更好测量电阻的9个提示，by Agilent
Tip 1: Removing errors due to lead resistanceMaking 4-wire resistance measurements - The 4-wire ohms method provides the most accurate way to measure small resistances. Test lead resistances and contact resistances are automatically reduced using this method. The connections for resistance measurements are shown below.
4-wire ohm measurement image
Using a known current source and measuring the voltage produced by the resistor the unknown resistance can be calculated.
Removing 2-wire Ohm Test Lead Resistance - For many applications a two-wire measurement will be more than adequate, it is easier to handle two probes, and the measurement is much faster. The Null function can be used to eliminate offset errors associated with the test lead resistance in 2-wire ohms measurements. The first step is to short the two leads together and wait for the DMM to display the resistance of the test leads. The second step is to press the Null button. The meter should now display a reading very close to zero. Each subsequent reading will be the actual resistance measurement minus the initial null measurement (test lead resistance).
Tip 2: Removing errors due to Thermal EMF (often due to leads)
Thermal EMF caused by dissimilar metals can create a parasitic voltage VEMF in the measurement circuit. The additional voltage will create a measurement error, R=(V+ VEMF)/i. Thermoelectric voltages are generated internally in the resistor or when you make circuit connections due to dissimilar metals at different temperatures. Junctions to consider are at the DUT, relay (multiplexers), and to the multimeter. Each metal-to-metal junction forms a thermocouple, which generates a voltage proportional to the junction temperature. Using all copper connections can minimize errors.
Offset compensation can further minimize thermal EMF errors. The diagram below illustrates the two measurements used in offset compensated measurements, one with the current source and a second without the current source.
Offset compesation image
The actual resistance is determined by subtracting the second measurement from the first and dividing by the known current source. When using offset compensation the multimeter will make the two measurements and report just the compensated resistance. Offset compensation can be used in both two and four-wire measurements. Using offset compensation will improve measurement accuracy but will reduce measurement speed.
Tip 3: Removing internal error, often due to thermal EMF
Autozero is used to remove sources of error within the multimeter. When autozero is enabled the multimeter internally disconnects the input signal following each measurement, and takes a zero reading. It then subtracts the zero reading from the preceding reading. This prevents offset voltages present on the multimeter's input circuitry from affecting measurement accuracy. Autozero is always enabled for four-wire measurements but can be disabled for two-wire measurements.
When autozero is disabled, the multimeter takes one zero reading and subtracts it from all subsequent measurements. It takes a new zero reading each time you change the function, range, or integration time.
Tip 4: Power dissipation effects
When measuring resistors designed for temperature measurements or other resistive devices that vary with temperature, be aware that the meter will dissipate some power in the device-under-test. The effects of this power dissipation can affect the measurement accuracy.
If power dissipation is a problem, you can select a higher measurement range, one which uses a lower current source thus reducing the self-heating. Some multimeters, such as the 34420A offer a low power setting. Using the low power setting or a higher resistance range requires a multimeter with good resolution. Below is a table showing the power dissipated by a resister by range and how a low-power setting can reduce the power.
Normal Normal Low Power Low Power Range Test Current DUT Power at Full Scale Test Current DUT Power at Full Scale 1Ω 10 mA 100 µW 10 mA 100 µW 10Ω 10 mA 1 mW 10 mA 1 mW 100Ω 10 mA 10 mW 1 mA 100 µW 1kΩ 1 mA 1 mW 100 µA 10 µW 10kΩ 100 µA 100 µW 10 µA 1 µW 100kΩ 10 µA 10 µW 5 µA 2.5 µW 1MΩ 5 µA 25 µW 5 µA 25 µW
Tip 5: Output Voltage Clamping
Resistance measurements on certain types of contacts may require a limitation on the voltage applied to the material during a resistance measurement. Both the voltage used to make the measurement and the open circuit voltage should be considered. The need for voltage limitation arises from the possibility that oxidation on the contact surfaces may increase the resistance reading. If the voltage is too high, the oxide layer may be punctured resulting in a lower resistance reading. Not all DMMs offer built-in voltage clamping circuits.
An example of a multimeter that offers a voltage clamping circuit is the 34420A. The 34420A provides a programmable level of open circuit clamping. The voltage-limited measurement is available on the 10 and 100 ohm ranges. The open circuit voltage and measurement voltage can be clamped at one of three levels, 20 mV, 100 mV, or 500 mV.
