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Original question:

LDC1101EVM: LDC1101EVM

LDC1101EVM: How to test the output signal of INA and INB with other measurement system?

user5924868
Prodigy 10 points
Part Number: LDC1101EVM

Good Morning,

I just got my LDC1101EVM recently, and have met some questions about measuring the voltage between INA and INB with my oscilloscope.

The output wave is in the figure below.

It looks like noise or amplitude modulation occurred. I wonder why that happens.

I firstly ruled out the possibility of environmental interference.

Then I found the frequency output in GUI  changed. 

The oringinal signal (before the oscilloscope involved, as the figure on the left) is stable and ideal.

While the signal with error is unstable(after the oscilloscope involved, as the figure on the right).

Is there something wrong with the oscillation of the coil?

Is there any way to eliminate such error?

What can I do to get ideal signal output of INA and INB in measurement system?

Thank for your help,  

Dylan

  • 0
    TI__Genius 11015 points
    Hi,

    We have received your question & our application engineer will answer this question shortly.
  • 0
    TI__Mastermind 23810 points
    It looks like the parasitics from your oscilloscope probe is impacting the measurement. You can try using a lower capacitance probe with a short ground connection (to minimize parasitic inductance). Or you can try taking the measurement through a 1kOhm resistor.

    The amplitude modulation depends on which mode you are using. For Rp+L, it is normal for there to be amplitude variation. For HRL, it is normal for there to be some settling time when it first starts oscillating, but then the amplitude should be more stable. However, if the metal target is changing, then the Rp of the sensor will also be changing, which means that the amplitude will also change.

    Thanks,

    -Clancy