恒流源在高精度数字多用表中的设计与实现外文翻译

1、附录1英文参考资料The con sta nt curre nt source in high precisi on digital desig n and impleme ntatio n of multiple tablesThe constant current source in instrumentation, electronic equipment and high-tech scie nee and tech no logy is an importa nt comp onent of. In high precisi on digital multimeter, has th

2、e basic function of the resistance measurement, and the method of resistance measurement is usually through a resistance voltage (R-U) conv ersi on circuit, which adopts the method of con sta nt curre nt source.Precision constant current source resistance measurement accuracy depends largely on the

3、flow through the measured resista nce, whe n the con sta nt curre nt source with high accuracy, stable voltage measured resista nce, can improve the measureme nt accuracy of resista nce. Therefore, the desig n of a good stability, high accuracy of the constant current source is very important. Accor

4、ding to the actual needs, in the device select ion, con sideri ng the in flue nce of no ise, Wen Piao, desig n aeon sta nt curre nt source with good stability.1 con sta nt curre nt source is in troducedThe basic function of a constant current source is to eliminate or reduce the power supply voltage

5、,load resista nce and the in flue nce of en vir onmen tal temperature on the output current. The constant current source according to the adjustment of differe nt ways, can be divided into direct and in directadjustme nt of con sta nt curre nt source adjustable constant current source. Direct adjust

6、ing typeconstant current source circuit is simple, the main power supply and constant current devices, using the nonlinear characteristic of constant current devices are used to directly adjust the load current.For example, a constant current diode, but its current value is limited and stability is

7、poor. The in direct adjustme nt is a con sta nt curre nt circuit composed of electro nic tubes, tran sistors and other electro nic comp onents together constitute the. For example, feedback OP amplifier based onconstant current source, the use of such circuit can produce excellent performance consta

8、ntcurrent source.1.1 basic structure feedback con sta nt curre nt sourceFeedback constant current source through the negative feedback effect, to make comparis on betwee n the amplifier two in put voltage are equal, so as to mai nta in a constant output current. This circuit is connected in series w

9、ith the load change on the adjustment of the change of resistance to compensate theoutput current, so it is also called the series adjustable constant current source. Itmainly consists of a refere nce voltage source, a comparis on amplifier, adjust the sampli ng resista nee pipe, and other parts. Sp

10、ecific work process: through the sampli ng resistor to the output curre nt in to a voltage feedback amplifier in put, to compare, in comparis on with the refere nee voltage, the voltage error amplifier amplified to con trol the resista nee adjusti ng pipe to adjust the output curre nt, maintain con

11、sta nt output curre nt.1.2 basic circuit modelThere are many specific forms of feedback circuit of constant current source, accordi ng to the loadc onn ecti on mode of con sta nt curre nt source, divided into load grounding type and load of float in gtype, because of the con sta nt curre nt source i

12、s designed for the application of digital multiresistanee measurementfunction in the table, and the digital multimeter in measuring electric wirewhen the black pen and sheet resista nee digital multimeter internal circuit board is conn ected, so the measured load resista nee at one end is groun ded,

13、 so the desig n of the eon sta nt curre nt sourceshould be groun ded load type.2 eon sta nt curre nt source circuit desig nOn the basis of the design of high precision digital multi funetion meter measuri ng resistor, the resista nee profile of differe nt n eeds of differe nt eon sta nt curre nt sou

14、rce, and therefore n eed to desig n a 4 eon sta n curre nt output of the eon sta nt curre nt source circuit. Comb ined with the desig n of feedback eon sta nt curre nt source prin ciple, by differe nt sampli ng resista nee value, so as to achieve 4 differe nt eon sta nt curre nt source output.In the

15、 desig n of eon sta nt curre nt source, a refere nee voltage select ion is very important, it directly affects the stability of the constant current source. The referenee voltage requirements of high precision, small temperature drift, need to choose the referenee voltage chip with low noiseBased on

16、 the above requireme nts, eon sideri ng the choice of Lin ear Tech no logy Corporation shunt voltage referenee chip LM399, typical output voltage referenee value 6.95V. It has the following characteristics: drift coefficient, 0.5ppm/ C; dyn amic resista nee is small, the maximum of 1 ohm ;no ise vol

