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  • What is the difference between induction, capacitance and ultrasonic sensors?
  • Editor:Jiande Antai Power Capacitor Co.,LtdDate:2021-12-13 10:16 Click:
Sensing technology is widely used in a variety of industries, including the oil and gas, pharmaceutical, and food and beverage industries. In order to select the most suitable sensor, factors to consider should include the environment, size, installation type, housing and connection options, in this paper, a brief overview of induction sensor, capacitance sensor and ultrasonic sensor principle, characteristics, uses and precautions.
1, induction sensor
The solid state element uses the principle of inductive magnetic field to sense the presence or absence of metal objects. Detection of ferromagnetic metal materials, suitable for use in dirty wet areas, dust proof but sensing distance is limited (maximum 50mm)
Working principle of induction sensor
Induction sensor structure has four basic components, namely coil, oscillator, trigger circuit and output end.
The sensor uses an oscillator to form a high frequency field; The coil radiates the field at the sensor tip, forming a sensor field. When a metal object enters the sensing field, eddy current is introduced into it, reducing the energy emitted by the oscillator. When the energy drops low enough, the oscillator will stop. The trigger circuit will change the state of the output switch when it senses the oscillation stop.
Metal objects oscillate less as they get closer to the sensor tip and more as they move away, which is essentially how inductive sensors work.
① Suitable for use in dirty environment, not affected by moisture or dust; ② No moving parts, that is, no mechanical wear; (3) Compared with other sensing technologies, the surface dependence is lower; (4) No blind area; ⑤ Detection does not depend on color
Induction sensor application
① Assembly line ② Machine tool ③ Metal detection of material/object ④ Part classification ⑤ Identification of ferrous and non-ferrous metals (ferrous selective sensor only)
2, capacitance sensor
Capacitive sensor structure has four basic components, namely sensor board, oscillator, trigger circuit and output terminal.
The target object and the sensor board constitute the oscillator feedback circuit. When the object is close to the sensor plate, the feedback capacitor appears; When large capacitors appear, they start oscillating. The trigger circuit senses the level of oscillation and can be controlled to change the state of the switching device at the output.
The oscillation amplitude decreases as the object moves away from the sensor tip and increases as it approaches. In essence, it is the working principle of capacitance sensor.
(1) Detection of metal, non-metal, solid and liquid; (2) can penetrate some materials (product packaging); Solid state, no wear, long service life; ④ There are many configurations.
Precautions for capacitance sensors
The sensing distance is short, with the change of the target material (≥ 25mm); Susceptible to environmental impact, humidity can affect the sensor output; ③ Do not choose its target at all, it is important to control the object close to the sensor (false trigger).
Capacitive sensor applications
(1) liquid level sensing (2) product filling line (3) Plastic parts detection (4) Material handling pallet detection (5) irregular objects
3, ultrasonic sensor
Ultrasonic sensors detect objects using a constant speed of sound.
Based on the principle that sound travels at a relatively constant speed, the time spent by ultrasonic wave to leave the sensor and reflect back to the target object is proportional to the distance of the target object.
Sensors emit sound pulses that reflect objects entering the wave field. The reflected sound is received by the sensor; The echo of the sound wave produces an output signal when the object is within a specified range. In essence, it is the working principle of ultrasonic sensor.
Advantages of ultrasonic sensors
① Does not depend on the color of the object or the light reflectance; ② Can ignore the background object; (3) Detection of solid and liquid; (4) with the linear response of the distance, that is, when connected with the measuring device, the distance indication can be given; ⑤ Large sensing range up to 15m
Notes for ultrasonic sensors
① Noisy noise can give false readings; ② It may be difficult to sense sound-absorbing objects in a longer range; ③ Make sure the square planes are aligned.
Application of ultrasonic sensor
① Distance and height measurement ② industrial level control ③ Glass and transparent object detection
④ Detect missing parts or objects
The biggest disadvantage of ultrasonic is that water mist and particles can also trigger signals, and the applicable scenarios are more limited!

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