Design of infrared photoelectric wire-detecting sensor

1. Introduction

The wire sensor is an indispensable broken wire detection device in chemical fiber drafting equipment. Most traditional wire sensors adopt charge induction type, which has high detection sensitivity, but is greatly affected by ambient temperature and humidity, thus affecting its reliability and accuracy. Photoelectric wire sensors can make up for the shortcomings of the above detection methods, thereby greatly improving the accuracy and reliability of broken wire detection.

2. Principle of photoelectric wire sensors

Photoelectric wire sensors can perform non-contact broken wire detection on fibers spun by textile machinery, and can cooperate with the wire cutter to cut off the broken wire in time to prevent the fiber from winding around the machine parts. The

photoelectric wire sensor uses the infrared photoelectric principle to detect the movement state of the fiber. When the fiber is normal, due to the machine's drafting or winding and other actions, the fiber located in the U-shaped groove of the sensor will have a slight shake. This shake will continuously block the emission and reception of infrared light on the left and right sides of the U-shaped groove, causing it to produce continuous infrared pulses; when the fiber is broken, the continuous infrared pulse decreases or disappears, and the wire detector can determine whether the fiber is broken by detecting and judging the frequency of the infrared pulse.



3. Circuit equipment and function realization

Circuit composition: infrared transmitting circuit, infrared receiving circuit, amplifying circuit, shaping modulation circuit, demodulation circuit, touch sensing delay circuit, overcurrent protection circuit and output circuit.

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

In order to keep the brightness of the light-emitting diode constant, LED 1, N 1, R 0, Z D1 and R 1 constitute a constant current source infrared transmitting circuit, IC 2B, PH, R 2 ~ R 4 constitute an infrared receiving circuit, and the signal is coupled and output through C 1. When the infrared light energy received by PH remains unchanged, the output level of pin 7 of IC 2B remains unchanged, and C 1 has no coupled signal output. When the light energy received by PH changes due to the repeated cutting of the infrared beam by the swing of the silk thread, C 1 couples and outputs a pulsating signal of the same frequency.

2. Pre-amplification and shaping modulation circuit (see Figure 2)

The pre-amplification circuit is composed of R 5 ~ R 9 and IC 2A. The static working point is biased by R 5 and R 6 to amplify the weak sharp pulse signal coupled from C 1. The gain depends on the ratio of R 8 and R 9. The shaping modulation circuit is composed of R 11 ~ R 13, C 3 and IC 2D, which shapes and modulates the pre-stage sharp pulse signal into a square wave pulse signal with equal amplitude. 3. Demodulation circuit It is composed of

D

1, R 15 ~ R 18, C 6 and IC 2C, and positive feedback is introduced by R 18. When the frequency of the pre-stage signal is lower than a certain value F 1, the 8th pin of IC 2C outputs a low level; when the frequency of the pre-stage signal is higher than a certain value F 2, the 8th pin of IC 2C outputs a high level. The frequency range of the critical transition zone is FW = F2 - F1. Appropriate FW can effectively prevent the output oscillation of the critical transition zone of the detection signal, making the detection action reliable.

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

IC 1D, C8, R24 and D4 constitute touch delay control. When the wire is broken or wire drawing state, since the pulse signal F is less than the F1 value, the signal input end of Figure 4 is low level, and the wire detector outputs a signal; when the delay sensing end is touched, the 14th pin of IC 1D outputs a high level, quickly charges C8, and the output is cut off. The delay time is determined by C8 and R24. Through this touch delay, the wire drawing operation can be performed. The overcurrent protection circuit is composed of IC 1C and R27. R27 can limit the peak current and feed back the overcurrent signal to the 10th pin of IC 1A to quickly cut off the output. D 5 plays a role of freewheeling, which can prevent the circuit from being damaged when the inductive load is switched on and off.

IV. Conclusion

After repeated design and testing, the infrared photoelectric wire detection sensor has achieved good technical indicators. Its low-level output is less than 0.1V, normal power consumption is less than 0.3W, load current can reach 800mA, short-circuit protection current is 1A, broken wire response time is less than 0.5s, power delay time is 4s, touch delay time is 15s, and it can detect broken wires of different materials.