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# AD5933 4-Electrode configuration for human body thoracic impedance measurement(0-60 ohm)

1.Please suggest the circuit diagram for 4-electrode configuration for human body thoracic impedance measurement range 0-60 ohm using ad5933

2.I want inject ac current 200uA at 100khz  ...please suggest the Resistor and capacitor value in the circuit diagram

3.Two electrodes for injecting the current and  another two electrodes for sensing the voltage

4.I want operate the circuit at single power supply

5.I have referred the link: AD5933 4 Wire Configuration for low impedence (< 50 ohm) but there is no clarity in the diagram.Please suggest the circuit diagram for 4-electrode configuration for human body thoracic impedance measurement range

• Hi,

1- the AD5933 cannot measure DC (0ohms), anyway, the measurable range depends on the inamp gain.

As suggesting a circuit,

Many approaches... but I recommend this one. I used and works fine... I need to check the exact part numbers,

2- at the output of the picture, transmitter have a cap and resistor,

Cap whatever value, just block DC

NOTE- the feedback resistor in the opamp should be large >1Mohms

If you are using your circuit in SS, you must add a RC in the inamp, to bias the signal.

Regards,

Miguel

1.can you suggest the exact part no

3. RC value for biasing the INAMP

4.C blockdc  value=?

5. i am using Rcal =20ohm (human body impedance range 1-60 ohm) is it right?

6. selection of INAMP and gain resistor value

7. opamp part no

8.I am using this circuit for the impedance cardiography

• Hi Sanjay,

DC Block capacitor (transmit stage) = 22 nF

Yes you are right, Rcal value = 20 Ohms will be for 1-60 Ohm impedance range

INAMP: you may use AD8220 for this.

Use Vdd/2 as reference for AD8220

Set the input resistor value and the gain resistor value to 2kOhm. Other values are shown below:

Cheers,

Ivan

• Thanks for your suggestion, I have done the experiment using this circuit

I am able read the Thoracic impedance within range using 4 electrode system(Injecting current Irms=1ma)

1.I am not able to monitor ECG  (using ad8232) along with Thoracic impedance circuit (Analog device suggested circuit)

2.if i connect the current injecting electrode to human body ecg is fully noise and there is no ECG waveform characteristics

3.if i don't connect the current injecting electrode to human body ecg waveform is proper.

4.please suggest me a circuit to monitor ecg and thoracic impedance together with out any noise.

5.please suggest me a circuit to isolate ecg and thoracic impedance circuit.

• Thanks for your suggestion, I have done the experiment using this circuit

I am able read the Thoracic impedance within range using 4 electrode system(Injecting current Irms=1ma)

1.I am not able to monitor ECG  (using ad8232) along with Thoracic impedance circuit (Analog device suggested circuit)

2.if i connect the current injecting electrode to human body ecg is fully noise and there is no ECG waveform characteristics

3.if i don't connect the current injecting electrode to human body ecg waveform is proper.

4.please suggest me a circuit to monitor ecg and thoracic impedance together with out any noise.

5.please suggest me a circuit to isolate ecg and thoracic impedance circuit.

• Hi Sanjay,

I do not think you can measure thoracic impedance and perform ECG measurements simultaneously since the current source from the impedance measuring circuit will act as a source of disturbance to the ECG circuitry which might explain why ECG waveform characteristics are not seen.

We advise you to consider taking a look at ADAS1000 as front end ECG and for thoracic impedance measurement.

Cheers,

Ivan

• Hi

Thanks for your suggestion, I have done some experiment for getting ecg along with thoracic impedance

1.if i power ecg (using ad8232) circuit from separate power supply ecg circuit is working fine along with thoracic impedance circuit(thoracic impedance circuit power supply is different. its a dual power supply).

2. Ecg and thoracic impedance circuit ground points are different (they are not shorted).

3.please suggest me the  isolation circuit to separate the power supplys and ground plan of  ecg circuit and the thoracic impedance circuit to get proper ecg wavefrom.

4.i want to power the ecg and thoracic impedance circuit circuit from the  same power supply.