Printing machine photoelectric paper break detection circuit

The photoelectric paper break detection method has
the characteristics of high detection sensitivity. It is based on
the control circuit principle of the JJ201 web double-sided two-color offset printing machine. The GK-4A photoelectric detection control circuit
is shown in the figure.
    1) During normal printing, the paper tape passes between the sending and receiving heads
, and the photoelectric end is irradiated by weak light, and the resistance of Vp is very large. It
forms a voltage dividing circuit with R1, Bian, and RP, so that
the U&<O of transistor VT1 . 7V, vri is cut off, VT2 is also cut off, relays
KI and K2 are both in the release state, and the control circuit has no signal
output.
    2) When the paper tape is broken, the photoelectric tube illuminates strongly, the photocurrent
increases, and the resistance decreases, causing the base potential of VT1 to rise and VT1
to conduct. As Uh2 rises, VT2 is also turned on, relay K1 is closed, and its normally open contact is closed, causing relay K2 to also be closed. At this time, the
control circuit has a signal output to stop the machine.