There is some merit to summing-in a fixed DC voltage to bring the standing signal closer to zero, for example during testing with a 'scope or DVM connected. But it's not strictly needed for real-world operation, so don't try too hard to make it zero, you will never achieve it, and you will see that the residual coil null drifts around, due to thermally-induced mechanical effects. Take the coil out in the direct sunshine, watch the null move significantly! Indoors, the coil will pick up larger items 'nearby' ie. within a metre or two. Moving the coil from 1 metre away from a metal shelf to 1.1 metre away will be detectable. When placed close to real ground, you will get a measureable signal, but it will still be much less than the residual coil null value.
Also, the full-wave rectifier should have its' output buffered, so the subsequent stage doesn't 'ruin' its precision.
Also, the full-wave rectifier should have its' output buffered, so the subsequent stage doesn't 'ruin' its precision.
Comment