Counting circuit composed of transistors

It can be used in equipment such as paper machines for detection and counting. When the magnet sweeps across L with the rotation of the drum
, an electric potential (i.e., a signal) is induced in L, VTi is
turned on, VT2 is turned off, and relay KA loses power and is released. When the working line speed of this switch
is 0.48-9.9m/s, the response distance
is 15~55mm.
    In the figure, the inductor L is wound with 6500 turns of
enameled wire with a diameter of 0.06mm on a permanent magnet . The permanent magnet
is a paper end positioning magnet (ferrite) adsorbed on the side of the paper drum.