Range Test Current Measurement Voltage (Full Scale) Open Circuit Voltage (Full Scale) 10Ω 1 mA 10 mV 20, 100, or 500 mV 100Ω 0.1 mA 10 mV 20, 100, or 500 mV
Tip 6: Settling time Effects
Modern multimeters have the ability to insert automatic measurement settling delays. These delays are adequate for resistance measurements with less than 200 pF of combined cable and device capacitance. This is particularly important if you are measuring resistances above 100 kΩ. Settling due to RC time constant effects can be quite long. Some precision resistors and multi-function calibrators use large parallel capacitors (1000 pF to 0.1 mF) with high resistor values to filter out noise currents injected by their internal circuitry. Non-ideal capacitances due to dielectric absorption (soak) effects in cables and other devices may have much longer settling times than expected just by RC time constants. Errors will be measured when settling after the initial connection and after a range change. You may need to increase the delay time before a measurement in these situations. The amount of delay can typically be set from the front panel or programmatically.
Tip 7: Errors in High Resistance Measurements
When you are measuring large resistances, significant errors can occur due to insulation resistance and surface cleanliness. You should take the necessary precautions to maintain a "clean" high-resistance system. Test leads and fixtures are susceptible to leakage due to moisture absorption in insulating materials and "dirty" surface films. Nylon and PVC are relatively poor insulators (109 ohms) when compared to PTFE Teflon ® insulators (1013 ohms). Leakage from nylon or PVC insulators can easily contribute a 0.1% error when measuring a 1 MΩ resistance in humid conditions.
Tip 8: Continuity Test
The Agilent 34401A multimeter offers continuity test, a quick way to determine if a resistance is below a given threshold. When measuring continuity, the multimeter emits a continuous tone if the measured resistance is less than the threshold resistance. The continuity test is performed on a fixed range 1kΩ (1mA current source) and is made with 5½ digits of resolution. The default threshold resistance is 10 ohms but can be changed from 1 to 1000 ohms. It is important to note, that the threshold value can only be set from the front panel and is stored in non-volatile memory. The threshold resistance is not affected by power being removed or a reset command being received. The "BEEPER ON/OFF" control does not affect the continuity tone, which is always enabled.
The 34401A also offers a Diode Test while not a pure resistance measurement it uses the same hardware, a 1 mA current source and the resulting voltage measured on the 1Vdc range. The beeper will indicate a forward biased diode the measured voltage needs to be equal to or greater than .3 Volts but less than or equal to .8 Volts. The threshold is not adjustable but the beeper can be enabled or disabled (BEEPER ON/OFF).
