• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 30 subscribers
  • Views 554 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

PGA460-Q1: About the error of short distance measurement(20cm-50cm)

Masuda
Prodigy 40 points
Part Number: PGA460-Q1
Other Parts Discussed in Thread: BOOSTXL-PGA460, PGA460
Hi,
I am using BOOSTXL-PGA460 EVM for my project. I tested the EVM with the Murata MA58MF14-7N.
My product demands object sensing in the range of 20cm-50cm. The object is a flat(such as wall).
Doing some tests here on the bench, There was a bit of a discrepancy(about 3cm-4cm).
Would there be any way to solve this distance error.
Are the results within the margin of error.
The GUI Echo data dump capture image is shown below:
1)Object is physically at 50cm:
2)Object is physically at 40cm:
3)Object is physically at 30cm:
4)Object is physically at 20cm:
The configuration diagram is shown below.
1)General
Please find attached here with my configuration file also.
Fullscreen GRID_USER_MEMSPACE-2020-03-06_185823.txt Download 
;GRID_USER_MEMSPACE
00 (USER_DATA1),00
01 (USER_DATA2),00
02 (USER_DATA3),00
03 (USER_DATA4),00
04 (USER_DATA5),00
05 (USER_DATA6),00
06 (USER_DATA7),00
07 (USER_DATA8),00
08 (USER_DATA9),00
09 (USER_DATA10),00
0A (USER_DATA11),00
0B (USER_DATA12),00
0C (USER_DATA13),00
0D (USER_DATA14),00
0E (USER_DATA15),00
0F (USER_DATA16),00
10 (USER_DATA17),00
11 (USER_DATA18),00
12 (USER_DATA19),00
13 (USER_DATA20),00
14 (TVGAIN0),44
15 (TVGAIN1),44
16 (TVGAIN2),44
17 (TVGAIN3),08
18 (TVGAIN4),64
19 (TVGAIN5),9A
1A (TVGAIN6),98
1B (INIT_GAIN),40
1C (FREQUENCY),8F
1D (DEADTIME),80
1E (PULSE_P1),06
1F (PULSE_P2),10
20 (CURR_LIM_P1),0E
21 (CURR_LIM_P2),71
22 (REC_LENGTH),19
23 (FREQ_DIAG),00
24 (SAT_FDIAG_TH),EE
25 (FVOLT_DEC),7C
26 (DECPL_TEMP),4F
27 (DSP_SCALE),00
28 (TEMP_TRIM),00
29 (P1_GAIN_CTRL),00
2A (P2_GAIN_CTRL),18
2B (EE_CRC),3B
40 (EE_CNTRL),00
41 (BPF_A2_MSB),8A
42 (BPF_A2_LSB),0C
43 (BPF_A3_MSB),F9
44 (BPF_A3_LSB),A5
45 (BPF_B1_MSB),03
46 (BPF_B1_LSB),2D
47 (LPF_A2_MSB),7E
48 (LPF_A2_LSB),67
49 (LPF_B1_MSB),00
4A (LPF_B1_LSB),CD
4B (TEST_MUX),00
4C (DEV_STAT0),80
4D (DEV_STAT1),00
5F (P1_THR_0),44
60 (P1_THR_1),44
61 (P1_THR_2),44
62 (P1_THR_3),44
63 (P1_THR_4),55
64 (P1_THR_5),55
65 (P1_THR_6),9C
66 (P1_THR_7),D0
67 (P1_THR_8),72
68 (P1_THR_9),10
69 (P1_THR_10),63
6A (P1_THR_11),28
6B (P1_THR_12),30
6C (P1_THR_13),34
6D (P1_THR_14),3C
6E (P1_THR_15),00
6F (P2_THR_0),77
70 (P2_THR_1),77
71 (P2_THR_2),77
72 (P2_THR_3),77
73 (P2_THR_4),78
74 (P2_THR_5),88
75 (P2_THR_6),9C
76 (P2_THR_7),D0
77 (P2_THR_8),72
78 (P2_THR_9),10
79 (P2_THR_10),63
7A (P2_THR_11),28
7B (P2_THR_12),30
7C (P2_THR_13),34
7D (P2_THR_14),3C
7E (P2_THR_15),00
7F (THR_CRC),3A
EOF
Kindly help me in resolving this issue.
My best regards.
  • 0
    TI__Mastermind 27950 points

    user6295760,

    Does the TOF value in the datalog provide a more accurate result than the distance printed in the Ultrasonic Measurement Results Table?

    Let me also try to replicate these results to help offer a potential solution. Looking at your threshold, it is definitely possible for you to more quickly lower the level after decay so that you cut the echo peak closer to the base rather than the mid or peak segment. The default / GUI suggested "short" and "long" threshold maps are not the most optimal for very short range accuracy.

  • 0 in reply to Akeem Whitehead
    Prodigy 40 points
    Hi Akeem,
    Thanks for the speedy response.
    The datalog value in the utilities tab is as follows:
    1 - Object is physically at 50cm:
      Dist(m) : 0.527
      TOF     : 0B9C
     
    2 - Object is physically at 40cm:
      Dist(m) : 0.433
      TOF     : 0979
     
    3 - Object is physically at 30cm:
      Dist(m) : 0.340
      TOF     : 075B
     
    4 - Object is physically at 20cm:
      Dist(m) : 0.241
      TOF     : 0519

    I calculated distance based on TOF value on the condition that ultrasonic speed is 343[m/s]. The result is as shown below:
    1 - Object is physically at 50cm:
      TOF : 0B9C
            -> 2972[us]
            -> Dist[m] = 343 * 2972*10^(-6) / 2
                       = 0.5097[m]
    Thus, each distance was calculated
    40cm : 0.4159[m]
    30cm : 0.3229[m]
    20cm : 0.2238[m]

    Please let me ask some questions.

    (1)What is the unit of TOF? Microseconds?
    (2)Why does the TOF value provide a more accurate result than the distance printed in the Ultrasonic Measument Results Table?
    (3)Are the results based on TOF within the margin of error?
    My best regards.
  • 0 in reply to Masuda
    TI__Mastermind 27950 points

    Masuda,

    Responding to your questions:

    1. The time of flight values read from the Ultrasonic Measurement Result command are a 16-bit value representing microseconds.

    2. The time-of-flight is more accurate because this result is directly from the device, while the distance is based on the GUI's conversion of time-of-flight to distance. The TOF-to-Distance conversion includes additional factors, such as digital delay of the PGA460 and the burst time in an attempt to produce the most accurate conversion. For very close range detection, the GUI must be further optimized.

    3. The accuracy and margin of error is primarily dependent on where the threshold level and the echo envelope intersect. The closer the threshold level is to the noise floor, the more accurate the result. The accuracy tends to decrease if the echo appears in the ring-decay window, which is where very close range objects tends to sit.

  • 0 in reply to Akeem Whitehead
    Prodigy 40 points

    Hi Akeem,

    Thanks a lot for the information and your support

    Regards,