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EVM430-FR6047: Offset in ADC-Capture

Pcat
Prodigy 10 points
Part Number: EVM430-FR6047


Hi

I'm trying to do some water flow measurements with clamp-on Ultrasonic transducers. As you can see in the Screenshot, I have a large offset in the ADC-Capture Signal. Can you explain why and how I can reduce this offset?
I think that the uncertainties in the measurements are because of this offset. Is this true?

Thank you and best regards

P

  • 0
    TI__Expert 7365 points

    Hi P,

    The DC-offset of the ADC capture is dependent, to some extent, on the PGA setting in the device. The offset is larger for larger gain setting of the PGA module. What is the PGA setting when you are obtaining these ADC captures?

    1. You should reduce the "Gap between pulse start and ADC capture (us)" by a few us. You can look at Figure 9 of the Quick start guide for water flow meters (http://www.ti.com/lit/slau810) is a good representative waveform for the start of the ADC capture.

    2. I also suggest increasing the capture duration. Figure 9 is also a good representation.

    3. To reduce the impact of the DC-offset of the ADC capture, you can enable DC-offset estimation and cancellation. This can be done by enabling below defines in USS_App_userConfig.h:

    #define USS_APP_DC_OFFSET_CANCELLATION_ENABLE

    /*! Defines the Interval for estimation of DC Offset */
    #define USS_APP_DC_OFFSET_CANCELLATION_INTERVAL (0) // -> Set this to a large positive value

    The USS_APP_DC_OFFSET_CANCELLATION_INTERVAL represents the # of measurements between DC-offset estimation. If the PGA setting does not change much, this can be set to a large positive value, say, 1000 or so.

    Srinivas

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