Common Ranging Principles of Industrial Sensors

Background Information

Industrial sensors play a crucial role in modern manufacturing, automated control, and intelligent systems, and are widely used in areas such as object detection, positioning, and thickness measurement. Different ranging technologies have their own operating principles, advantages and disadvantages, and suitable application scenarios. This article will introduce several common principles of industrial ranging sensors, including laser triangulation, laser time-of-flight, ultrasonic ranging, and phase difference ranging, to help readers better understand their strengths and weaknesses in practical applications.

Laser Triangulation Principle

1. Principle
   A laser emitted by the laser transmitter illuminates the surface of the object being measured, and the reflected light is received by the receiver. When the position of the object changes, the imaging position of the reflected light on the receiver also changes. By measuring the change in the imaging position and using trigonometric relationships, the distance between the object and the sensor is calculated. This method is typically suitable for high-precision, short-distance measurements and can measure geometric quantities such as object displacement, thickness, and vibration.
2. Advantages
   • High measurement accuracy, achieving micrometer-level or even higher precision
   • Good adaptability to the material and color of the measured object, with minimal influence from ambient light
   • Non-contact measurement, ensuring no damage or impact on the measured object
3. Disadvantages
   • Limited measurement range, generally between tens of millimeters to tens of centimeters
   • High requirements for the measurement environment, necessitating an unobstructed laser path
   • Surface roughness and reflectivity of the object can affect measurement accuracy

Laser Time-of-Flight Principle

1. Principle
   The laser sensor emits laser pulses, and after being reflected by the target, some of the scattered light returns to the sensor’s receiver. The time elapsed from the emission of the light pulse to its return is recorded and processed. Using the speed of light, the distance to the target is calculated based on this time.
2. Advantages
   • Capable of measuring long distances, ranging from several hundred centimeters to hundreds of meters
   • Fast response speed, enabling real-time measurement of rapidly moving objects
   • High measurement accuracy, with precision relatively unaffected by distance
3. Disadvantages
   • Poor measurement performance on objects with low reflectivity, requiring sufficient reflected light intensity to ensure accuracy
   • Susceptible to atmospheric conditions such as fog, rain, and smoke, which can cause laser scattering and attenuation, affecting measurement distance and accuracy
   • Relatively high equipment cost

Ultrasonic Ranging Principle

1. Principle
   An ultrasonic sensor consists of a transmitting transducer and a receiving transducer. Under electrical excitation, the transmitting transducer generates ultrasonic waves that propagate through the medium. Upon encountering an obstacle, the ultrasonic waves are reflected back and received by the receiving transducer. By measuring the time difference between the emission and reception of the ultrasonic waves and knowing the speed of sound in the medium, the distance between the sensor and the obstacle is calculated.
2. Advantages
   • Low cost and relatively inexpensive
   • Insensitive to color and transparency, suitable for measuring objects of various materials and colors
   • High accuracy in short-distance measurements and unaffected by electromagnetic interference
3. Disadvantages
   • Measurement accuracy is significantly affected by environmental factors such as temperature, humidity, and atmospheric pressure, which can alter the speed of sound
   • Limited measurement range, generally within tens of meters
   • High requirements for the reflecting surface, needing good reflective properties to ensure measurement accuracy
   • Relatively slow response speed, making it unsuitable for measuring rapidly moving objects

Phase Difference Ranging Principle

1. Principle
   There is a phase difference between the emitted light source and the received light source. By measuring this phase difference, the distance can be calculated. The transmitter emits a continuous modulated light signal, and the receiver receives the reflected light signal, comparing it with the transmitted signal. Based on the relationship between the phase difference and the distance, the measurement distance is determined. This method is commonly used for medium to long-distance detection.
2. Advantages
   • High precision, maintaining good accuracy in medium to long-distance measurements
   • Strong anti-interference capability against ambient light
   • Fast measurement speed, enabling real-time measurement of dynamic object distance changes
3. Disadvantages
   • Relatively complex system and higher cost
   • Limited measurement range, typically between tens to hundreds of meters
   • Specific requirements for the reflectivity of the measured object, as low reflectivity can impact measurement accuracy