FLUKE 2557732_6200_ENG_A_W 电路图.pdf

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1、Application Note From the Fluke Digital Librar y y 2x4 wire resistance simplifi es precision measurements Using two wires to measure resistance is convenient, but causes measurement error. You can virtually eliminate this error by using four leads and a multimeter with separate source and measure te

2、rminals. Unfortunately, adding addional leads and connections makes the measurement more complicated. You have additional leads to connect and you may have to swap clips and probes as you change from voltage to resistance. Now a new concept with new technology enables you to take four-wire resis- ta

3、nce measurements with just two leads. Why measure resistance with four wires? Managing two leads can be chal- lenging enough, especially when you are measuring tiny compo- nents in tight spaces. But trying to check a small solder joint, fl ex connector or chip resistor with four leads can be a real

4、trial. Switching lead confi gurations can lead to swapped banana plugs and measurement mistakes. And changing from voltage probes to Kelvin leads and back takes time. So why measure resistance with four wires? Using two wires to measure voltage does not seriously impact measurement accuracy. The vol

5、tage input on a multimeter generally has a 10 Megohm input impedance, so very little current fl ows in the leads, and the result- ing voltage drop in the leads is negligible. Current measure- ments are also not signifi cantly affected by series lead resistance. However, resistance measure- ments are

6、 subject to inaccuracies because of lead resistance. When performing a resistance measurement the multimeter switches a current source into the measurement loop. The current is driven through the unknown resistance and the multimeter measures the resulting voltage drop. If there are only two leads,

7、as shown in Figure 1, the source current travels on the same path used to measure the voltage drop. The measurement leads are not perfect conductors and have some series resistance of their own. By driving the current through the measurement leads, we see not only the voltage drop across the unknown

8、, but also voltage drop for each lead. Thus, we end up measuring the combined resis- tance of the positive lead, the unknown, and the negative lead. If we use four leads, the source current and the measurement can be separated. The meter terminals are called “Source” for the current supply and “Sens

9、e” for the volt- age input. Rlead Isource Runknown Rlead Figure 1: Two-wire resistance measurements introduce error due to voltage drop in the test leads. Rlead sense lo source lo source hi sense hi Isource Runknown Rlead Figure 2: Four-wire resistance measurements eliminate current in the voltage l

10、eads and eliminate this source of error. RadioFans.CN 收音机爱 好者资料库 2 Fluke Corporation 2x4 wire resistance simplifi es precision measurements The series resistance in the Source leads does not affect the current fl ow. And the measure/ sense leads have almost no current fl ow because of the meters hig

11、h input impedance. This means there is no I x R volt- age drop in the measure leads. So, we measure only the voltage drop across the unknown resistor due to the source current fl owing through it. Introducing 2x4 wire ohms A patented new technology from Fluke maintains the convenience of using two l

12、eads, but delivers the measurement performance of a 4 wire method. The new Fluke 8845A and 8846A Precision Multimeters have a special set of input connectors. They are completely compatible with standard 4 mm banana plugs. But on the inside, each jack is split into two contacts: one source and one m

13、easure. Specially-designed test leads have two conductors per lead, again, one source and one measure. The leads align with the contacts inside the jacks and carry the separate source and measure signals over the full length of the leads. Fluke Corporation PO Box 9090, Everett, WA USA 98206 Fluke Eu

14、rope B.V. PO Box 1186, 5602 BD Eindhoven, The Netherlands For more information call: In the U.S.A. (800) 443-5853 or Fax (425) 446-5116 In Europe/M-East/Africa (31 40) 2 675 200 or Fax (31 40) 2 675 222 In Canada (800) 36-FLUKE or Fax (905) 890-6866 From other countries +1 (425) 446-5500 or Fax +1 (

15、425) 446-5116 Web access: http:/www.fl 2006 Fluke Corporation. All rights reserved. Printed in U.S.A. 1/2006 2557732 A-EN-N Rev A Pub_ID: 11045-eng Rev 01 Fluke. Keeping your world up and running. At the far end of the leads, clips and probes that maintain separation between source and measure signa

16、ls can deliver 4-wire performance right to the component under test. A new line of clips and probes is available, all of which bring four wires right up to the point of connection. They include: Test probes Alligator (Kelvin) clips Tweezers RleadRlead Imeasure Runknown Figure 3: 2x4 wire ohms techno

17、logy uses special split banana jacks and leads to deliver 4-wire performance with 2 leads. All of these accessories may be used for measuring 4-wire resis- tance or voltage, so you wont be tempted to use bulky Kelvin clips to measure voltage. 2x4-wire ohms makes it easier to make accurate resistance measurements, without having to change cable confi gurations and without having to work with a bench full of silicone spaghetti. RadioFans.CN 收音机爱 好者资料库