Plastic bag sealing machine circuit

The plastic bag sealing machine control circuit shown is connected to a monostable delay circuit through the NE555 time base integrated circuit to control
the energization time of the electric heating element and the curing time of the heat-sealed plastic. Embed permanent magnet steel on the bakelite pressure lever of the sealing machine, and install
the reed switch KR close to the fixed table.
    Turn on the power and the power indicator light HL1
(green) lights up. L of transformer T, the output voltage
is rectified by vC, and the three-terminal voltage regulator 7812 stabilizes the voltage
and Ci, c2. Roll the wave to get 12V DC
voltage. When the bakelite pressure plate of the sealing machine
is pressed down, the permanent magnet embedded in the pressure plate is close to the
reed switch KR installed under the fixed table. The normally open contact of the reed switch
closes and the 555 time base
integrated circuit busy. power supply and enter the ready state. Press
the micro switch Sl. The IC enters the transient state, the ③ pin is at
high level, the relay KA is electrically closed, its
normally open contact is closed, the electric heating plate RL is electrically heated, and the mouth of the plastic bag is heat-sealed. At the same time, the other normally open contact of relay KA closes, causing the transistor
VT to conduct, and the heating timing indicator light HL2 (red) lights up, and at the same time, G is charged. When the delay is over, the monostable circuit composed of LC flips over
and enters the steady state again. The relay KA loses power and is released, and the electric heater RL loses power and stops heating the mouth of the plastic bag.
    After the plastic bag mouth is heat-sealed, it cannot be pulled up immediately. It needs a few seconds of curing process to prevent the weld from tearing. Setting VT and c5 is to
give the plastic being heat-sealed time to solidify after RL stops heating. When KA loses power and is released, its normally open contact is disconnected, cutting off the VT base power supply line
, and then cs is discharged. Continue to maintain the base current of VT, and the red light continues to light up. After a few seconds, the island discharge is completed. When the red light goes out, relax and pull up
the bakelite pressure plate, the permanent magnet will also leave, the normally open contact of the reed switch KR will be reset, and 1C will lose power and stop working.