17、tage effective value of maximum 20 V in itial accuracy of 2%.LM399 internal thermostatic heater, can improve the effect of temperature drift, stable performanee for a long time. The constant current source circuit in the amplifier offset voltage, temperature drift ,no ise voltage will affect the acc

18、uracy of the eon sta nt curre nt source, so the error amplifier should have high in put impeda nee, low no ise and low leakage curre nt. Based on the above eon siderati on s,the desig n uses the ADI compa ny AD706, two operati onal amplifiers with intern al. It is a bipolar field effect tran sistor

19、(BiFET) of the in put stage, so it has high in put impeda nee, low in put bias current,low offset voltage, low offset voltage drift, low power consumption etc.Select the JFET to replace the tran sistor regulator, voltage con trolled eleme nt is JFET. A transistor is a current control device, it will

20、 introduce the base current to constant current source output, in a small constant current source output error, gate level JFET no current flows, so the effect ofconstant current source than the tran sistor effect of small, con sta nt curre nt source can obta in small error.The whole circuit design

21、can have 4 different constant current source output curre nt, output curre ntsampli ng resistor switchi ng con sta nt curre nt source by choos ing different. The circuit is divided into two parts, the first part is composed of LM399, U201A, JFET and Q201. The amplifier constant current receiver; the

22、 seco nd part is JFET Q202, Op U201B(R5,R6,sampli ng resista nce,R7,R8)aco nsta nt curre nt output curre nt source circuit.In summary, in view of the high precisi on digital versatile resista nee measurement function in the table, the design of the constant current source with high stability. Throug

23、h the an alysis of a typicalc on sta nt curre nt source circuit structure and working principle, some key factors which have impact on the accuracy of the constant current source, puts forward the design scheme of the constant current source, the scheme adopts the feedback circuit composed of operat

24、i onal amplifier with low noise to the design, the hardware principle diagram and give con crete. The experime ntal results show that: the desig n of the con sta nt curre nt source can meet the high precision digital multimeterresistanee measurement function application. The circuit has small volume

25、 and high reliability,flexible design, has a good value.附录2译文恒流源在高精度数字多用表中的设计与实现恒流源在仪器仪表、电子设备及高新科学技术中属于一个重要的部件。在 高精度的数字多用表中，具有基本的电阻测量功能，而电阻测量的方法通常是经 过电阻一电压（R-U）转换电路，即采用恒流源的方法。电阻的测量精度很大程度上取决于流过该被测电阻的恒流源电流的精度，当恒流源电流精度高时，测得电阻的电压稳定，能够提高电阻的测量精度。因此,设计一个稳定性好、 准确度高的恒流源是十分关键。本文根据实际的需要，在 器件选型上，考虑到噪声、温漂的影响，设计出

26、稳定性好的恒流源。1恒流源介绍恒流源的基本作用是消除或消弱电源电压、负载电阻和环境温度变化对输出电流的影响。恒流源按照调整方式的不同，可以分为直接调整型恒流源和间接调 整型恒流源。直接调整型恒流源电路简单，主要有供电电源和恒流器件构成，利 用了恒流器件的非线性特性对负载电流进行直接的调整。例如恒流二极管，但其电流值有限且稳定度也较差。间接调整型是由电子管、晶体管和其他电子元件一起构成的恒流电路。例如基于0P放大器的反馈型恒流源，利用此类电路可以 制作出性能优良的恒流源。1.1反馈型恒流源基本结构反馈型恒流源是通过负反馈的作用，使加到比较放大器的两个输入端电压相 等，从而保持输出电流恒定。这种电

27、路是依靠与负载串联的调整管的内阻变化来补偿输出电流的变化，故又称为串联调整型恒流源。它主要由基准电压源、比 较放大器、调整管、采样电阻等部分构成。具体的工作过程：通过采样电阻把输 出电流转变成电压，反馈给比较放大器输入端，在与基准电压相比较，放大器把 误差电压放大后去控制调整管的内阻对输出电流进行调整，维持输出电流恒定。1.2基本电路模型反馈型恒流源的具体电路形式有很多，根据恒流源的负载连接方式不同，分 为负载接地型和负载浮制型，由于所设计的恒流源是针对数字多用表中的电阻测 量功能的应用，而数字多用表在测量电阻时其中黑表笔端与数字多用表内部电路 板的地线相连，因而所测负载电阻有一端是接地的，

