The data sheet (https://www.robotshop.com/media/files/pdf2/pli-06-instruction.pdf) for the LIDAR Lite v3 mentions under Performance that the repetition rate is ~50 Hz default and 500 Hz max, and the update rate is 270 Hz typical, 650 Hz fast mode and >1000 Hz short range only. I always thought repetition rate and update rate are the same and are interchangeable terms. Can anyone please explain what the difference between them is?
I’m also not sure what the default pulse rate (i.e. how many pulses transmitted per second) is for this LIDAR. Is it 256 pulses per second?
Thanks!
@belaldaouk: Here are some clarifications concerning the LIDAR Lite v3 (LLV3) [RB-Pli-06] and its measurements:
A better way to look at repetition & update rate would be to rephrase is as burst & update rates.
Lets start with some useful definitions:
- The burst rate is how many individual pulses occur during an acquisition.
- The update rate is how many acquisitions (measurements) you can take at a given burst rate.
- A burst is comprised of 10 kHz modulated pulses lasting approximately 500 ns.
- An individual acquisition can be comprised of anywhere from 1 to 255 bursts (tied to maximum acquisition count, address 0x02; default value is 128).
- The burst rate is a combination of the maximum acquisition count and the correlation record maximum signal peak.
- If the return signal is strong (target is either very reflective or at a short range) the acquisition can terminate before the maximum acquisition count value.
Therefore, the update rate varies based on settings (such as maximum acquisition count) and signal strength (due to target surface, distance, etc.).
By reducing the maximum acquisition count, the update rate can be increased. In the case of the LLV3 the maximum update rate can be greater than 500Hz and it can have a maximum update rate greater than 1 kHz.
Of course nothing is free. The penalty associated with reducing the maximum acquisition count to reduce the duration of acquisitions is that the sensor has reduced sensitivity and therefore reduced effective maximum range.
It should be noted that near or at 1 kHz update rate, the LLV3 would have a severely limited range, most likely only a few meters. If you need a very high refresh rate with a useful range, I would recommend instead to use the LLV3HP [RB-Pli-17] which has faster signal processing and can work properly at faster update rates.
Conversely, increasing the maximum acquisition count will increase sensitivity and allow operation at greater ranges but will most likely lower the update rate due to the increased acquisition duration.
As mentioned above, the laser (905 nm wavelength) sends 10 kHz pulses.
I hope this clears up all the details concerning those values!
Sincerely,
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