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About AD5933 Accuracy

Question asked by Laliberte on Dec 1, 2014
Latest reply on Dec 1, 2014 by musach

Hi, All.

 

I have to measure the impedance of the capacitor using the AD5933 evaluation board.

Accuracy of the data sheet(Total System Accuracy 0.5%) as can not be obtained.

 

<ex.>

DUT Capacitor(Z)=100pF

Frequency=10kHz,100kHz

Calibration Resistor=100kΩ(10kHz),10kΩ(100kHz)

Result Capacitor=96.2pF(10kHz),94.1pF(100kHz)

Result Impedance=16.5kΩ(10kHz),16.9kΩ(100kHz)

C Meter(Master)=96.7pF(10kHz),95.7pF(100kHz)

 

At high frequencies(100kHz), the measurement error is large compared to the master unit.

As there is Rcal,RFB of Calculation in AN-1252, in the case of known impedance, it is possible to measure by adjusting the calibration resistor, I think to be able to approach the true value.
Please advice on how to reduce the error (less than 1%) in addition to the adjustment of the calibration resistance in case of measuring the unknown DUT.

 

<Evaluation Board Condition>

System Clock:External clock

Output Excitation:Range1:2Vp-p

PGA:Gain=X1

Calibration Impedance:R only

DDS Setting:X1

Calibration Gain Factor:Multi Point

RFB,RCAL is same register

 

Best Regard,

Hara

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