DIY acoustic AC magnetic field Gaussmeter

Introduction

This device is a Gauss sensor, which makes magnetic fields audible through a headphone:

Acoustic Gaussmeter

This is why I needed the Gausmeter: A hole had to be made in the concrete floor of my bathroom. The problem was that the water and drain pipes hidden in the floor, can't be located with an ordinary metal detector because of the rebar. Therefore, I developed a Gauss sensor that is capable to do so. But the Gauss sensor has more applications:

• Detection of low-frequency magnetic fields in general
• Locate electrical wiring, copper water pipes and plastic drain pipes in walls and even concrete floors
• Locate buried cables
• Finding faults in electronic equipment from the outside

The circuit

The magnetic field is picked up by a radial type inductor, which signal is amplified and fed to the headphone. The sensitivity can be adjusted with a potentiometer. In the most sensitive position, the magnetic field of a transformer can be detected over 1 meter distance.

Acoustic Gaussmeter circuit
Acoustic Gaussmeter PCBAcoustic Gaussmeter PCB with SMD 0603 components

Gauss sensor applications

Selective detection of copper water pipes in concrete floors

To locate a copper water pipe hidden in a concrete floor, I have applied an AC current through the water pipe. The current is tapped from a spot welder: http://www.avdweb.nl/tech-tips/spot-welder.html. In lack of such a device, you can use a transformer that can deliver enough current. I used a current of 40A, but I suppose that a lower current will work in many cases too.

Locate plastic drain pipes in concrete floors

Of course, an ordinary metal detector can't detect plastic drain pipes hidden in concrete floors. To generate a magnetic field inside the pipe, I used a coil of 1mH that was connected to a square wave 3V / 1 kHz from a function generator. The coil can be transported into the pipe easily by flowing water, if a strip of plastic is attached to the coil and very thin wire is used.

Locating plastic drain pipes in concrete floors

Locate electrical wiring in walls

The wire has to be loaded with for instance a lamp; else there is no magnetic field.

Locate buried cables

The Gauss sensor can locate buried cables at a depth of several meters if the line is sufficiently loaded.

Finding faults in electronic equipment from the outside

Since each electronic circuit has its own characteristic sound, you can inspect a defect apparatus with the Gaussmeter without opening it. For example, you can inspect a broken laptop: is there something wrong with the switching power supply, processor or high voltage board.