Summary of A DIY FLUXGATE MAGNETOMETER BASED CURRENT PROBE
This article introduces a sensitive, home-made current probe using a Texas Instruments fluxgate magnetometer-on-a-chip. Unlike traditional methods requiring circuit interruption and known resistors, this fully isolated sensor measures currents from single-digit microamps to 10mA without intruding into the circuit. It operates from DC to approximately 20kHz. The design leverages an integrated chip to simplify the complex analog and digital electronics typically needed for fluxgate sensors, which usually require rare mu-metal cores.
Parts used in the DIY Fluxgate Magnetometer Based Current Probe:
- Fluxgate magnetometer-on-a-chip
- Evaluation board
- Analog electronics components
- Digital electronics components
Introduction
Current measurement can be really awkward when working with circuits. Voltage measurements are (usually) straightforward, but when it comes to current measurements the story is different. One typical approach is to insert a known resistance by breaking the circuit, and then measuring the voltage across it. This is difficult if one end of the resistor is not at ground potential, because oscilloscope probes are (usually) designed with the ground leads all connected together, and it will damage things if the grounds of different channels on the oscilloscope are connected to different parts of the circuit.
This project describes a very sensitive home-made current probe that doesn’t require a known resistance to be inserted. It has not been fully characterized but the initial results are reasonably promising. It was tested at currents of the order of single-digit microamps up to 10mA (it can be assembled for higher current ranges if desired), and it functions from DC to around 20kHz, and is fully isolated.
It is based around a very exotic magnetic field sensor known as a fluxgate magnetometer. Ordinarily this is quite difficult to build due to the requirement for hard-to-find mu-metal and a mix of analog and digital electronics. However, Texas Instruments offers an entire fluxgate magnetometer-on-a-chip and an evaluation board. With some effort it is possible to build a current sensor or probe with it. It makes a handy test tool for measuring current in a circuit, in a less intrusive way than normal.
What is a Fluxgate Magnetometer?
There are several ways to make magnetic field sensors, and the fluxgate magnetometer offers very impressive sensitivity. There are slightly different topologies of fluxgate magnetometers, but in a nutshell they consist of windings around a core. If we use a Lego wheel tyre to act as a pretend core then ‘Excitation’ and ‘Sense’ windings can be placed around it as shown in the photo (the windings are the yellow and green wires in the photo).
Read more: A DIY FLUXGATE MAGNETOMETER BASED CURRENT PROBE
- How does this current probe differ from traditional measurement methods?
It does not require inserting a known resistance or breaking the circuit. - Can this probe measure DC current?
Yes, it functions from DC to around 20kHz. - What is the maximum current range tested for this project?
It was tested up to 10mA with initial results being promising. - Does this device provide electrical isolation?
Yes, the probe is fully isolated. - Why are traditional fluxgate magnetometers difficult to build?
They usually require hard-to-find mu-metal and a mix of analog and digital electronics. - What component makes building this sensor easier?
Texas Instruments offers a fluxgate magnetometer-on-a-chip and evaluation board. - Is this probe suitable for low current measurements?
Yes, it can measure currents in the order of single-digit microamps.
