2-Wire vs. 4-Wire Resistance Measurement (Kelvin) + Wave Winners!

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Today's tip is all about how 4-wire resistance measurements work, as well as how a power supply remote sense capability uses the same principles.

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4 wire Kelvin resistance measurement overview: When can you use a two wire measurement, and when should you switch to a 4-wire measurement? If you don’t know you’re in luck, because that’s what we’re covering today! measurement. Measuring resistance is often straightforward – you just grab your leads and go crazy.

There are times when a standard 2-wire measurement just won’t do the job, so you have to switch over to a 4-wire measurement. The two main cases I’ve seen people do this, and we’ll get hands-on with each of these in a moment.

The first is using a DMM to measure small resistances. The second is supplying dynamic currents with a power supply. Let’s start with the resistance measurement of a DMM. A DMM makes resistance measurements by supplying a known current out to the device, and then measuring the DC voltage drop across the outputs. We can actually see this if we measure the device’s output during a resistance measurement.

So, let’s actually make a measurement. Here’s a quick measurement of a 1 ohm resistor – let’s store that value away for later. You might think this looks good, but there’s a problem. The DMM’s test leads are in series with the device. The resistance of the leads causes a small voltage drop, tricking the DMM into thinking there’s a higher resistance. For larger resistance measurements this isn’t a problem, but when you’re measuring small resistances this effect can be significant. Fixture resistance is also a problem in automated testing environments where you have long cables, multiple chained connections, and a multiplexer or relays between the device and the DMM. So, what we can do instead is move the voltage measurement from inside the DMM to the point of test with a second pair of leads. Now we have four leads, hence a 4-wire measurement. These two leads source current, and these two leads make the actual measurement. Because the voltage measurement has a large interna ... https://www.youtube.com/watch?v=yCyz1Jv8iU8