Elektor magnetometer

[Ian Macmillan]

In the May 2007 issue (No.365) an article describes a magnetometer using an
unmodified mains transformer as the sensor.

I would have thought that the closed magnetic circuit would tend to cancel
out changes in the induced voltage due to a varying external field. Probably
not perfectly, but still...

I'd be interested in the opinion of the experts.

All the best
Ian Macmillan

 

[Fred Bartoli]

Ian Macmillan a écrit :

In the May 2007 issue (No.365) an article describes a magnetometer using an
unmodified mains transformer as the sensor.

I would have thought that the closed magnetic circuit would tend to cancel
out changes in the induced voltage due to a varying external field. Probably
not perfectly, but still...

I'd be interested in the opinion of the experts.

Don't have the article, but the general way of doing this is by
alternatively saturating or not the core.
In the unsaturated state, the core will divert the external flux line
from the coil, while in the saturated state these external flux line can
reach the measuring coil.

Anyway I can see how to use a mains transformer for this, but certainly
not unmodified.
Can you post a scan?

 

[Ian Macmillan]

"Fred Bartoli"

Ian Macmillan a écrit :

Don't have the article, but the general way of doing this is by
alternatively saturating or not the core.
In the unsaturated state, the core will divert the external flux line
from the coil, while in the saturated state these external flux line can
reach the measuring coil.

Anyway I can see how to use a mains transformer for this, but certainly
not unmodified.
Can you post a scan?

The circuit simply connects the windings of the transformer in series to the
differential inputs of a LM380 without any bias current in the coil.

Years ago I made a DC ammeter using the principle you mention in a ferrite
core to vary the MS ratio of a multivibrator.

All the best
Ian Macmillan