Hi, I have a few clarifications about the instructions provided on the Impedance Measurement with AFE4300 regarding using the AFE4300 in FWR mode for calculating bio-impedance. I'm following the instructions for SF-BIA implementation described in the document. I would appreciate clarifications on the following items:
- For step #3, "measure the voltage across Rx and Ry from the AFE4300 in FWR mode", how can I ensure that I am doing so in "FWR" mode? Are there specific registers we need to be reading from?
- What are the range of ADC codes that should be read at a DAC frequency of 64 kHz? What happens if we are calibrating at 50 kHz? I'm trying to figure out if the hardware is outputting correct resistance values, and was wondering how can I determine the range of acceptable ADC codes? Or are there other ways I can validate the ADC codes for my reference resistors are correct?
- I see that the instructions state to "Set the AFE4300 DAC frequency to 64 kHz". After I've used this frequency to compute the calibration between two reference resistors, am I then able to calculate impedance at a different frequency (i.e. 50 kHz)? I'm asking because recent research has suggested that measuring resistance at 50 kHz is adequate for SF-BIA, yet I don't see a reference to measuring against a separate frequency after the "Set the AFE4300 DAC frequency to 64 kHz" step.
- What are the constraints of the "sample impedance network" that we should test against? Does it necessarily have to be a series RC impedance network, and should expect greater errors if this wasn't the case?
- The instruction manual also says: "the series RC impedance network is a 549.5-Ω resistor in series with a 4% accurate 0.111-µF capacitor. In theory, the magnitude of this sample network should be 549.96 Ω and the ADC code is 7151". Could you help me understand how you calculated the theoretical magnitude of the network and the expected ADC value here?
Thank you so much for your help!
