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WEBENCH® Tools/MSP430FR6047: DTOF values are off by Constant factor

Shishir Pali
Prodigy 145 points
Part Number: MSP430FR6047

Tool/software: WEBENCH® Design Tools

Hello,

I have been done some experiments for testing on a pair of Audiowell senor the ultrasonic sensor using  MSP430FR6047 board, to check the reliability of these sensors for non-invasive flow metering application. While observing the result it came to my notice that the DTOF shown by MSP430 GUI is off by a constant factor of 3.35 approx. when compared with actual DTOF. 

Velocity (m/sec)  Theoretical DTOF (psec) MSP GUI DTOF (psec) Off by factor
0.6287 24168.57 6986.5 3.459324411
0.569 21867.73 6418.58 3.406942034
0.536 20601.33 5818.8 3.540477418
0.442 16972.12 5009 3.388325015
0.3794 14583.3 4361.64 3.343535918
0.334 12840.53 3918.2 3.277150222
0.29832 11466.59 3375.93 3.396572204
0.2241 8611.91 2647.7 3.25260037

For calculating Actual DTOF = 2 *L* V / C^2 is used 

where,  L - acoustic length traveled by the wave i.e. 0.103 m as per my setup.

    V - Flow Velocity

    C - Velocity of the sound wave in water i.e. 1450 m/sec.

Is there some inbuilt constant setting in GUI of MSP430FR6047 which is effecting the DTOF readings? What the way to change the constant?

  • 0
    TI__Mastermind 27675 points

    Hi Shishir,

    There shouldn't have a inbuilt constant something in the GUI.

    In fact, I couldn't figure out the throretical DTOF result in your table based on your data. For example, at v = 0.6287m/s. DTOF = 2 * 0.103 * 0.6287 / (1450)^2 = 61599ps. which is not 24168.57ps in your table. Can you check on it what we are missing here? 

    Best regards,

    Cash Hao

  • 0 in reply to Cash Hao11
    Prodigy 145 points

    Hi Cash,

    In previous mail, by mistake i have provided the wrong  L- acoustic length i.e. 0.103 m the correct value of L = 0.04041 m. If the GUI don't have any factor then is if possible that the firmware might be having it?

  • 0 in reply to Shishir Pali
    TI__Mastermind 27675 points

    Hi Shishir,

    I think neither the GUI nor the software has a inbuilt constant on calculating dTOF.

    Can you check how you get the V - flow velocity data? Are you getting it from the volume flow rate?

    Best regards, 

    Cash Hao

  • 0 in reply to Cash Hao11
    Prodigy 145 points

    Hi Cash,

    The V- Flow velocity data is correct since it's given a industrial meter, and i have cross-validated it with volume and time measurement method.

  • 0 in reply to Shishir Pali
    TI__Mastermind 27675 points

    Hi Shishir,

    I might suggest you to check again on the flow velocity. 

    Because if you get it from the volume flow rate in LPH(liter per hour). There is a constant factor 3.6 when you get m/s from LPH.  It is similar to what you get in the table.

    Best regards,

    Cash Hao

  • 0 in reply to Cash Hao11
    TI__Mastermind 27675 points

    Hi Shishir,

    Does it solve your issue? 

    Best regards,

    Cash Hao

  • 0 in reply to Cash Hao11
    Prodigy 145 points

    Hi Cash,

    I cross-checked it again as you suggested, all the v flow still data holds good. In fact after studying Cross-correlation documents of MSP430 (attached), on pg 6. it's mentioned that "for the correlation is computed over few points leading to a low-power implementation. 

    To ensure that Z0 is the maximum point, the correlation peak runs through a search algorithm sequentially computing the three adjacent correlation terms (Z–1, Z0, and Z+1) until it finds the maximum Z0 that is larger than Z–1 and Z+1 and the earlier correlation terms. The search window for finding the correlation peak can be set using USS_ALG_NUM_CYCLES_SEARCH_CORR in USS_userConfig.h or ussAlgConfig.numCycleSearchCorrPeak. Typically, only an additional 1 or 2 adjacent correlation points are computed in addition to the 3 correlation points."

    Is there a way, to make changes in the Algorithm so that it computes the correlation overall points?  without worrying about power consumption.

  • 0 in reply to Shishir Pali
    TI__Mastermind 27675 points

    Hi,

    I need some time to check on that.

    So you mean you do not care about the power consumption at all?

    Best regards,

    Cash Hao

  • 0 in reply to Cash Hao11
    Prodigy 145 points

    Hi Cash,

    yes, I really do not care about power consumption at all. It will be a great help if you can provide the above mentioned.

    Shishir

  • 0 in reply to Shishir Pali
    Prodigy 145 points

    Hi Cash,

    Also, one more thing I came across while reading the TI manual. and comparing the ADC capture acquired by me (best possible capture after fine tunning the results vs ADC capture shown in TI manual. It can be seen that my capture is a crest and trough kind of pattern. Can this be the reason which might be effecting the signal processing? What measure should i take to get a similar ADC capture as TI paper? 

  • 0 in reply to Shishir Pali
    TI__Mastermind 27675 points

    Hi,

    Sorry for the late response because of the Chinese new year and 2019-nCoV here.

    Your ADC capture looks like a secondary reflection signal to me. The SNR is poor. It is going to influence the result. You need to get a similar ADC capture here.

    Best regards,

    Cash Hao