Using electrodes with ADuCM350 4 Wire BioZ board

Hi Marian,

What frequency did you use for this measurement? Did you change any other parameters?

Measuring the AFE output using a standard oscilloscope probe will lead to errors in the measurement. The additional load of the scope probe will affect the measurement. If you want to measure the AFE response, you should measure outside the loop (e.g. the TIA output, TIA_O) or use active scope probes (a force-sense measurement).

Rgds,

Eoghan.

Can you provide some information about the electrodes that you are using please?

What type of electrodes are they? (e.g. metal, rubber; can you name the manufacturer?)

What size are the electrodes?

Where on the body are the electrodes placed when taking the measurement?

Any other information about the electrodes or the measurement that might be helpful?

Can you please provide some more information on the circuit that you are using? We need to investigate if any of the circuitry that you are using could affect the measurement loop of the ADuCM350.

Can you try this in a simple 2-wire measurement mode initially? This is a less complex measurement and would be a good starting point. Please reference the ImpedanceMeasurement_2Wire example, or use the 2 Wire measurement option in the EKSP software.

Hi Eoghan,

today I changed on board RTIA on 2.2kohm, RLIMIT on 1kohm and RG on 47kohm.

RCM1 and RCM2 are still 10Mohm and CISO1 - CISO4 are 47nF also.

In application I changed RTIA on 2.2kohm and IN-AMP GAIN on 2.05.

I used different frequencies like 500Hz, 1kHz, 10kHz, 25kHz, 50kHz......

Also I tried to changed amplitude from 200mV to 600mV.

I do not know.... the phase output is strange (but -154 is not good at all) and the magnitude is sometimes good and sometimes bad.

If you have any idea what I am doing wrong, please help me.

Thanks in advance

Best regards

Marian

At this time I am using wires and crocodile clips to connect on the test board with circuits.

This circuit is simulating the human tissue. I want to verify the output from ADuCM350 with RLC meter.

Do you have some kind of application note for 2-wire measurement? Because I have found only for 4 wire.

Or may I let the connection of the circuit as in 4 wire measurement and try only 2-wire option in EKSP?

OK, I tried to measure with 2-wire mode.

I attached output from simulation and also the circuit that I measured.

And here are the output from ADuCM350. I used EKSP SW.

A 2-wire measurement follows all of the same criteria as a 4-wire (non-isolated) measurement, except that the feedback nodes (P and N) are connected to D and T internally to the AFE instead of at the sensor. Therefore, 2-wire measurements are inclusive of access impedance, but give good relative accuracy. Also, the external in-amp is not required for a 2-wire isolated measurement. For a 2-wire measurement using the BioZ board, you should ensure that you remove the connection to the in-amp (LK9 and LK10)

For the results above, what exactly are you measuring? Is it the circuit shown; 470 ohm + (1 kohm || 10nF)? Is there any access impedance? Is there a current limiting resistor in series? Have you implemented this circuit on the BioZ daughter board or on another piece of hardware? Do the ideal results on the EKSP match the measured results?

This white paper may be helpful when considering bio-impedance applications:

Bio-Impedance Circuit Design for Body Worn Systems - Jose Carlos Conchell

Hi Eoghan,

let me get this straight. So I have to use R_access resistor anyway? If I will measure on circuit or human body? It will not be any impact  when I will measure on human body?

I will try it and let you know.

Best regards

Marian