SLOA341 October   2024 LOG300

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Description
    1. 2.1 Basics of Ultrasound Sensing
    2. 2.2 Advantages and Disadvantages of Ultrasonic Sensing
    3. 2.3 Ultrasonic Transducer
      1. 2.3.1 Transducer Construction
      2. 2.3.2 Transducer Frequencies
    4. 2.4 Transducer Topologies
    5. 2.5 Blind Zone Effect on Minimum Distance
    6. 2.6 Transducer Drive
    7. 2.7 Ultrasonic Echo and Signal Processing
      1. 2.7.1 Digital Gain or Fixed Gain
      2. 2.7.2 Time-Varying-Gain
      3. 2.7.3 Automatic Gain Control or Logarithmic Amplifier
      4. 2.7.4 Logarithmic Amplifier vs Logarithmic Detector
  6. 3LOG Detector Amplifier and the Advantages Over Conventional Opamps
  7. 4Application
    1. 4.1 Double Paper Feed and Paper Thickness Detector
      1. 4.1.1 Schematic Implementation
      2. 4.1.2 Material Thickness Detector
    2. 4.2 Bubble Detector
    3. 4.3 Material Detection
    4. 4.4 Distance or Proximity Detection
  8. 5Summary
  9. 6References

4.1.2 Material Thickness Detector

Material thickness detection also works in a principle very similar to double paper feed detection and the same setup can be used for this application as well. This article demonstrate the thickness detection of papers with different GSM (gram per square meter) count. Higher the GSM, higher can be the weight and thickness of a paper.

Similar to the double feed detection, in this application also, the material (here paper) is placed between the two ultrasonic transducer (Tx and Rx). As the transmitted signal passes through the paper, the signal gets attenuated and the strength of received at the Rx depends on the thickness of the paper. Thicker the paper, more signal can get absorbed resulting in higher attenuation. This can be detected as a drop in the received signal strength.

Table 4-1 shows the output signal of the LOG300 at the receive signal chain with respect to paper of different thickness and number of such paper placed in between the two transducer

Table 4-1 LOG300 Output (V) vs Paper Thickness
No of Sheet 70GSM Paper 100GSM Paper 200GSM Paper 270GSM Paper
No paper 4.8V 4.8V 4.8V 4.8V
Single 3.1V 2.92V 2.76V 2.6V
Double 0.38V 0.36V 0.33V 0.31V

As shown, the paper thickness increases the signal attenuation also increases resulting in lower voltage at the LOG300 output