28、故所设计的恒流源应是负载 接地型的。2恒流源电路设计依据所设计的高精度数字多用表的电阻测量功能，不同的电阻档需要不同的恒流源电流，因而需设计一个有4种恒定电流输出的恒流源电路。设计结合反馈型恒流源基本工作原理，通过选择不同的采样电阻值，从而达到4路不同的恒流 源电流输出。在恒流源的设计中，基准电压的选择十分重要，它直接影响着恒流源的稳定 性能。基准电压要求精度高，温漂影响小，需要选择低噪声的基准电压芯片。基于以上的要求，综合考虑后选择了凌特公司的并联电压参考芯片 LM399, 输出基准电压的典型值为6.95V。它具有以下特点：温漂系数小，0.5ppm/ C； 动态电阻小，最大1 Q;噪声电压有

29、效值最大20卩V;初始精度2%LM399内部自带恒温加热器，能够改善温度漂移带来的影响，长期的稳定性 能好。其恒流源电路中的运放的失调电压、温漂、噪声电压等会影响恒流源电流的精度，因此误差比较放大器应该具有高输入阻抗、低噪声和超低漏电流。基于以上考虑，设计采用 ADI公司的AD706,内部含有两个运算放大器。它是 具有双极性场效应晶体管(BiFET)的输入级，因此具有高的输入阻抗、低输入偏置电流，低失调电压，低失调电压温漂，低功耗等特点。调整管选择JFET替代了晶体管，JFET是压控型元件。晶体管是电流控制 型器件，它的基极电流会引入到恒流源电流输出端，在小电流恒流源输出时误差影响大，JFET

30、的栅级没有电流流入，故对恒流源电流的影响远比晶体管的影响 小，可以获得误差极小的恒流源。所设计的整体电路可以有4路不同的恒流源电流输出，通过选择不同的采样 电阻来切换恒流源的输出电流。电路分两部分，第一部分由LM399、运放U201A、 JFET Q201等构成恒流接收器；第二部分有运放 U201B JFET Q202、采样电 阻(R5,R6,R7,R8)等构成恒流源电流输出电路。综上所述，针对高精度数字多用表中的电阻测量功能，设计了一种高稳定度 的恒流源。通过分析典型的恒流源的电路结构和工作原理，研究了影响恒流源精度的一些关键因素，提出了恒流源的设计方案，该方案采用由低噪声的运算放大 器构成

31、的反馈型电路来设计，给出了具体的硬件原理图。实验结果表明：设计的 恒流源能够满足高精度的数字多用表中电阻测量功能应用。该电路具有较小的体积和高可靠性，设计方式灵活，具有很好的使用价值。目录错误！未定义书签错误！未定义书签1 总论1.1项目概况1.2建设单位概况错误！未定义书签1.3项目提出的理由与过程 错误！未定义书签1.4可行性研究报告编制依据错误！未定义书签1.5可行性研究报告编制原则错误！未定义书签1.6可行性研究范围 错误！未定义书签1.7结论与建议 错误！未定义书签2项目建设背景和必要性 错误！未定义书签2.1项目区基本状况 错误！未定义书签2.2项目背景 错误！未定义书签2.3项目建设的必要性 错误！未定义书签3市场分析 错误！未定义书签3.1物流园区的发展概况 错误！未定义书签3.2市场供求现状 错误！未定义书签3.3目标市场定位 错误！未定义书签3.4市场竞争力分析 错误！未定义书签4项目选址和建设条件 错误！未定义书签4.1选址原则 错误！未定义书签4.2项目选址 错误！未定义书签4.3场址所在位置现状 错误！未定义书签4.4建设条件 错误！未定义书签5主要功能和建设规模 错误！未定义书签5.1主要功能 错误！未定义书签5.2建设规模及内容 错误！未定义书签6工程建设方案 错误！未定义书签6.1设计依据 错误！