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Wrong result from AD5933EBZ with Rev.B software

Question asked by anya on Jul 11, 2018
Latest reply on Jul 12, 2018 by Snorlax

Dear Analog Devices Technical Support,

 

I am using the AD5933EBZ Rev.C to measure an unknown capacitor, the Labview programming software that I use is the “Rev. B” version, and I would be grateful if you could answer a few questions I have.

 

Question 1:

Does the Labview revision version need to be matched? If it does, where shall I find the “Rev. C” software? I could not find from the official website.

 

Question 2:

First of all, I tested the board to make sure it works fine. The steps follow the guidance from the specification “Evaluation Board User Guide UG-364” (page 6-7), which are:

1) Connect a resistor of RFB is 200KOhm, a resistor of Zunknown is 200KOhm.

2) MCLK: 16000000Hz. System clock: External. Start frequency: 30000Hz, Increment 2Hz, Number of increment 10. Output Excitation: Range1. Settling time cycles:15; DDS :× Click “Program device registers”.

3) Fill “200E3” in the Resistor value R1 blank frame. Choose “Resistor only C1” in Calibration Impedance mode. Calibration gain factor: “mid point frequency calibration”. After that, click “Calculate gain factor” to gain factor.

4) Click “Single measurement” to get the result and “Download the data”. The data matches with the 200KOhms-resistor.

 

Then, I changed the resistor of of Zunknown to 6.7KOhm, and the rest of setup does not change. I didn’t click the “Program device registers” or the “Calculate gain factor”. I just clicked “Single measurement”.  The result of impedance gives a Zunknown of 96.8KOhm, which is wrong.

 

Why this result was wrong? Should the Zunknown value be within a certain range comparing with the calibration resistor? If it does, how much is this range?

 

Question 3:

Afterwards, I measured a capacitor, steps follow the guidance from the specification “Evaluation Board User Guide UG-364” (page 6-7) as well, which are:

1) Mount a resistor of RFB is 200KOhm, a capacitor of Zunknown is 330pF.

2) MCLK: 16000000Hz. System clock: External. Start frequency: 30000Hz, Increment 2Hz, Number of increment 10. Output Excitation: Range1. Settling time cycles:15; DDS :× Click “Program device registers”.

3) Fill “330E-12” in the Capacitor value C1 blank frame. Choose “Capacitor only C1” in Calibration Impedance mode. Calibration gain factor: “mid point frequency calibration”. After that, click “Calculate gain factor”.

4) Click “Single measurement” to get the result and “Download the data”. In the Labview program plot, the phase remains at 0, which is apparently incorrect. In the Impedance data, when frequency is 30000Hz, Impedance is 16068Ohm, Phase is 0, Real axis is 4918, Imaginary is -19851 and the Magnitude is 20451Ohm. It seems that the Imaginary data and Real data can calculate out the Magnitude’s data, but according to the Phase’s data, the Impedance (16068Ohm) does not match with the Magnitude(20451Ohm). Shouldn’t the Magnitude correspond to the Impedance?

 

In the above description, I would like to ask:

      a) is there any step I did wrong? If I did, then in order to measure an unknown capacitor, which Calibration Impedance mode shall I choose?

      b) Comparing with the calibrated capacitor, how much of the Zunknown capacitor is able to be correctly measured?

      c) Also, I would like to add a time control function in the Labview program for measuring the result periodically, but I cannot open the block diagram of the program because it requires security username and password. Is there a way to add this time control function? Is there a version of this program that I can edit?

 

Those are all of my questions. I would be enormous grateful that if you could answer them. Thank you very much.

 

Kind regards,

 

Ya

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