Impedance Analyzer adapter: why the constant voltage mode turn the resistor alarm on?

[EzeStare]

The impedance Analyzer description said  “The Impedance Analyzer for Analog Discovery provides automatically adjusting reference resistors and relays, so that reference circuits don't have to be manually built for each test. “

When we used the IA and "constant voltage" mode, the alarms turn on more than we have expected

Here, we show the impedance behavior of the same DUT (RC circuit), using the constant voltage mode (10 mV), with or without the impedance Analyzer adapter, alternatively.

When we used the W1-C1-DUT-C2-R2-GND configuration (without the adapter) with external 4,7kOhm reference resistor, the resistor alarm was turn off for all the frequency range. While, when we used the adapter (with six internal reference resistors), the “resistor too High” alarm turned on in almost all the frequency range.

why the constant voltage mode turn the resistor alarm on? 

How can we solve the resistor alarm using adapter and constant voltage mode?

WITHOUT Impedance Analyzer adapter using the W1-C1-DUT-C2-R2-GND configuration. The external reference resistor was

 

WITH  Impedance Analyzer adapter

Edited August 23, 2021 by EzeStare

[attila]

Hi @EzeStare

The Constant Voltage/Current works differently with and w/o Adapter.
With Adapter automatically changes the reference resistor, for your experiment it set it to 1M.

Use the Custom mode and load the Constant Voltage example, specify the rms voltage in the script, "const Voltage = ..."

[EzeStare]

Oh! Forgot to add those.

First try

Same RC circuit as before

Same Randles circuit as before

 

Second Try

Same RC circuit as before

Same Randles circuit as before

 

[............]

There are more, but these should be enought. 

The point is: if the Impedance Analyzer is suposed to give a better EIS experience, then why its worst than without the IA?

I mean, the alarms are not the only thing. Even in the post processed data Error values tends to be bigger with IA than without it. Sometimes this difference this absurdly bigger.

 

Edited August 26, 2021 by EzeStare

[attila]

Hi @EzeStare

As I told earlier, the CC/CV with adapter also changes the resistor automatically. In some cases this is an advantage but not in your experiment.
For the next software version I will add CC/CV options for adapter without resistor change.
Until this, please use the earlier mentioned Custom script:

 

[EzeStare]

First of all. Thank @attila you for yout prompt responses. Both times.

And of course, hi.

About the usage of a Custom script or another. I used "Constat Voltage Adapter" assuming that if I connet the Impedance Analyser this onse should be the correct.

1-Are you saying that even if I connect the Impedance Analyzer I should hace used the Custom Script "Constat Voltage"?

 

 

Well, even I used the wrong Custom Script it could help me to ask you some doubts.

So ... if I understar correctly you are saying that with the script I can't control how the Impedance Analyzer select the resistance. Right?
therefore, if I use this code as an example:

2-Is this code the exactly one that makes de option "constat voltage" works? (when IA is connected)

Secondly, if I change:

   3-Resistor: Am I just changing the value of the measured resistance? (Measured by the c2). And this measured resistance is the one measured with the c2. Right?

   4-If i undertood correctly the previous point: like the Resistor variable, are modification applied to Amplitude just a modification on a measured value? (by c2)

   5-Voltage is the desired VRMS. But what about VRMS variable? where is it declared and defined?

   6-Finally, what is the Repeat varible used for?

 

Edited August 29, 2021 by EzeStare

[attila]

Hi @EzeStare

1. Yes. Use the Custom mode and "Constant Voltage" example with Adapter to prevent resistor changing. This will be similar to Constant Voltage mode without Adapter.
(Or choose Adapter, select the required Resistor and choose "W1-C1-DUT..." to prevent resistor changing during CV/CA mode run.)

2. The "Constant Voltage Adapter" example is similar to the "Constant Voltage" mode with Adapter. The code is given to be able to customize or finetune the adjustment process if needed.

3.4. Resistor variable is the reference resistor value.
The Scope C2 measures the voltage on this Resistor thus giving the current.

5. The VRMS variable is the measured Vrms. The Voltage is a constant in the code.

6. The Repeat variable is used to repeat the step measurement, like to have some settle time after the Resistor is changed, to ignore the transients.

See all the variables in the editor under insert:

[EzeStare]

Many, MANY thanks. You have solved many doubts I had. 

It's not the same just to thinks it is that way than to be instructed. 

Let me ask you some more about the things that I already asked and a little more.

1- I understood that if I use the Custom Mode and "constant voltage" example with the Impedace Analyzer the resistor will NOT change automatically. But, it means that if I use "Constat Voltage Adapter" intead, the Impedance Analyzer will change the reference resistor automatically. Right?

So, if I use something like (just to say something)

if(Amplitud==10000) {Resistor=10000}

 the Impedance Analyser will set the reference resistor at 10 kOhm if an Amplitude equal to 10000 is detected. 

2-Is my interpretation correct?

14 hours ago, attila said:

The Scope C2 measures the voltage on this Resistor thus giving the current.

5. The VRMS variable is the measured Vrms. The Voltage is a constant in the code.

4-About this: How is the "VRMS" value measured? Is it the voltage value on C2 or it is the calculated C1-C2 difference value? 

5-If I understood correctly the "Aplitude" variable is just a value calculated from "Voltage" and "VRMS". It is defined "Amplitude=0"  before the EIS start (so the first "if" is executed)?

 

Edited August 31, 2021 by EzeStare

[EzeStare]

And now... Something less conceptual.

We need to fix 10mV between the DUT in all the samples along the frequency range we measure (1Hz to 1MHz).  
Then our DUT may change the impedance a lot along the frequency range and so we need to adjust both amplitude and the resistor (that's why we are trying so hard with the Impedance Analyzer).

I will try this:

const Voltage = 0.01 // desired VRMS
const MaxAmplitude = 2.5 // maximum AWG amplitude   
/*#######  Is this still available "The AWG output range (Offset + - Amplitude) of Analog Discovery 1 & 2 is guaranteed between -5V and +5V"?
from: https://forum.digilentinc.com/topic/2364-squarewave-amplitude-error/?do=findComment&comment=8122*/

if(Amplitude==0) { // first step, initialize 
    Resistor = 1e5        /*chanched 1e6 for 1e5*/
    Amplitude = Voltage*Math.SQRT2
    Repeat = 2 // repeat step twice
}
else{ // adjust amplitude based on VRMS
    Amplitude *= Voltage/VRMS
    if(Frecuency==10){
        Resistor = 5e4
        Repeat = 2 // repeat step twice
    }if(Frecuency==50){ 
        Resistor = 1e4
        Repeat = 2 // repeat step twice
    }if(Frecuency==500){ 
        Resistor = 1e3
        Repeat = 2 // repeat step twice
                    
    }else if(Repeat){
        Repeat--
    }else{
        Repeat = 1 // do each step twice, to adjust and measure
    }
}

For this excercise:

On 8/26/2021 at 12:32 PM, EzeStare said:

it as before

Can you say me if you look this legitimate?

 

Edited August 31, 2021 by EzeStare

[attila]

Hi @EzeStare

Use Custom "Constant Voltage" with 1k or 10k
At such low voltages you may want to use some Averaging (or Options/Average) to have a cleaner capture.