Introduction: 4-wire Kelvin Precision Resistor Box
A little side project that can be finished in less than 10 minutes, but still applies as a useful tool for an electronics lab. As I was working on the development of a bigger project, I realised I would need some sort of calibration tool.
So, there you have it, a 4-wire Kelvin measurement Resistor box. It is intended to allocate any 2512 footprint resistor and 4 banana plugs.
The original idea was to use it with 2412 Vishay Precision resistors, which offer 0.01% precision and 2 PPM temperature coefficient, as a cheap way of calibrating an instrument. But this thing also turn out to be useful as a means of testing shunts and check their actual value with a multimeter.
Step 1: Features
The design is anything but complex:
- 2512 SMD footprint
- 4-wire Kelvin connection
- 4 mm holes for banana jacks
- 3.2 mm holes for mounting it inside a little case.
Step 2: Theory of Operation
A 4-wire Kelvin measurement setup, is a way of measure the value of a resistor subject, neglecting the wires parasitics involved in the process.
As shown the picture, the method consists in circulating a known current through the resistor under test via two terminals (or two "wires") and then measure the voltage drop across it.
This way, we could know the value of very low resistance shunts with very precise results, which is not achievable for the regular multimeter. For this task, we require a good multimeter in the milivolt range and a reliable source of current.
If you want to know more about this topic, click on the link bellow:
Step 3: Materials
The parts list is pretty short as well:
- PCB Board. You could order it from your favorite supplier.
- A 2512 resistor.
- A set of 4, 4 mm banana jacks.
- A set of 4, 3x10 mm self-tapping screws.
- 3D printed case.
Step 4: Experimental Results
As you can see, the operation is pretty simple. In the photos, I'm performing some tests to a 0.02 ohm resistor, circulating 2 and 4 amps through it. I have two wires carrying current connected to a pair of red and black terminals, and measuring the voltage drop in the other pair.
This way, I could check for the real value of the resistor. In this case:
- 39.82 mV / 2 A = 0.01991 ohms. 0.5% of variation from 0.02 ohms
- 81.68 mV / 4 A = 0.02042 ohms. 2.1% of variation from 0.02 ohms
This seemed like a really bad temperature coefficient for this resistor.
Step 5: Documentation
The archive below contains all the information to replicate this project.
CAD files (Fusion 360 and EAGLE 9.X):
- F360 assembly project (Assembly.f3z)
- F360 electronics project (F360_Resistor_Box.f3z)
- F360 Schematic (F360_Resistor_Box_sch.fsch)
- F360 PCB layout (F360_Resistor_Box_PCB.fbrd)
- EAGLE Schematic (EAGLE_Resistor_Box_sch.sch)
- EAGLE PCB layout (EAGLE_Resistor_Box_PCB.brd)
- STL models of the featured box (Box.stl)
Printable files:
- Schematic (Resistor_Box_Schematic.pdf)
Production files:
- Gerber files (Resistor_Box_Gerber.zip)
This project was made entirely with Fusion 360. Electrical files of the project have been exported as Fusion 360 and EAGLE 9.X compatible files. Google Drive link to access the project files:
https://drive.google.com/file/d/1V4Ewm8NjrSIrAq6tA...
I hope you liked this project! I encourage you to comment and share this article, so I could write better ones in the future. I would be glad to answer all of your questions.
Enjoy!
You can also follow me on Instagram!
