Weston Braun's Open Source Design Rogowski Coil Shows How to Build the Coil and Integrator Circuit
Measure up to 25 MHz and 30 amps.
A Rogowski coil is a popular choice for measuring AC currents in a conductor. Their split design makes it trivial to wrap them around a lead or wire. While commercial probes exist, that did not stop Weston Braun from designing a well-documented, open source Rogowski coil and amplifier that almost anyone can build.
Braun's Rogowski coil current probe has two pieces. The sensing coil has a free end held by a captive o-ring. It's small enough to fit between a TO-220's leads. The other part is an amplifier to condition the signal. It converts the current induced in the sense coil to a voltage.
The sense coil is a DIY design. You need some PTFE tubing, 36 AWG magnet wire, a coax, a 3D-printed enclosure, and a few hardware pieces to build one. Braun provides a list of sources for the parts and instructions on building the coil.
Braun used an off-the-shelf project box with a custom-designed PCB for the amplifier circuit. The circuit is an op-amp-based, non-inverting integrator with an analog high-pass filter.
Overall the probe has a usable bandwidth range from 800 Hz to 25 megahertz with a sensitivity of 0.1 volts per amp. The maximum measurable current is 30 amps. The integrator's SMA output terminates into an oscilloscope with a one megaohm input.
The first version of the PCB did have some interference issues with LTE and Wi-Fi signals. A second revision should resolve those issues, but it still needs testing.
Braun open sourced the entire probe and provided excellent design notes. For example, the Rogowski Relief GitHub repo contains KiCad schematics, PCB files, gerbers, and STLs for the enclosure. Additionally, there are even canned LTSpice files available for simulating design changes!
