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More Info. about the sound speed in different DEF concentration

user4737083
Prodigy 30 points


Hi guys,

recently I use my TDC1000-C2000 to test the DEF concentration,  the TDC 100 spec. only give the sound speed in some concentration at the room temperature.

So I wonder whether you have more information about the speed in more concentration at different temperature? do you have any test data about it to share?

The accuracy given in the spec. is 0.5% with only 5.08 cm distance, it seems amazing for me, since the speed difference between DEF 32.5% and 32% is only 0.75 m/s, which is only around 0.05% refer to the 1630 m/s.

regards,

Charles Xia

  • 0
    TI__Mastermind 21685 points
    Charles,

    We don't have speed of sound variation with temperature at different concentration. That table 56 in Data Sheet shows speed of sound variation over different concentration at room temperature when measured in a test cell of fixed width of 2.54cm (hence total tof distance of 5.08cm). High resolution timer of C2000 is used to calculate the TOF which is then used to calculate the speed of sound.

    Thanks,
    Vishy
  • 0 in reply to Vishy Viswanathan
    Prodigy 30 points
    Hi Vishy, thx for ur reply.

    so u mean the high accuracy is because of the high resolution timer? but it seems that the resolution and accuracy don't have too much direct relation, right?

    PS: I got a initial value around 39μs with the fault configuration when no liquid is in my tank. does it mean the dead zone or I did some mistake?
  • 0 in reply to user4737083
    TI__Mastermind 21685 points
    I think the difference in TOF between 32% and 32.5% DEF is 16.3ns. You need a timer with ps resolution to measure these small differences. C2000 high resolution timer has a resolution of about 300ps and so can measure this time difference.

    DEF Measured Speed of Sound TOF
    (m/s) (us)
    32.5% 1630 5.08/1630 = 31.1656us

    30% 1629.15 5.08/1629.15 = 31.1819us


    Difference in TOF = 31.1819 – 31.1656 = 0.0163us = 16.3ns

    Are you using the level_fluid_test cell? Default registers are setup for level measurement (TX1). When there is no water, there is reflection at the acrylic to air boundary and that's what you are seeing I guess. In default register setup, the device is in standard tof measurement mode where the receiver turns on after the transmit is complete. See DS section 8.4.6.2

    thanks,
    Vishy