On a separate page we give an overview of methods of measuring magnetic fields. One common way is to use search coils. When three axis measurement is needed, three search coils at right angles to each other are needed. There are broadly two ways of achieving this:
The sensor on the left has the three coils centred on each other. They are air-cored, and to get the necessary sensitivity, they have thousands of turns of wire. These examples are 10 cm square.
The sensor on the right has much smaller coils to make a smaller overall meter. To get the sensitivity despite the smaller size, the coils have iron cores. This means they cannot be centred on the same point; they are arranged separately, at right angles to each other (two are flat on the pcb at the bottom left, the third, vertical, coil is provided with a white mechanical support at the bottom right).
