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3 electrode EIS measurement using AD5940 EVAL ELCZ

Hello AD Team,

I have purchased AD5940 EVAL ELCZ board 

I want to perform EIS measurement for a 3 electrode system

Working electrode - Gold

Counter electrode - Platinum 

Reference electrode- Ag/AgCl (0.21 V vs Standard Hydrogen Electrode)

Calibration settings :

frequency range: 1KHz to 10Hz

Bias voltage: 300mV vs Ag/AgCl reference electrode

In the AD5940_examples code for impedance measurement , the method used was Sense electrode connected to AINx pins which was a 2 electrode system (WE :AINx and CE: CE0)

How do I modify this code to accommodate a 3 electrode system as given above ? What should be the switch matrix configuration ?

Kindly guide me through the process 

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  • Hi,

    Vzero is set by 

    AppIMPCfg.Vzero 

  • Hi,

    AppIMPCfg.Vzero  does not exist in Impedance.c and AD5940_Impedance project 

    Could you please check into this?

  • Hi,

    Can you search for AppIMPCfg.Vzero in Impedance.c

  • Hi,

    I think we both have 2 different version of Impedance.c . The one i have was downloaded from AD5940_example github.. Could you share your version ?

      

  • Hi,

    Thank you for that link.

    For our experiment we have to measure RzMag and RzPhase for a 3 electrode system

    Problem : The phase values must be in the range of 0 to -90 degrees , but the phase values were going shooting up and down going out of bounds.

    What can we do to get phase values within the range?

    I have added the settings we used below

    RcalVal Pwrmod LptiaRtiaSel LpTiaRf LpTiaRl HstiaRtiaSel ExcitBufGain HsDacGain DacVoltPP BiasVolt Vzero LpAmpPwrMod HstiaCtia HstiaDeRload HstiaDeRtia
    5000 AFEPWR_LP LPTIARTIA_6K LPTIARF_1M LPTIARLOAD_100R HSTIARTIA_5K EXCITBUFGAIN_0P25 HSDACGAIN_0P2 20 194mv 310mv LPAMPPWR_NORM 31 HSTIADERLOAD_OPEN HSTIADERTIA_OPEN

    The outputs obtained from AD5940 EVAL ELCZ are

    Freq Mag Phase Phase(Radians) Real Part Imaginary Part -Imaginary Part
    Freq:300.00 18598.55469 21.68462 0.3782761489 17283.68648 6868.800355 -6868.800355
    Freq:236.54 9125.26465 -19.72364 -0.3440679422 8590.435285 -3078.12874 3078.12874
    Freq:186.51 5342.30371 -41.27015 -0.7199348389 4016.604066 -3522.37146 3522.37146
    Freq:147.06 14166.83984 -84.70303 -1.477597301 1318.425081 -14105.35736 14105.35736
    Freq:115.95 672.85523 0.61284 0.01069065333 672.81678 7.193124988 -7.193124988
    Freq:91.42 119.63677 2.36565 0.04126745 119.5349136 4.935703227 -4.935703227
    Freq:72.08 724.7486 102.98277 1.79647721 -162.1770169 706.3704045 -706.3704045
    Freq:56.84 346.73135 145.50624 2.53827552 -285.5187328 196.7274314 -196.7274314
    Freq:44.81 425.25339 132.86993 2.317842112 -288.9487167 312.0081487 -312.0081487
    Freq:35.33 251.71271 -178.63466 -3.116182402 -251.6314513 -6.395394951 6.395394951
    Freq:27.86 172.66576 173.08084 3.019299098 -171.3761986 21.06331519 -21.06331519
    Freq:21.97 626.93933 -140.72044 -2.454789898 -484.7979112 -397.5222117 397.5222117
    Freq:17.32 365.97711 -62.2551 -1.086005633 170.553817 -323.8064863 323.8064863
    Freq:13.66 247.9153 -43.807 -0.7641887778 178.9809439 -171.5453809 171.5453809
    Freq:10.77 862.71643 13.38434 0.2334823756 839.3079909 199.6039452 -199.6039452
    Freq:8.49 804.01599 -41.06674 -0.7163864644 606.3756139 -527.9681118 527.9681118
    Freq:6.69 817.92841 -67.3604 -1.175064756 315.2977619 -754.7146515 754.7146515
    Freq:5.28 879.36475 91.00647 1.58755731 -14.73832771 879.2412327 -879.2412327
    Freq:4.16 356.60803 153.05237 2.669913566 -317.6687852 162.0365081 -162.0365081
    Freq:3.28 1278.87671 -7.29908 -0.1273283956 1268.523801 -162.3976756 162.3976756
    Freq:2.59 1050.96765 54.64161 0.95319253 608.5977899 856.8207114 -856.8207114
    Freq:2.04 408.53467 -176.60107 -3.080707554 -407.7776858 -24.85830897 24.85830897
    Freq:1.61 595.61542 -163.24927 -2.847792821 -570.0935313 -172.4850546 172.4850546
    Freq:1.27 851.45184 -150.89906 -2.632350269 -743.4146135 -415.096312 415.096312
    Freq:1.00 1176.3042 -140.24664 -2.44652472 -903.4136196 -753.349456 753.349456

    The Nyquist plot for the above table 

      

    The Expected Nyquist Plot (Obtained from electrochemical Workstation)

  • Hi,

    The swing may be due to saturation.

    You may do two measurements:

    1) One with HSTIARTIA_200


     2) Another with HSTIARTIA_40K

    and check if you get expected readings with any one.

  • Hi Akila,
    The above settings didn't work for me.
    I decided to measure impedance magnitude and phase values of a resistor and capacitor in parallel.
    Impedance magnitude value matched with theoretical value but phase values did not match.

    Top View of RC Parallel connection

    Default settings
    Resistor Value Capacitor Value Frequency Impedance Phase Expected Impedance Expected Phase Amplitude RTIA RCal
    1kOhms 1 uF 1 Hz 5995.945 Ohms 0.251 rad 999.98026 Ω -0.00628 rad 600 mVpp 200 Ohms 10000 Ohms
    1kOhms 1 uF 10 Hz 2752.376 Ohms 1.076 rad 998.0319 Ω -1.41297 rad 600 mVpp 200 Ohms 10000 Ohms
    1 kOhms 1 uF 50 Hz 1023.359 Ohms -18.533 rad 954.02822 Ω -0.3044 rad 600 mVpp 200 Ohms 10000 Ohms
    1kOhms 1 uF 100 Hz 886.897 Ohms -30.295 rad 846.73302 Ω -0.56098 rad 600 mVpp 200 Ohms 10000 Ohms
    1kOhms 1 uF 150 Hz 754.394 Ohms -38.597 rad 727.72718 Ω -0.75579 rad 600 mVpp 200 Ohms 10000 Ohms
    1kOhms 1 uF 500 Hz 336.016 Ohms -51.988 rad 303.31447 Ω -1.26263 rad 600 mVpp 200 Ohms 10000 Ohms
    1kOhms 1 uF 1000 Hz 204.849 Ohms -45.288 rad 157.17673 Ω -1.41297 rad 600 mVpp 200 Ohms 10000 Ohms
    1kOhms 1 uF 10000 Hz 117.289 Ohms -7.583 rad 15.91348 Ω -1.55488 rad 600 mVpp 200 Ohms

    10000 Ohms

    The above measurements were done in SensorPal 

    Could you tell me how to get phase values correct ?