Paper thickness measurement circuit

This example introduces a paper thickness measuring circuit, which can be widely used in automatic control circuits in papermaking, printing and other industries.
    The paper thickness measurement circuit consists of a power supply circuit, an infrared detection circuit
and a control execution circuit. After
    the AC 220V voltage is stepped down by T, rectified by VD1~VD4,
stabilized by IC2 and filtered by cJ~G, a 12V DC voltage is generated, which is supplied
to the infrared detection circuit and control execution circuit.
    The infrared detection circuit is composed of an infrared emitting diode LED1 , an infrared
receiving diode LED2, an operational amplifier integrated circuit IC1 and related
external components.
  The control execution circuit
is composed of transistors VT1, VT2 and relays Kl, K2, etc.
    After the infrared light emitted by the infrared emission tube Lrlbi passes through the paper,
it is received by the photosensitive diode LED2. When the paper is thicker,
the intensity of the transmitted light is weak, the conduction ability of LED2 is weak, and the conduction internal
resistance is large, causing the voltage of pins ④ and ⑦ of IC1 to become higher. When
the voltage of the two pins exceeds the voltage of pin ⑤ When the reference voltage is used, pin ② outputs a low level, causing the transistor VT1 to turn on, the light-emitting diode LED3 to light up, and the relay Kl to act
. Make the circuit that controls the thicker paper work. On the contrary, when the paper is thin, the voltage of pin ⑦ and pin ④ of lCl becomes low. When the voltage of the two pins is lower than
the reference voltage of pin ⑥, pin ① outputs a low level, causing the transistor VT2 to conduct, and the light-emitting diode LED 4 lights up. , relay K2 acts, making the circuit controlling
the thinner paper work.
    The voltages of pins ⑤ and ⑥ of lc1 are adjusted by potentiometers RP1 and RP2 respectively.