How Gradiometer Works - proFEX MG-200 Manual

1.3 How gradiometer works

Gradiometer is a device that measures gradient of magnetic field or difference in magnetic field levels
between two points in space. Since magnetic field of any magnetized object weakens as the distance to
the object increases, it will have a gradient. Absence of magnetized object means absence of magnetic
field and therefore gradient equals 0.
Measurements of magnetic field are taken at two different points in space, where gradiometer sensors
are located – upper and lower. Difference between the measurements is called gradient and is digitally
displayed on the screen.
Magnetic field is measured in special units – "Tesla". 1/100,000 Tesla is called "nanotesla". Gradient
depends on the distance between measurement points and so the difference in measurements is tied to
the distance between them and is measured in "nanotesla over meter" – nT/m. Gradiometer MG-200
measures magnetic field in units which equal 4 nT. In order to translate the result into nT, simply
multiply the number on display by 4.
In order for gradiometer to correctly measure the gradient, its sensors must be identical in sensitivity
and precisely aligned. But sensors are susceptible to environment and first of all – changes in
temperature. As time passes changes in temperature cause mechanical and electrical changes in
sensors. These changes are miniscule but may result in increased interferences when gradiometer is
tilted during movement (sensors not balanced) or when making directional turns (sensors not aligned).
In this case sensors require tuning.
There are only two types of tuning: if interferences arise from tilting gradiometer while walking, sensor
sensitivity needs to be balanced; if interferences arise on turns (changing the direction of movement),
sensors' alignment needs to be tuned. Both types of tuning are simple, can be performed as needed and
after a little practice take only a couple minutes.
Need for tuning is decided by the user depending on the level of interference that he deems acceptable
for specific type of search.