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AD5933 measurement problems

Question asked by jferch on Feb 5, 2014
Latest reply on Feb 5, 2014 by musach

Hi everybody,


I made a circuit board with the AD5933 and a MSP430F1612 to measure high impedances. I power and control the circuit by USB and process the data with MATLAB. Communication is working just fine, but I'm having trouble measuring impedances. When I calibrated the AD5933 with a 500kOhm resistor and want to measure an unknown impedance (1MOhm) with the formula in the datasheet, I'm just getting rubbish as results like 400kOhm at 10kHz to 700kOhm at 100kHz. When i measure the Rcal again it works great. I'm running at 3,3V VDD RFB is 300kOhms. Do you guys have a clue what's wrong? If you need any code or the schematic/layout please let me know. Any help is highly appreciated!