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

Is a 4-wire resistance measurement worth the trouble? Find out!

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 internal resistance, the current through this path is nearly 0, and the impact of the lead resistance is negligible.

When measuring that same 1 ohm resistor with a 4 wire measurement, we see the new measured value. If we pull out our 2-wire measurement, we see that there’s a 6.5% difference! Clearly, a 4-wire measurement was the superior choice in this scenario.
An easy way to decide if you should use a 4-wire vs. a 2-wire measurement is to measure the resistance of your measurement lead system and compare it to the range of measurements you’re making on your device. Do the math, look at your error budget and decide if it fits within your acceptable tolerances.

The second place I see 4-wire measurements used a lot is for power supplies. Most pro-level power supplies have a capability known as “remote sense” to control the output. In a power supply, you typically set an output voltage, and the supply tries to provide that voltage regardless of the load. As the load changes, the power consumption changes. So, the supply has to sense the voltage at it’s output and adjust for dynamic loads. The problem they run into is the same – as the current changes, the loss in the supply leads changes based on Ohm’s law, and the actual power delivered to the device changes. So, you can run sense leads out to your actual device under test and the supply will adjust its output based on the voltage of the device, not the voltage at the output of the box.

#DigitalMultimeter #DMM #DMMMeasurement #DMMResistance #MeasureResistance #HowToMeasureResistance #4WireMeasurement #KelvinMeasurement #ResistanceMeasurement #DMMResistanceMeasurement #electronics #electricalengineering #computerengineering

[ElectroBOOM]

I have done 4 wire measurements before, just that I was measuring a DC motor's coil resistance of around 10mOHM, or PCB power line resistance. So I had to run like 10A or 50A through the resistance and measure the voltage across it with a DMM! I suppose a high precision 4-wire DMM would be less catastrophic??

[Factory]

This event is always exciting!
Still enjoying the fruits of my previous big WIN of the MSOX6000 6Ghz scope - It is in daily use (at full bandwidth) and I have since filled out the bench with another DSOX1204G for the higher risk DUTs.

Next up - 7.5 digit DMM and the USB based VNA! Moving up in the world.

[DrFrank-xjbc]

I'm doing 4W resistance measurements since 1989 already, when I purchased my 1st hp3458A @ university. Offset Compensation was the other feature which came with this instrument, to further reduce e.m.f. errors.
Great, that the 34465A/470A also feature both methods.

[ihsanwiguna]

since i just using my basic measuring tool, i just use 2-wire measurement so far unfortunately. you guys not only giving great products, but also useful knowledge of course

[KeysightLabs]

Welcome to day 2! How do you use 4-Wire measurements?
Sign up now for the sweepstakes and get access to the resource libraries:

[xx-mzeg]

I could die for that Keysight ruler <3

[damiankosiorek]

Well i switched to 4 wires measurments during my classess called "Semiconductor devices" led by my great proffessor Sylwester Nowocien. He teached us about small resistances and why they matter so much. That led us to the question on how accurately meassure the small resistances? Well he was like "Now look what we've gotten from our great Campus dotations" and there were those beautiful Truevolt Series 6.5 Digit Multimeters. After lectures with our precious proffessor our entire year switched immediatelly to the Truevolt series provided by the Keysight. Thank you very much Keysight! Hopefully i could get one to avoid long travles to campus to measure the stuff :D. Too expensive to buy from my student's fee :<.

[jimpyu]

These precise equipments are gold in this industry.

[yunusYT]

Every day we learn new things, just came to know about this. Thanks for great info!

[wayneparris]

A little off topic, I love the FROGGER screen saver! ON topic, thanks for clearing up this topic. What is the effect of the resistance of the sense leads in a 4 wire measurement?

[msmyrk]

Awesome description on the 4-wire stuff. I've always had troubles getting my head around 4-pin current sense resistors, and your description of DMMs is the first that's really let me get my head around it.

[RaoulB.]

Well, I've always wanted an oscilloscope since I've been interested in electronics. Right now i'm trying to repair a motherboard and attending many other projects, getting one of these instruments would be amazing for me. Let's hope for the best and congratulations to whoever wins!

[vittal]

Studying Electrical Eng... Hope to win any giveaway so I can use them for my project..

[AndreiM]

Well, I am attempting to measure ESR on Electrolytic capacitors in one faculty project. Also with constant current is easy to determine the capacitance...

[markys]

I haven't switched to 4 wire measurement yet, but after this video, I will! :D

[scruff_]

Oh I really like that E36103A power supply. Clean looks

[osgeld]

about the only time I use 4 wires is when measuring across a shunt
and grats to all the winners!

[kevincozens]

Another option available with some meters for resistance is to use the relative measurement setting. You short the leads together and set that as your zero point then take your resistance measurement.

[nicktumi]

4 wire is the best way to measure accurately. Especially for sensors! It's easy to put together different modules from Keysight via GPIB and automate everything.

[foxabilo]

I am designing a low cost lithium chemistry cell internal resistance classifier and 4 wire is essential.