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Original question:

EVM430-FR6047: Jumping dTOF

EVM430-FR6047: tuning!

Laurent van Poppelen69
Expert 1020 points
Part Number: EVM430-FR6047
Other Parts Discussed in Thread: TIDA-01486

Hi,

we are experiencing something alike. We have two channels with different distances, 340 us and 440 us, which complies with the soundspeed in water! We use 1 Mhz and have amplified the Tx/Rx using a modified TIDA-01486. The 340us is very stable and shows no jumping and, actually shows zero flow when here is no flow! The 440us does jump however! We like to know what steps to perform, which parameters, for tuning this? Our signals have ampltudes around 1200 with the capture.

Could you provide suggestions and/or literature?

rgds,

Laurent

2M Engineering Ltd

  • 0
    TI__Expert 7365 points

    Hi Laurent,

    The tuning procedure of the parameters is the same for both transducer pairs. The quick start guide for water flow meter is a good document that walks you through the steps (https://www.ti.com/lit/pdf/slau810). 

    The 1200 ADC codes is higher than what is suggested. Figure 4-5 has an example ADC waveform capture and the suggested ADC codes of 900. The text on page 6 with regards to the PGA setting has the following:

    ----------------------------------------

    The "GUI Based Gain Control" controls the gain of the integrated PGA. Set this parameter to give an ADC capture of no more than ±900 ADC counts in the ADC capture tab. Although the system should be operable with signals down to ±150 ADC counts, setting the gain to give higher ADC counts reduces the standard deviation in measurements.

    ----------------------------------------

    Laurent van Poppelen69 said:
    The 440us does jump however!

    What does it mean when you say, it "does jump"? The DToF or AToF values are not stable even though the flow is stable or zero flow? What kind of jumps do you see? Can you see the behavior after reducing the gain so that you get closer to 900 codes?

    Srinivas

    Edit: Corrected to Page 6 where the above text is in the document.

  • 0 in reply to Srinivas Lingam
    Expert 1020 points

    Hi, we fixed that but still have another issue.

    This is a picture of our 340us channel pair:

    Here shown are ups and dns at a distance of 437us for a sensor pair thats placed half way the height of our circular pipe. We get these captures:

    UPS distortion at the beginning 

    and DNS distortion at the beginning

    Could this be reverberation?

    Which would imply a necessary change of the positioning of the sensors!

    Also, should we calibrate the different Bias offsets of UPS and DNS to match them to '0'?

    rgds,

    Laurent

  • 0 in reply to Laurent van Poppelen69
    TI__Expert 7365 points

    Hi Laurent,

    Laurent van Poppelen69 said:
    Could this be reverberation?

    That is a possibility. One option to check if this is causing the distortion is to increase the gap between UPS & DNS excitations ("UPS and DNS gap"). It is discussed in page 7 of the Water flow meter guide (https://www.ti.com/lit/pdf/slau810). 

    But it is strange that it occurs on UPS in the 1st plot and DNS in the 2nd plot. The DNS in the 1st plot and UPS in the 2nd plot look good. Does this change randomly or is there some pattern to it?

    Laurent van Poppelen69 said:
    should we calibrate the different Bias offsets of UPS and DNS to match them to '0'?

    Yes, you should enable the DC Offset estimation and cancellation to ensure the DC offset of the UPS and DNS ADC captures are close to zero. Usually, the DC offset is higher with a higher setting of the PGA.

    Srinivas

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