Math functions such as null, limit, and statistics cannot be used in combination with the continuity or diode test.
Tip 9: Accessories to make better resistance measurements
Agilent offers several accessories to make better resistance measurements; often the leads are built from the same material as the multimeter connectors to avoid thermal EMF errors. Another consideration is that connection is made with reasonable pressure, to insure a good fit.
Kelvin Probe sets, feature a spring-loaded clip allow the source and sense leads to be connected simultaneously to the DUT. 11059A Kelvin Probe Set features gold plated clips and works with both the 34401A and 3458A. You can build your own custom lead set with the 11062A Kelvin Clip Set Deluxe Lead Set, offer several needle and alligator style clips. The 34132B Deluxe Lead Set with Retractable Sheath can be used with both the 34401A and the 3458A. The 34132A Fixed Sheath Deluxe Lead set is designed just for the 34401A and offers a better fit at the multimeter. For the ultimate in stable connections we offer spade lug connections for the 3458A; 11053A Low Thermal EMF Lug-to-Lug Jumper Set and the 11174A Low Thermal EMF Lug-to-Banana Jumper Set. For the 34420A we offer a specially designed low-thermal mating connector 34104A and the 34102 low-thermal input cable. Shorting blocks can be used to make a null measurement. They are also used during calibration. The 34172A DMM Calibration Short is specifically designed for the 34401A using the same metal as the input connector, as well as providing insulation from moving air. The Agilent 34103A is a low-thermal shorting plug for the34420A. It provides a convenient and reliable short. One ships with the 34420A. 好资料，能翻译成中文就好了！ 楼主没附图，怎么用 Offset compensation 抵消热电势的影响？
另外，第六条指的是表内电流源的建立时间，还是外部测试线缆，甚至是被测电阻本身的电容？
此外，我一直对第 4 条有一个问题，就是表的电流源是否是可靠的，电流源依靠表内参考电阻还是什么电阻建立？这个电流流过表内这个电阻，这个电阻是否也会发热而最终导致表提供的电流变化呢？我发现 6871 测试一个 10K 电阻，刚接上去得到的测试结果和一段时间后相比，大 3ppm 这样；用 3547A 串联在电流通路中，发现这个电流确实从刚接上去开始逐渐下降了 3ppm，这是正常情况，还是表有问题了？ 借助Google
提示1：消除导线电阻引起的误差
制作4线电阻测量 - 4线欧姆方法提供了最准确的方法来测量小电阻。测试引线电阻和接触电阻会自动减少使用这种方法。用于电阻测量的连接如下。
4线欧姆测量形象
使用一个已知的电流源和测量未知电阻的可以计算出电阻产生的电压。
取消对许多应用2线欧姆测试线电阻 - 两线测量会较充足，更是容易处理两个探头，测量快得多。空函数可用于消除抵消了2线欧姆测量测试引线电阻产生的错误。第一步是要短的两根导线一起等待的万用表显示了测试阻力的线索。第二步是按空按钮。该表显示的阅读现在应该非常接近于零。以后每次阅读将是实际的电阻测量减去初始空测量（测试导线电阻）。
提示2：删除错误由于热电动势（往往因脚）
热电动势所引起的异种金属可以创建一个测量电路中的寄生电压VEMF。这将创建一个额外的电压测量误差，研究=（五+ VEMF）/岛热电电压在内部产生的电阻或当你因电路连接在不同温度下对不同的金属。路口要考虑的是在被测件，继电器（），并万用表多工器。每种金属与金属连接形成一个热电偶，可产生电压成正比的结温。使用全铜连接可以减少错误。
偏移补偿，可进一步减少热电动势的错误。下图说明了两个用于测量偏移补偿测量，电流源和电流源没有第二个。
偏移补偿站形象
实际的阻力是由减去从第一和第二次测量已知的电流源划分。当使用偏移补偿万用表将两次测量和报告的公正性的补偿。偏移补偿既可以用于两个四线测量。使用偏移补偿将提高测量精度，测量速度会降低。
提示3：删除内部错误，往往是由于热电动势
