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EVM430-FR6047: DToF measurement Error zero flow

Maik Bruhn
Prodigy 170 points
Part Number: EVM430-FR6047

Hi,

I'm using the EVM430-FR6047 for measuring the volume flow rate. 
In my first test is measure the AbsToF under zero flow conditions. Here sometimes an error occurs. Error code 135: 

01/25 02:36 PM Algorithm 135 DToF - Shift value was greater than maxSampleShift

Why does the error occur randomly? The ADC capture looks fine all the time. 
Do you have an explanation and how can I fix it?

Thanks.

Maik Bruhn

  • 0
    TI__Expert 7365 points

    Hi Maik,

    That should not happen if the ADC capture is normal and the configuration is ok. Are you still using the default setting for USS_ALG_MAX_SAMPLE_SHIFT in USS_userConfig.h?

    #define USS_ALG_MAX_SAMPLE_SHIFT 20

    Is the Envelope Crossing Threshold set according the suggestion in section 4.2.2 of the Water flow meter quick start guide (https://www.ti.com/lit/pdf/slau810)? 

    Have you confirmed that when you log the continuous ADC captures, the ADC captures are not encountering a break?

    Srinivas

  • 0 in reply to Srinivas Lingam
    Prodigy 170 points

    Hi Srinivas,

    The ADC capture looks okay but is a bit to small at max. amplification. We will today integrate the Booster Pack to increase excitation and amplification. Max. ADC value is about 700
    Yes, the USS_ALG_MAX_SAMPLE_SHIFT is still default.

    The envelope crossing treshhold is set to 11. 

    There doesn't occur any break in the ADC capturing.

  • 0 in reply to Maik Bruhn
    TI__Expert 7365 points

    Hi Maik,

    700 ADC codes should be sufficient. How is the signal integrity around 77 ADC codes? The envelope crossing threshold of 11 indicates the algorithm is locking to the tone around 77 ADC codes. Did you make sure that 11 meets the following suggestion from section 4.2.2 of the Water flow meter quick start guide (https://www.ti.com/lit/pdf/slau810) - "Set this threshold to lock onto the earliest lobe peak that is above the noise."?

    Can you also post the image (and/or the .csv file) of the ADC waveform capture?

    Srinivas

  • 0 in reply to Srinivas Lingam
    Prodigy 170 points

    Hi Srinivas,

    I checked the data and sometimes the noise level is higher than the threshold. So I changed the Threshold value. 
    Is there a way to increase accuracy of the ToF measurement when the noise level is so high?

  • 0 in reply to Maik Bruhn
    TI__Expert 7365 points

    Hi Maik,

    You can increase the number of pulses to see if the overall signal level increases. The signal level does not increase much beyond a certain number of pulses. So it depends on what you are currently using.

    It also depends on the characteristics of the noise seen at the beginning of the signal. Will some filtering help improve the SNR here?

    Another option is to increase the threshold so that it locks on to some later pulse. It all depends on the relative SNR in the initial portion of the signal and your current configuration.

    Srinivas

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