CN0510 calibration reporting integers

Hi,

Could you check with Sensorpal GUI as it has default AFE parameters ideal for battery measurement.

By calibration output, do you mean the RcalVolt values displayed in the beginning as below:

Rcalvolt gives Vrcal = current through Rcal X RTIA

where,

RTIA = feedback resistor of HSTIA 

Vrcal is shown in Cartesian format.

It is not clear what you meant by Vcal and Vexcite.

I shifted over to the embedded approach because we werent getting anything that looked reasonable from sensorpal

Here's a result  I took just now using sensorpal on the same battery.  While not as messy, it still seems like nonsense.  Except for the first frequency measurement, the values all say -500milliohm.

https://imgur.com/a/XovrRvM

this battery has an open circuit voltage of 4.8V.  According to SensorPal, the DC bias cannot be set above 1200mV.  What is the DC bias referring to?

------------------------

For the calibration , yes, those numbers are what I was referring to.  Based on the description I read in the manual, I had the impression that it was doing some form of voltammetry.

Can you send some kind of paper describing the maths behind the HSTIA calculation and polar coordinates you mention?

I thought it was referring to the 50mohm calibration

here's  the actual data so you can plot it yourself

Real (mΩ)    Imaginary
538.177002    94.26971436
-551.1313477    18.80330658
-549.8725586    19.28751564
-549.0904541    19.90185738
-552.3719482    17.58491516
-549.7922363    19.6134491
-548.6862793    19.51558685
-548.0761719    21.19915962
-548.953125    22.80607986
-549.5705566    20.9835453
-550.6514893    21.51584053
-546.7858887    21.42605591
-546.2318115    21.18035507
-545.5237427    19.87710953
-544.8445435    20.41915894
-547.9258423    23.139534
-545.9963379    21.99766731
-543.2149048    20.19886971
-543.0961914    21.25439835
-558.9587402    16.2287159

Hi,

How are you saying that this is nonsense value? Do you have any expected impedance value? any reference plot for your battery load?

There is no mention of voltammetry in battery impedance manual.

DC bias has nothing to do with battery voltage. It is a control voltage to control the current flow through battery and circuit around it.

Purpose of TIA in general is to convert input current into voltage and output this voltage to the next block.

Maths behind TIA current to voltage conversion is available in general google search or wikipedia.

For this board, it is 

Vrcal = current through Rcal X RTIA

Vbat = current through Battery X RTIA

Battery impedance = Zbat = Vbat/Vrcal * Rcal         //mentioned as comment in code itself

Below is an example of battery impedances obtained using sensorpal:

NCR18650A Battery:

AA Battery:

Measurement of another AA battery using code in Github:

No expected model yet. These were the first batteries we've tried and they are just generic NiMH.  So I take your point and I will cut one pack up and measure some single cells to simplify the result.

I say nonsense because:

  1. the results are not repeating from run to run

  2. they are not showing any directionality, the nyquist plot jumps erratically in any direction from one frequency to the next.  While there certainly is variability in shape, each of your test plots show some kind of trend.  I am not currently getting that.

But i'll need to wait till tomorrow to show multiple tests on sensor pal at 1200mV bias.

Akila said:

DC bias has nothing to do with battery voltage. It is a control voltage to control the current flow through battery and circuit around it.

Sounds like I should just stick to the default 1200mV then.  Is there any situation under in a different bias setting is preferred?

----------------------

Re: the calibration

I guess voltammetry is the wrong word, my comment was from the part about measuring voltage drop in the measuring voltage section on page 4 here:

https://www.analog.com/media/en/reference-design-documentation/reference-designs/CN0510.pdf

I did some reading on TIAs earlier for the first time.  When you say:

Akila said:

Purpose of TIA in general is to convert input current into voltage and output this voltage to the next block.

Does block refer to discrete time interval?  My understanding is that the TIA feeds into the ADC.  I see the equations.  I don't understand where polar co-ordinates come into play when measuring a passive resistor.  The calibration resistor is non-reactive right?

Akila said:

Vrcal = current through Rcal X RTIA

The calibration values in your screenshot are quite different from what I posted above.  I can imagine that there are several variables that might differ between my test environment and yours. The battery is out of the circuit during calibration though so I would expect the differences to be relatively small.

Is there some intuition I can form (or pattern I can look for) in the calibration data to satisfy myself that the board is taking good, stable measurements? Or should I just ignore the calibration being reported?

Thank you for the assistance

No expected model yet. These were the first batteries we've tried and they are just generic NiMH.  So I take your point and I will cut one pack up and measure some single cells to simplify the result.

I say nonsense because:

  1. the results are not repeating from run to run

  2. they are not showing any directionality, the nyquist plot jumps erratically in any direction from one frequency to the next.  While there certainly is variability in shape, each of your test plots show some kind of trend.  I am not currently getting that.

But i'll need to wait till tomorrow to show multiple tests on sensor pal at 1200mV bias.

Akila said:

DC bias has nothing to do with battery voltage. It is a control voltage to control the current flow through battery and circuit around it.

Sounds like I should just stick to the default 1200mV then.  Is there any situation under in a different bias setting is preferred?

----------------------

Re: the calibration

I guess voltammetry is the wrong word, my comment was from the part about measuring voltage drop in the measuring voltage section on page 4 here:

https://www.analog.com/media/en/reference-design-documentation/reference-designs/CN0510.pdf

I did some reading on TIAs earlier for the first time.  When you say:

Akila said:

Purpose of TIA in general is to convert input current into voltage and output this voltage to the next block.

Does block refer to discrete time interval?  My understanding is that the TIA feeds into the ADC.  I see the equations.  I don't understand where polar co-ordinates come into play when measuring a passive resistor.  The calibration resistor is non-reactive right?

Akila said:

Vrcal = current through Rcal X RTIA

The calibration values in your screenshot are quite different from what I posted above.  I can imagine that there are several variables that might differ between my test environment and yours. The battery is out of the circuit during calibration though so I would expect the differences to be relatively small.

Is there some intuition I can form (or pattern I can look for) in the calibration data to satisfy myself that the board is taking good, stable measurements? Or should I just ignore the calibration being reported?

Thank you for the assistance