自动归零是用来清除在万用表的误差来源。当启用自动归零万用表内部断开以下每个测量输入信号，并采取零读。然后减去从前面的阅读零读。这可以防止影响测量精度的偏移电压的万用表的输入电路中。自动归零总是启用四线测量，但可以为两线测量禁用。
当自动归零被禁用，需要一零万用表读数和减去所有后续测量它。它需要一个新的零阅读每次更改的功能，范围，或整合时间。
提示4：功率损耗的影响
当测量电阻设计的温度测量或其他电阻随温度变化的设备，都知道，米就会逐渐消失中的某些设备在测试的权力。这一功耗的影响可能会影响测量精度。
如果功耗是一个问题，你可以选择一个更高的测量范围，它使用一个较低的电流源从而降低自身发热。如34420A一些万用表，提供一个低功率设置。使用低功率设置或更高的电阻范围，需要一个良好的决议万用表。下面是一个表显示了一个由电阻消耗的功率范围，以及如何低功耗设置可以降低功耗。
正常的普通低功率低功率
在全部范围测试量表测试DUT的电流DUT的功率电流电源在满量程
1Ω十毫安100微瓦十毫安100微瓦
10Ω十毫安1毫瓦十毫安1毫瓦
100Ω一〇毫安10毫瓦一毫安100微瓦
1kΩ的1毫安1毫瓦100微安10微瓦
10kΩ的100微安100微瓦10微安1微瓦
100kΩ的10μA的10微瓦5μA的2.5微瓦
为1MΩ5μA的25微瓦5μA的25微瓦
提示5：输出电压钳位
对某些类型的接触电阻测量可能需要在应用过程中的材料电阻测量的电压限制。无论是用于制作电压测量和开路电压应予以考虑。为有需要的电压限制可能会增加阻力读取的可能性就接触表面氧化。如果电压过高，氧化层可能被刺破在一个较低的阻力导致阅读。并非所有的DMM提供内置钳位电压电路。
一个万用表，提供了一个电压钳位电路的例子是34420A。该34420A提供了可编程的水平夹紧开路。在电压测量可以用有限的10和100欧姆的范围。开路电压和测量电压可以在三个层次，20毫伏，100毫伏，或500毫伏1钳制。
电压电流测量范围测试（全尺寸）开路电压（满量程）
10Ω1毫安10毫伏20，100或500毫伏
100Ω0.1毫安10毫伏20，100或500毫伏
提示6：建立时间的影响
现代万用表有能力解决拖延插入自动测量。这些延误是电阻测量足够少于200电缆和设备相结合pF的电容。这一点特别重要，如果你是100kΩ的电阻测量以上。解决由于RC时间常数的影响可能相当长。一些精密电阻器，多功能校准器使用大型（1000 pF的电容并联到0.1uF的）高电阻值，筛选出其内部电路噪声电流注入。非理想电容因介质吸收（吸收）的电缆和其他设备的影响可能有更长的时间解决不仅仅是由RC时间常数的预期时间。测量时将错误解决在初始连接后，后一个范围的变化。您可能需要增加在这些情况之前测量的延迟时间。的延迟量通常可以设置前面板或编程。
秘诀7：高电阻测量误差
当您测量大电阻，可能会出现重大错误，由于绝缘电阻和表面清洁。你应该采取必要的预防措施，以保持一个“干净”高电阻系统。测试导线和夹具容易渗漏由于绝缘材料和“脏”的电影，表面水分的吸收。尼龙和PVC相对贫困绝缘体（109欧姆）相比，PTFE特氟龙®绝缘体（1013欧姆）。由尼龙或PVC绝缘子泄漏可以很容易地贡献了0.1％的误差测量时，在潮湿条件1MΩ的电阻。
提示8：连续性测试
安捷伦34401A万用表提供连续性测试，一个快速的方法来确定是否一个电阻低于某一阈值。当测量连续性，万用表发出一个音，如果连续测量电阻小于临界电阻低。测试的连续性上执行一个固定范围的1kΩ（1mA的电流源），并与5 ½位数字作出的决议。默认的阈值是10欧姆的电阻，但可以从1更改为1000欧姆。重要的是要注意到，该阈值只能设置前面板，并在非易失性内存中存储。阈值电阻不受权力被删除或重置命令被接收。该“蜂鸣器开/关”控制不会影响基调的连续性，这是始终启用。
在34401A还提供了一个二极管测试，而不是一个纯电阻测量它使用相同的硬件，1 mA电流源和由此产生的电压范围内测定的1Vdc。蜂鸣器会显示二极管的正向电压测量必须等于或大于0.3伏特，但更大的偏见少大于或等于0.8伏特。阈值是不可调的蜂鸣器，但可以启用或禁用（蜂鸣器开/关）。
数学函数，如无效，限制和统计数据不能用于结合的连续性或二极管测试。
提示9：配件更好地电阻测量
安捷伦提供了多种配件，以更好地电阻测量;往往是从领导的万用表连接器同样的材料建造，以避免热电动势的错误。另一个要考虑的是，连接是用合理的压力，以确保合适。
开尔文探针台，设有一个弹簧式夹允许的来源和意义，同时导致连接到DUT。 11059A Kelvin探针功能与设置都34401A和3458A镀金片段和工程。你可以建立自己的自定义设置与11062A导致夹上开尔文
豪华铅设置，提供了多种针和鳄鱼式剪辑。豪华的34132B与伸缩护套铅可用于设置两个34401A和3458A。豪华的34132A固定铅护套设计一套只为34401A万用表，并提供在更合适。
这在我们提供稳定的连接最终铲耳为3458A的联系; 11053A低热EMF十字对十字跳线设置和11174A低热EMF十字对香蕉跳线设置。对于34420A我们提供了一个特别设计的低热量交配连接器34104A和34102低热量输入电缆。
短路块可以用来制造一个空的测量。它们还用于在校准。在34172A数字多用表校准短是专门用于使用的输入连接器相同的金属34401A，以及提供从流动的空气绝缘。安捷伦34103A是一种低热量缩短为the34420A插头。它提供了一个方便，可靠的短。一个与34420A船只。
回 2楼(lilith) 的帖子
我这里发不了图 机器翻译 还不如不翻译，否则楼主应该人工翻译下。另，抵消热电势的 Offset compensation到底是怎么做的？
btw. Offset compensation应该翻译为失调补偿吧。 原文在此：
http://www.home.agilent.com/agilent/editorial.jspx?cc=IT&lc=ita&ckey=372767&nid=-536900139.0.00&id=372767
9 Tips for Making Better Resistance Measurements
简单说，这9个建议是：
1、用4线法
2、用好的测试线
3、用自动零（很多表的缺省）
4、对某些测试注意测试电压过高以免自热
5、电压限制测试使得电阻上的电压不会超过预先设定值
6、适当使用延时以便让电阻的测试有建立时间（很多表的缺省）
7、高阻测试注意不要脏了以免引起表面泄露
8、用好短路测试功能
9、Agilent有好多电阻测试配件，大家快来选用！ 还是老大翻译的到位，老大还有补充的吗？
Re
最重要的其实是第九点
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