Paper tension control circuit

 The given, proportional amplification, proportional integral and power amplification circuits are shown in the figure. In the figure, RPt is the given potentiometer. The integrated operational amplifiers
Nl and N2 (F004C) are the proportional amplification stage and the proportional integral stage respectively, and the transistors VTl (3DG12B) and VT2 (3DD15C) form
the power amplification stage. During tension pre-selection, set switch S2 to the "manual" position, and adjust RP1 to input 0-12V DC voltage into the base of transistor
VT1 through resistor Rs. As the given voltage increases, VT1 becomes saturated and deepens. After VT1 is turned on, the base potential of VT2 rises, so VTZ is also turned on, and the 24V
DC voltage is applied to both ends of the magnetic powder brake CZ1 (or C22) coil through switch S3. By controlling the size of the given voltage, the VT2 collector current
Id changes, that is, the brake current is controlled, so that different braking torques can be obtained. When VTZ changes from on to off, the coil CZ1 or
C22 will generate a back electromotive force impact vrz. Therefore, a diode VD2 with a freewheeling function is connected in parallel to czl and C22 to provide a path for the back electromotive force,
thus protecting VT2. .
    During normal printing. Switch S2 is set to the "automatic" position, and the given signal taken out by RP1 is sent to the inverting input terminal of Nl through the resistor Rt. After
N1 proportional amplification, its output is sent to the N2 inverting input terminal through the wind. After N2's proportional amplification and proportional integration, the output positive voltage signal is sent to the
power amplifier stage through S2 and Shu.