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PGA460: The distance measured by the PGA460 is greater than the actual distance at 400KHz frequency

JIN YI
Prodigy 30 points
Part Number: PGA460

Tool/software:

When using the PGA460 for short-distance measurements (<350mm), there is a consistent discrepancy of about 12mm between the measured distance and the actual distance, whether using the Time-of-Flight method or directly reading the distance value from the GUI tool, which is significantly greater than the measurement accuracy of the sensor.

So, what could be the possible reasons for this issue? How can it be optimized?

Here are the test conditions and related settings:

Sensor: Closed-top 400kHz sensor

Driving frequency: 406.8KHz

Test temperature: 26°C

Other settings are as follows:

  • 0
    TI__Mastermind 43730 points

    Hello Jin,

    This looks like it may be related to your threshold setting.  Try moving the marker below a bit earlier and you could also reduce the level.  You want to be sure that you don't lower it so much that noise could trigger it, but your noise floor looks pretty good.      

     

  • 0 in reply to Eddie LaCost
    Prodigy 30 points

    Hello Eddle：

    Following your advice, I conducted tests at the same distance with three different threshold settings (high, medium, and low) as shown in the figure below. Indeed, different thresholds do affect the measurement results, with a difference of about 2mm between the three threshold settings. However, there is still a discrepancy of about 10mm from the actual target distance, which cannot be eliminated by adjusting the thresholds.

    So, please also provide further debugging suggestions.

    Additionally, I have two questions:

    1. I always thought that the PGA460 calculates the Time-of-Flight by detecting the peak of the returning echo, but this experiment found that adjusting the detection threshold affects the Time-of-Flight result even when the peak of the returning echo remains unchanged, which confuses me. How is the timing of the Time-of-Flight defined exactly?

    2. Can this discrepancy from the actual distance be compensated by software, and does this method pose any additional risks?

  • 0 in reply to JIN YI
    TI__Mastermind 43730 points

    Jin,

    I need to look into this.  I will get back to you by Monday next week.

  • 0 in reply to Eddie LaCost
    Prodigy 30 points

    I have added some test data: I took measurements at every 10mm from  within the range of 30 to 280mm, and the resulting data table is as follows:

    We can see that the offset values are around 15mm in most areas。

    The distance calculation formula is completely in line with the official recommended formula：

    The current threshold setting is as follows:

  • 0 in reply to JIN YI
    TI__Mastermind 43730 points

    Thanks for the extra data. I am looking into this and will provide a response by tomorrow.