The vibrograph pickup consists of transformers 1 and 2 w ith
air gaps a and b. The transformers are rig id ly mounted on lead
ring 3 which is suspended from the housing by means of springs
4 and 5 so th a t the two air gaps are equal. Prim ary windings 6
and 7 of the transformers are connected in series; secondary
windings 8 and 9 are connected so as to oppose each other, w ith
the undisturbed position corresponding to zero resultant v o ltage.
V ib ra tio n of the housing varies the air gaps and, consequently,
the magnetic flux varies together w ith the o u tp u t v o ltage.
W hen the air gap of one transformer is reduced and its
output voltage increases, the air gap of the other transformer
increases an d the voltage induced in its secondary w in d in g is
reduced. Thus, induced in the secondary w indings is a series of
m odulated waves of voltage of average frequency, whose envelope
represents the am p litu d e of v ib ratio n.
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