Two-Point and Four-Point Methods for Measuring Small Resistances *
|Areas of Science||
Electricity & Electronics
|Time Required||Short (2-5 days)|
|Prerequisites||To do this project, you should be familiar with Ohm's Law, and with the basics of using a digital multimeter (see our Multimeter Tutorial to learn more).|
|Material Availability||This project requires two multimeters.|
|Cost||Average ($50 - $100)|
Measuring the value of a resistor with a multimeter is pretty simple. You set the multimeter to measure resistance, connect the two leads to the resistor (possibly using some handy alligator clips), and read the resistance value. This is called a two-point measurement (one probe on each of the two resistor leads). But what if the resistance you want to measure is very small, in the milli or micro-ohm (mΩ or μΩ) range? This can introduce problems because many low-cost multimeters are not designed to measure resistances this small directly. The contact resistance between the test probes and the object, or even the resistance of the leads themselves, can also throw off the reading. One way around this problem is to make a four-point resistance measurement, also referred to as a "Kelvin measurement." See the All About Circuits reference in the Bibliography for a detailed explanation of this measurement technique.
Can you use the four-point method to measure the resistance of some objects with small resistances? Small metal objects you can find around your house, like those in Figure 1 (coins, nails, and screws etcetera) should work well. How do results from the four-point method compare to those from the usual two point-method? Is one method more accurate? What about comparing the two techniques to measure resistors? Is the four-point method necessary for larger resistances?
Figure 1. The normal two-point method for measuring resistance. The multimeter cannot accurately measure the very low resistances of these objects.
Note: typically four-point resistance measurements are made using Kelvin clips, which are very expensive. For purposes of this experiment, you should be able to use regular alligator clip test leads to connect to your multimeter probes. You can also purchase banana to alligator adapters, but make sure that the banana plugs are the right size for your multimeter.
Original project by Charlie Zhai, AMD.
Edited by Andrew Olson, Ph.D., and Ben Finio, Ph.D., Science Buddies
- Kuphaldt, T.R., 2003. "Kelvin (4-wire) Resistance Measurement," All About Circuits: Volume I—DC [accessed April 12, 2006] http://www.allaboutcircuits.com/vol_1/chpt_8/9.html.
Cite This PageGeneral citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.
Last edit date: 2017-07-28
- Kuphaldt, T.R. (n.d.). Kelvin (4-wire) Resistance Measurement. All About Circuits: Volume I—DC. Retrieved July 9, 2016 from http://www.allaboutcircuits.com/vol_1/chpt_8/9.html.
- Nuckolls, B. (n.d.). Practical Low Resistance Measurements. The AeroElectric Connection. Retrieved July 9, 2016 from http://www.aeroelectric.com/articles/LowOhmsAdapter_3.pdf.
- If you need to brush up on the basics of current, voltage, and resistance, the following references should be helpful:
- Science Buddies. (n.d.). How to Use a Multimeter. Retrieved July 9, 2016 from http://www.sciencebuddies.org/science-fair-projects/how-to-use-a-multimeter.shtml
- Mastascusa, E.J. (n.d.). An Introduction to Electrical Measurements. Department of Electrical Engineering, Bucknell University. Retrieved July 9, 2016 from http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Measurements/MeasIntro.htm.
- An online source for information on Kirchhoff's Laws is:
Burley, I. et al. (n.d.). Kirchhoff's Laws. Introductory Physics Notes, University of Winnipeg. Retrieved July 9, 2016 from http://theory.uwinnipeg.ca/physics/curr/node8.html.
News Feed on This Topic
- Investigate the temperature dependence of resistance by repeating the measurements at different temperatures. You can use a hair dryer to heat up the resistors and conductors (or put them in the refrigerator or freezer for awhile). Keep in mind that the metals are normally very good thermally conductive material, so their temperatures can change rapidly.
- For a slightly more advanced project, see the article by Bob Nuckolls in the Bibliography (Nuckolls, 2004) on building a simple circuit for making accurate 4-wire resistance measurements with a single multimeter.
Ask an ExpertThe Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.
Ask an Expert
If you like this project, you might enjoy exploring these related careers:
ElectricianElectricians are the people who bring electricity to our homes, schools, businesses, public spaces, and streets—lighting up our world, keeping the indoor temperature comfortable, and powering TVs, computers, and all sorts of machines that make life better. Electricians install and maintain the wiring and equipment that carries electricity, and they also fix electrical machines. Read more
Precision Instrument & Equipment RepairerOne of the basic truths in the universe is that objects tend to go from a state of higher organization to a state of lower organization over time. In other words, things break down, and when those things are precision instruments or equipment, they require the services of very specialized technicians to restore them to their working order. Precision instrument or equipment technicians often combine a love of music, medicine, electronics, or antiques with delicate mechanical repair work. Read more
Electrical Engineering TechnicianElectrical engineering technicians help design, test, and manufacture electrical and electronic equipment. These people are part of the team of engineers and research scientists that keep our high-tech world going and moving forward. Read more
News Feed on This Topic
Looking for more science fun?
Try one of our science activities for quick, anytime science explorations. The perfect thing to liven up a rainy day, school vacation, or moment of boredom.Find an Activity
Explore Our Science Videos
Paper Rockets - STEM Activity
How to make an anemometer (wind speed meter)
Slow Motion Craters - STEM Activity