电压范围为-3.2～-16.5V；
Cc：低阻抗输入端，用于外接低阻抗的输入电压（≤200mV），通常被测电压需经耦合电容Cc与此端相连，通常Cc的取值范围为10～20μF.当此端作为输入端时，第2脚VIN 应接到COM；
VIN：高阻抗输入端，适合于接高阻抗输入电压，一般以分压器作为输入级，分压器的总输入电阻可选10MΩ，以减少对被测电压的分流。

该端有两种工作方式可选择：第一种为输出AC+DC方式。

该方式将1脚（Cc）与8脚（COM）短接，其输出电压为效流真有效值与直流分量之和；第二种方式为AC方式。

该方式是将1脚经隔直电容Cc接至8脚，这种方式的输出电压为真有效值，它不包含直流分量。

COM：公共端；
Vo：输出端；
CF：输出端滤波电容，一般取10μF；
CAV：平均电容。

它是AD736的关键外围元件，用于进行平均值运算。

其大小将直接响应到有效值的测量精度，尤其在低频时更为重要。

多数情况下可选33μF.
3 典型应用电路
AD736 有多种应用电路形式。

图3为双电源供电时的典型应用电路，该电路中的+Vs与COM、-Vs与COM之间均应并联一只0.1μF的电容以便滤掉该电路中的高频干扰。

Cc起隔直作用。

若按图中虚线方向将1脚与8脚短接而使Cc失效，则所选择的就是AC+DC方式；去
掉短路线，即为AC方式。

R为限流电阻， D1、D2为双向限幅二极管，超过压保护作用，可选IN4148高速开关二极管。

图4为采用9V电池的供电电路。

R1、R2为均衡电阻，通过它们可使VCOM=E/2=4.5V.C1、C2为电源滤波电容。

上述图3和图4电路均为高阻抗输入方式，适合于接高阻抗的分压器。

图5和图6分别为低阻抗输入方式时，用双电源供电和采用9V单电源供电时的典型应用电路。

4 注意事项
图7是由AD736构成的简单RMS仪表组成框图。

图8是由单片机8098和AD736等芯片组成的可测量交直流有效值的智能化RMA仪表组成框图。

应用AD736来制作RMS仪表时，应注意以下几个问题：
（1）当被测交流电压超过200mVRMS时，必须在AD736前加一级分压器，以将被测电压衰减到200mV以内。

在采用
AD736典型电路制作RMS仪表时，可在AD736的输出端接1.0级、200mV直流毫伏表，或接3位半数字电压表（DVM）。

也可利用典型的500型万用表的直流电压档，加上AD736的典型应用电路改制成RMS仪表，AD736应用电路的电源可取自万用表内的9V电池。

（2）若要测量交流电流的真有效值，应在AD736前面加一级分流器。

此时应用AD736可选图6所示电路。

（3）设计高精度真有效值RMS时，还应考虑被测电压的波峰因素Kp（波峰因数Kp是被测信号的峰值与真有效值之比）的影响，应仔细选择合适的CAV.常见的正弦波、言波、三角波和锯齿波的Kp≤2，此时CAV可取33μF.但对于窄脉冲或晶闸管的波形，由于Kp>2，因此应适当增大CAV的容量，以延长取平均值的时间，从而减少由Kp>2所引起的附加误差。