Movement Fast and Slow

Discussion in 'Respiration Sensor' started by Jun Ying, Jan 21, 2018.

  1. Jun Ying

    Jun Ying New Member

    Hello,

    What is the practical difference of those 2 data points? I know they are taken over 6 vs 15 seconds on a X4M200. How are they to be used to differentiate movements? Thank you.
     
  2. Charlie Shao

    Charlie Shao Moderator Staff Member

    Hi Jun,

    The movement metrics (MovementSlow and MovementFast) show the degree of movement as a relative number from 0 to 100 both for 5.14 cm intervals in the Detection Zone and for the entire Detection Zone. 0 means no Doppler cells above the detection threshold, while 100 means that all Doppler cells in the range interval are above the detection threshold.

    The movementfast is sensitive to massive motion like people walking or hand waving, while the movementslow reflects the tiny motion of chest or abdomen when people are still. The RPM is extracted from movementslow. You can get more detail from X4M200 datasheet.
     
  3. Jun Ying

    Jun Ying New Member

    Thanks Charlie. So that's the average of detection of the 6 and 15 seconds? So if i moved my finger for a second, then the it would say 45% for that second, but 0 for the other 15, yielding 3? Also, the 5.14cm interval is only 1 dimension, correct? Given it's a cone, further away from the sensor, less cells would detect, is that correct?
     
  4. Charlie Shao

    Charlie Shao Moderator Staff Member

    Hi Jun,
    Just to make it clear, the setting for baby is 6/15, for the adult is 6/20.

    I did not get your idea, if you are interested in this process, please refer to section 4.6.

    Yes, the radar can only see only one dimension, it can see the reflection from a sphere in front of its space. X4M200 can get one baseband complex data every 5.14cm, which can cover a range of 9.6m with 188 bins, but X4M200 only support up to 5.00m for reliability consideration. The reflection signal becomes weak when the distance increase. So you can always get baseband data every 5.14cm interval in the detection zone, not less, then no data output beyond this zone.
     
  5. Jun Ying

    Jun Ying New Member

    Thanks Charlie. I looked at all the documentation a few times. I have the following questions:

    1. the number is a percentage, correct? meaning 90 means 90% of the cells have movement in it.
    2. say the number is 90 for movement slow, does that mean in 20 seconds, every second 90% of the cells saw movement? meaning it's an average of every second in those 20 seconds.
     
  6. Charlie Shao

    Charlie Shao Moderator Staff Member

    1. Yes, 90 means 90% cell values are above the movement detection threshold.
    2. If you have tested X4M200 with XeThru Explorer, you are able to check the pulse-doppler matrix. Pulse-doppler Slow matrix is the doppler analysis result of last 20s radar data, it is updated every one second. So here 20s is not separated, it is doppler analysis result of data at former 20s.
     
    Last edited: Jan 25, 2018
  7. Jun Ying

    Jun Ying New Member

    Thanks. So it's a sliding window of 20 seconds of analysis. So say there are 100 cells, in the last 20 seconds, during second 1, 5 cells detected above threshold, in second 2, another 5 cells, until the 20th second. That would yield 100 cells total during the last 20 seconds. So the movement value for those 20 second is 100, not 5 (which is average taken sample at every second for 20 seconds), correct?
     
  8. Charlie Shao

    Charlie Shao Moderator Staff Member

    doppler.jpg
    movementslow.jpg
    Hi Jun,
    You are not correct. I think it is better to explain to you with this picture. This is pulse-doppler matrix slow, it is the doppler analysis result of the last 20s radar data. You can find that every range bin (from 0.39 to 3.06 with 5,14cm interval) has a Doppler analysis result contains frequency cells from -8.5HZ~8.5Hz, every cell will be compared with the threshold, the output is the percentage of cells above the threshold at every range bin, then we get MOVEMENT SLOW list.
     
    Last edited: Jan 26, 2018
  9. Charlie Shao

    Charlie Shao Moderator Staff Member

  10. Jun Ying

    Jun Ying New Member

    Thank you. I had the wrong mental model.

    Now onto another question: distance in the detection. The X4M200 gives a detection count and detection distances corresponding to the detection count. What is a "detection"? Is a foot and an arm potentially 2 different detections with distances?
     
  11. Charlie Shao

    Charlie Shao Moderator Staff Member

    Hi Jun Ying,
    where you found this 'detection count'? I am not quite sure the meaning of it.
    From the XeThru Explorer, you can find that X4M200 support DISTANCE output of CLOSEST moving target in the detection zone. When it detects the breathing of one still person in the detection zone, it will also start to output this person's distance.
     
  12. Jun Ying

    Jun Ying New Member

    Using your python wrapper, we are pulling detection count, and a number of cross sections size, distance, and velocity corresponding to the number of detection count.
     
  13. ahhjones

    ahhjones New Member

    Hi Charlie Shao,

    Just to be clear, is this to say that the relative proportion of doppler cells (0-100) detecting movement over the threshold is computed using the last 20 seconds of data for each individual bin? So, for example, at time t the relative number of cells over the threshold for a given range bin is calculated using the movement between t-20s and t?

    Thanks in advance for your help!
     
  14. Charlie Shao

    Charlie Shao Moderator Staff Member

    Yes, for the X4M200 respiration sensor:
    MovementSlow: Movements for the previous 20 seconds
    MovementFast: Movements for the previous 6 seconds
     
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