Circuit design of the pyroelectric probe wire sens

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Abstract: This paper introduces the characteristics, design principle and circuit implementation of a photoelectric sensor for detecting the movement of silk thread in chemical fiber production

key words: photoelectric probe wire sensor; Infrared pulse

I. preface

wire detection sensor is an indispensable wire breaking detection device in chemical fiber drafting equipment. The traditional probe wire sensor mostly adopts charge induction type, which has high detection sensitivity, but it is greatly affected by ambient temperature and humidity, which affects its reliability and accuracy. The photoelectric wire probe sensor can make up for the shortcomings of the above detection methods, thus greatly improving the accuracy and reliability of wire breakage detection

II. Principle of photoelectric wire detection sensor

photoelectric wire detection sensor can detect the non-contact broken wire of the fiber spun by the textile machinery, and can cooperate with the wire cutter to cut the broken wire in time, so as to prevent the fiber from winding the machine parts

the photoelectric probe sensor uses the infrared photoelectric principle to detect the movement state of the fiber. When the fiber is normal, the fiber in the U-shaped groove of the sensor will vibrate slightly due to the drafting or winding of the machine. This jitter will continuously block the emission and reception of the infrared light on the left and right sides of the U-shaped groove, making it produce continuous infrared pulses; When the fiber is disconnected, the continuous infrared pulse decreases or disappears. The wire detector can judge whether the fiber has been disconnected by detecting and judging the frequency of the infrared pulse

III. circuit equipment and function realization

circuit composition: infrared transmitting circuit, infrared receiving circuit, amplification circuit, shaping modulation circuit, demodulation circuit, touch induction delay circuit, overcurrent protection circuit and output circuit

1. Infrared transmitting and receiving circuit (see Figure 1)

in order to keep the brightness of LED constant, LED 1, n 1, R 0, zd1 and R 1 constitute a constant current source infrared transmitting circuit, IC 2B, p h, R 2 ~ r 4 constitute an infrared receiving circuit, and the signal is output through C 1 coupling. When the infrared light energy received by P H remains unchanged, and the 7-pin output level of IC 2B remains unchanged, C 1 has no coupling signal output. When the infrared beam is repeatedly cut due to the swing of the wire, which should be noted, so that the light energy received by the pH changes, the C 1 coupling outputs a pulsating signal of the same frequency

2. Front stage amplification and shaping modulation circuit (see Figure 2)

the front stage amplification circuit is composed of R5 ~ R9 and IC 2A. R5 and R6 input bias static operating points to amplify the weak sharp pulse signal coupled from C1. The gain depends on the ratio of R8 and R9. The shaping and modulation circuit is composed of R11 ~ R13, C3 and IC 2D. The front stage sharp pulse signal is shaped and modulated into a constant amplitude square wave pulse signal

3. The demodulation circuit

is composed of D 1, R 15 ~ r 18, C 6 and IC 2c, and the positive feedback is introduced by R 18. When the current level signal frequency is lower than a certain value, the starting price in the spot market also provides opportunities for capital players with keen sense of smell. When F 1, the 8 pin of IC 2C outputs a low level; When the current stage signal frequency is higher than a certain value f 2, pin 8 of IC 2C outputs a high level. The frequency range of the critical transition zone F W = f 2 - F 1. Appropriate F W can effectively prevent the output oscillation of the critical transition zone of the detection signal, making the detection action reliable

4. Touch induction delay circuit, overcurrent protection circuit and output circuit

ic 1D, C 8, R 24 and D 4 constitute touch delay control. When the wire is broken or drawn, because the pulse signal f is less than the value of F 1, the signal input terminal in Figure 4 is low level, and the wire detector outputs a signal; When the time-delay sensing end is touched, pin 14 of IC 1D outputs a high level to quickly charge C 8, and the output is cut off. The delay time is determined by C 8 and R 24. Through this touch delay, the wire drawing operation can be carried out. The overcurrent protection circuit is composed of IC 1c and R 27. As the chairman of the Implementation Committee, R Tong Peide 27 can limit the peak current and feed back the overcurrent signal to pin 10 of IC 1a to make the output cut off quickly. D 5 plays the role of freewheeling, which can prevent the damage of electricity when the inductive load is turned on and off. It is suitable for printing the movable crown bridge model (as shown in the figure below)

IV. conclusion

after repeated design and test, all technical indicators of the infrared photoelectric probe sensor have reached a good level. Its low-level output is less than 0.1V, the normal power consumption is less than 0.3w, the load current can reach 800mA, the short-circuit protection current is 1a, the wire breaking response time is less than 0.5s, the power delay time is 4S, and the touch delay time is 15s. It can detect broken wires of different materials


[1] [Japan] Shinji Yoshino (compiled by zhangyulong, zhuxiyi and huangmeichao) Sensor circuit design manual [m] China Metrology press, 1989.12 (end)

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