Average/Averaging

[Bushara]

I would like to know  in practice what is the difference between those parameters (Average/Averaging) and what they do. Also, what is the function of the parameter Samples?

 

Edited July 26, 2022 by Bushara

[JColvin]

Hi @Bushara,

Which Digilent product are you referring to so I can help make sure you get an answer appropriate to your question?

Thanks,
JColvin

[Bushara]

Hi @JColvin,

 

Here I attached the model I am asking about. I use the Analog Discovery 2 for impedance measurement, with the impedance analyzer attached to the Analog Discovery.

 

Thanks,

Bushara

Edited July 26, 2022 by Bushara

[mgatsharelatex]

Great question! 

I have also found it very difficult to find detailed explanations/documentations about what these kind of user defined parameters actually mean, and therefore also how they differ from each other. Perhaps there is some additional manual and/or examples available that I have yet not discovered?

I think the Analog Discovery 2 is really really nice, but in order to be able to use it properly for my intended applications, I have to truly understand what these parameters are.

Best wishes,

Mats

[JColvin]

Hi @Bushara and @mgatsharelatex,

I have moved this thread to a more appropriate section of the Forum. Much of the documentation can be found in the Help tab of WaveForms and selecting the Browse option which brings up the built-in WaveForms documentation. The Averaging, Average, and Samples are then all defined in the Control subsection of Impedance (screenshot attached below of the screen you would be looking at).

To more directly answer your questions (as I understand them):

Averaging - this will specify the amount of time taken for each step
Average - This is the number of captures to average in each step and will show at least the number of average captures (or more if it can manage to capture more samples during the Averaging time.
Note: as per these two Forum threads (https://forum.digilent.com/topic/19370-ad2-accuracy-of-impedance-analyzer/ and https://forum.digilent.com/topic/19158-analog-discovery-2-impedance-analyzer-questions/) the two conditions have AND logic so both conditions will be satisfied during each step.

Samples - The number of samples to capture in each step (with the default being the maximum value which changes depending on the Analog Input buffer size Analog Discovery 2 configuration selected in the WaveForms Device Manager).

Let me know if you have any questions about this.

Thanks,
JColvin

[mgatsharelatex]

Many thanks @JColvin for this valuable information. I have now been in contact with Bushara to confirm that he/we still do not fully understand. Moreover,  it seems you are also not fully certain (as you write "as i understand them")? We already knew about the documentation that you are referring to, the problem is that the descriptions there are too short and non-specificto be fully understandable, for example:

(1) "Averaging - this will specify the amount of time taken for each step".  Does this mean that a more descriptive name would  "Averaging time interval length"? Moreover, the word "step" is not defined. I guess "step" actually mean "frequency step" here? 

(2) "Average - This is the number of captures to average in each step and will show at least the number of average captures (or more if it can manage to capture more samples during the Averaging time." Again here there are undefined words like "captures". What is the difference between "number of captures”  and "number of samples to to capture” . What happens if the Averaging  (=Averaging time ) is too short compared to the selected Average=number of
captures. For example: Assume we choose Average=100000 and Averaging 1 microsecond. Then the instrument will not
be able to collect anything because the required sampling frequency will be too high.

(3) "Samples - The number of samples to capture in each step (with the default being the maximum value which changes depending on the Analog Input buffer size Analog Discovery 2 configuration selected in the WaveForms Device Manager)." This is a very unclear as it does not explain HOW the changes are
dependent on the selection of the input buffer size. It is also unclear what is the "buffer size" in this context so more details are needed.

 

In other words: We are in need of much more detailed definitions and/or explanations of words like "step", "caption","  sample", "input buffer," "input buffer size".  Moreover we are hoping for explanations and/or manuals that can explain all user defined parameters in detail, their intended role, and some recommendations/motivations for how the values of them should be chosen.

Many thanks again!

 

Best wishes,

 

Mats

 

 

[JColvin]

Hi @mgatsharelatex and @Bushara,

Ok, I think I understand your confusion with the variables better now. Reviewing the documentation further, I realize that I also used some general terminology associated with oscilloscopes/analog inputs interchangeably with some of the defined parameters of the Impedance Analyzer tool within the WaveForms software, so I apologize for being part of the confusion on that end.

