Chapter 8 Tutorial

Measurement Fundamentals

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For 4-wire ohms, separate “sense” connections are required. Since no current flows in the sense leads, the resistance in these leads does not give a measurement error.

RI tThe 4-wire ohms method provides the most accurate way to measure small resistances. Test lead, multiplexer, and contact resistances are automatically reduced using this method. The 4-wire ohms method is often used in automated test applications where long cable lengths, input connections, and a multiplexer exist between the internal MWW and the device-under-test.

The recommended connections for 4-wire ohms measurements are shown in the diagram on the following page. A constant current source, forcing current b through unknown resistance k, develops a voltage measured by a dc voltage front end. The unknown resistance is then calculated using Ohm’s Law4

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HP 34970A manual To Amplifier Analog-to-Digital Converter