Why does the amplitude at low frequencies drops in the Analog Discovery 2?

[Camarillo]

Hello.

 

First some context:

I´m doing a measurement of a signal that has a 10 second period. It is comprised of several 100 us signals, all in that period. Such signal has a maximum 50 mV amplitude.

 

This might be a very basic question but I´ll ask it anyway:

If I zoom in to the 100us signal, I can see the correct amplitude.

If I zoom out such as to capture the 10 second period, the amplitude decreases drastically (about 75% of the original value).

 

Is there something that I´m doing wrong?

 

 

Thanks in advance.

[attila]

Hi @Camarillo

With Repeated mode when changing the time Base the sample Rate is also adjusted. The default Sample Mode for the Channels is Average.
You could use Record mode for up to 1-2MHz or Min/Max sampling.

[Camarillo]

Thanks @attila, will test this later at the lab.

 

If I want to record the signal for 5 minutes, should I use the record option or the log option?    I´m doing measurements with Labview and will incorporate the AD2 to measure this signal.

 

Will post the result later this day.

 

Thanks again.

[Camarillo]

Hi, just got back from the lab and I think i don´t understand this that well......

 

This is the actual 100uS signal that I want to measure. Please note that the amplitude is 20 mV/div.

The signal should be around 55 or 57 mV.

The frequency of such signal is 25 Hz (with a pulse width of 100uS).

 

 

This is a closer look at the signal.

Please note the change in the peak values. The normal signal hovers around 60 mV, and now the AD2 shows peaks of 100 mV. Still, the width is still around 100uS and the plateau is near that 60 mV value.

 

If I try to measure the signal for a longer time, the voltage is not what is suppose to be. Please note the value drop to about 10 mV instead of the 60 mV.

This is the same 100uS width at around 60 mV pulse as the first image.

 

 

 

The actual signal that I want to measure is 10 seconds long (looks like the next one). Since I want to incorporate the AD2 in LabVIEW with another sensor, I first want to know if the AD2 can measure the actual voltaje. 

 

Maybe my measuring skills are wrong and I need to go back to school.

 

Can you provide some insight @attilain this regard?

 

Thanks a lot.

 

 

 

PS:

I found this post but still can´t get the grasp on the concept:

 

Edited May 4, 2022 by Camarillo

[attila]

Hi @Camarillo

In your last capture the 100us pulses sampled at 625us (1.6kHz), with the default average mode, will represent at most 16% (100/625) of the sample value.