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EVM430-FR6047: Clamp transducers show good zero water flow ADC capture, but the ADC capture is not centered at zero

Anthony Davidson
Prodigy 90 points
Part Number: EVM430-FR6047

Tool/software:

I am trying to set up the EVM430-FR4067 with clamp on transducers. These are the details:

  • 1 inch PVC pipe, OD = 33.4 mm, ID 24.31 mm
  • jiakang transducers, the same ones used in SLAA949 (1 MHz, 50 deg angle)
  • tried placing transducers in the both the Z configuration and the V configuration

I have adjusted the gain to get a good signal, and for zero water flow the ADC captures look okay to me. But the captures are not centered around zero like they are in SLAA949. What does this mean? In other words, can I still proceed to measure water flow or do I need to change some of the MSP430 parameters, and if so, which ones.

These are my zero flow captures... (the left picture is transducers in the Z configuration, the right picture is in the V configuration.)

   

I haven't tried running the water yet to actually measure the flow.

  • +1
    TI__Genius 10550 points

    Hi Anthony,

    Are you using a very high programmable gain? If so, then the DC offset is pretty typical. If you are getting good readings at zero flow, I would encourage you to try testing at various flow rates to see if you still get good readings. If so, then great! If not then you can try adjusting your approach.

    We do have a feature called DC Offset Cancellation that you can enable that will cancel out the DC offset when the algorithm is running to calculate time of flight values. I will say, the DC offset cancellation is applied after the ADC capture, so when you enable it you should not see a difference in the ADC capture data shown in the GUI.

    You can read a bit about a similar case in this thread. It is also briefly described in figure 3-1 of the gas sensing reference design document. While that document is for gas sensing the DC Offset cancellation can still be used.

  • 0 in reply to Dylan OBrien
    Prodigy 90 points

    Yes, I am using a PGA setting of 22.8 dB.

    I read through your suggestions and was able to get it working. Thank you!!

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