What is it?

R-Cubed is a small 3.1 amp Kelvin configured current sense resistor designed for lab use. It contains a 0.1 ohm, +/-0.25% tolerance four terminal resistor. The resistor’s two terminal pairs are connected to standard 4mm banana jacks for quick setup. The current to be measured is applied to one terminal pair, and the sensed voltage is measured across the opposite pair. This methodology eliminates measurement error caused by the resistor’s terminal resistance. The terminal pairs are interchangeable, so the measured current can be applied to either pair.

Specifications:

• Current to voltage transfer ratio: 0.1 volt per 1.0 amp
• Max. Current: 3.1 amps
• Tolerance: +/-0.25%
• Resistor value: 0.1 ohms
• Banana jack type: 4mm, accepts unshrouded and retractable banana plugs
• Banana jack spacing: 3/4 inch between red and black terminals
• Internal resistor: Ohmite LVK24R100CER
• Dimensions: 1.97 x 1.97 x 0.98 inches (5 x 5 x 2.5 cm)

Usage notes

R-Cubed's upper and lower pairs of red and black terminals are interchangeable. Connect one pair of red/black terminals into the current path being measured. Connect the second pair to a voltmeter. Note that the voltmeter must be isolated or differential with high impedance for proper four terminal measurement. This is necessary to minimize current flow through the terminals being used for measurement. A digital multimeter's voltage setting is suitable. Multiply the voltage reading by ten to derive the current measurement

Why did you make it?

I needed to monitor several currents without disrupting the circuits under test, ideally with one multimeter to reduce costs and bench space. A simple way forward is installing a current sense resistor in each current path and monitoring their voltage drops. This is best done with four terminal resistors to eliminate measurement error from additional unknown resistances, such as the resistor’s leads. However, most four terminal resistors were cumbersome for lab testing, lacking insulated enclosures and banana jacks. This motivated me to create a custom PCB with an enclosure to house a four terminal sense resistor and four banana jacks.

What makes it special?

R-Cubed is quick and easy to connect in the lab. They're also compact, taking up little precious bench and lab space.