AD5933 Eval Board phase measurement at lower frequencies

Hello,

I am using the AD5933 Eval Board to measure a charateristic phase shift of an impedance sensor. Between 5 and 100 kHz I get decent values with MCLK setting to 16 MHz.. For measuring at lower frequencies (1-5 kHz) I set MCLK to 2 MHz but now my values got implausible.

At 2 MHz MCLK and lower frequencies i get a new phase mimium at -7°altough the values should extend the curve measured at higher frequencies.

I am following the procedure for "measuring the phase across an impedance" and "measuring at lower frequencies" from the user guide.

I'm only using the internal oscillator.

Is it possible that the measured phase angle depends on clock frequency? It should not right?

Thanks for helping me,

mb

  • From your description it is not quite clear what the issue is. When you calibrate with a resistor you should see only the phase introduced by the system.Could you provide a bit more details such as the Rfb value, Vexc, PGA gain and other settings? What Rcal value you are using and what is the impedance range of your sensor?

    I'm only using the internal oscillator

    It should be 16.776 MHz with the internal oscillator, how did you get 2 MHz without the external oscillator?

    Is it possible that the measured phase angle depends on clock frequency? It should not right?

    The measured phase should not depend on the clock frequency.

    Best of luck!