Lets see if I can help make some things more clear (though I will still be using the definitions mentioned in the document I linked, just with a bit more explanation):

Samples:
In WaveForms in general as well as within the Impedance Analyzer tool, a "Sample" is a single piece of data that was measured by the analog-to-digital converter of  whichever Digilent Test and Measurement product you happen to be using. In the Impedance tool, the Samples variable in the Options dropdown lets you choose number of single point measurements that you want the ADC to take to compare the measured sine wave applied both before and after the DUT to see how its phase and amplitude have shifted. The maximum is dictated by the buffer size of the Test and Measurement device in question; for the Analog Discovery 2 in its default configuration, this is 8000 measurements at 14-bit resolution. A higher number of samples improves the accuracy of the measured sine wave, but can slow down the measurement process at large since inherently more math will need to be done in the impedance calculations.

Captures:
A "Capture" is one full set of ADC samples taken at a particular frequency step. The options dropdown menu in the Impedance Tool also lets you specify some other conditions related to the capture, specifically the "Min Periods" which dictates the minimum number full periods of the generated sine wave you want to measure in a single capture. The minimum qualification is important here because if your starting frequency value for your Impedance Analyzer sweep is very low and you are wanting to get a certain number of sine wave periods (and perhaps average a certain number of captures which I'll define in a bit), the Impedance Tool may take a longer amount of time to get all of the necessary measurements by pure virtue of the sine wave simply being at a slow enough frequency. As a quick example, if you want to average 100 captures (effectively sets of data) that consist of 16 periods of a 1 kHz sine wave, that will take 1 ms/period * 16 periods * 100 data sets = 1600 ms of measurement time per frequency step.

Average:
This dropdown parameter in the Options menu lets you choose the minimum number of captures (again, where each capture consists of a set number of sample points that span some number of sine wave periods) to take at each frequency step. Key takeaway here is that this is a minimum number of captures that will have their measurements averaged.

Averaging:
This parameter is like you presumed; the minimum amount of time the ADC will be taking measurements at each frequency step.

Since the "Average" and "Averaging" parameters are both minimum values, the WaveForms software using AND logic to ensure both minimum requirements are met. So, like in your example of setting the Average parameter to 100000 (average one hundred thousand data captures of some number of sine wave periods) and an Averaging time of 1 microsecond, the Digilent Test and Measurement device (Analog Discovery 2 or whatever you happen to be using the Impedance Tool on) will not progress to the next frequency step until all 100000 captures have been measured. The inverse of using an Average of 2 captures but a sampling time of 500 milliseconds will also not let the device progress to the next frequency step until the 500 milliseconds of measurement time has been reached.
In that second/inverse example, since the system has extra time, it will measure as many captures as it can to average rather than limiting itself to the 2 captures.

Input Buffer/Input Buffer Size:
This is the amount of measurements (samples) that a particular Test and Measurement device can measure in a single capture. This is a size limit imposed by the FPGA hardware, though WaveForms offers different configuration options (available in the WaveForms Device Manager where you select what Test and Measurement device you want to connect to) that will let you choose which buffer size to allocate to different parts of the Test and Measurement hardware (analog inputs, analog outputs, digital IO).

Amplification:
A setting to let the WaveForms software know if you are externally amplifying the sine wave this is being produced by the WaveForm generator, so that way the WaveForms software does not misinterpret and calculate incorrect results when it compares the measured sine wave before/after the DUT to the sine wave it thinks it provided.

ProbeRes and ProbeCap:
Settings you can choose to specify probe resistance and capacitance in case you are external probes and directly using the Digilent Test and Measurement device.

Settle:
An amount of time that the Test and Measurement device will wait after going to the next frequency step before starting to take ADC measurements.

Please let me know if you have any questions about this or other parameters or if my explanation is unclear.

Thank you,
JColvin

P.S. @attila please correct me if any of my explanations are wrong or incomplete