WaveForms Measurements Are All Wrong When Attenuation is Changed

[Jay P.]

WaveForms' Measurements are all wrong when Attenuation is changed from 1X. Thus, in the attached screenshot, changing the Attenuation to 100 uX should have automatically scaled the Amplitude and Peak2Peak up by a factor of 10,000. This is not the case: the Amplitude should be around 167 uV, and Peak2Peak twice that number (is that twice? No, it's 10 times the Amplitude!).

[attila]

Hi @Jay P.

See the following:

[Jay P.]

attila, thank you, but my question was about the scaling, not Peak2Peak.

[attila]

Hi @Jay P.

The changing the attenuation does not scale the existing capture, but it will be applied on the following captures.

[Jay P.]

attila, this is not a capture, this is a free-running signal, and even an hour later the measurements are still incorrect. You guys clearly have a problem here: the measurements must be scaled accordingly with the Attenuation. Please, instruct clearly what needs to be done to scale the measurements by the same factor as the Attenuation.

Edited April 27, 2023 by Jay P.

[attila]

Hi @Jay P.

I don't see any problem here. The scaling seems to me correct.

The peak2peak is the distance between maximum and minimum.
The amplitude is half of the high and low distance. The low/high are determined from peaks of the histogram. 

Here you can see two captures, first with 1X and the second with 1/10000X.
Y1/2 are the min/max and Y3/4 low/high
The vertical scaling in the plot and measurements values look good to me.

In your capture the amplitude is ~16nV = (152nV - 120nV)/2

[Jay P.]

You problem is right here staring at you: your signal appears 10,000 smaller because you changed the Attenuation:

[attila]

Hi @Jay P.

Attenuation above 1X (absolute) means the input signal the scope receives are attenuated. If a 30V signal is passed through 10X attenuation the scope will read 3V. Specifying this 10X option for the software this will multiply the reading by 10, represent the read 3V as 30V in the plot, in measurements, in trigger level...
Attenuations below 1X (absolute) mean amplification. For instance 0.01X means the original signal is 100 times amplified for the scope input, so for representation it is divided by 100 to show the original levels before the amplification.
This option can also be used to represent current, when voltage drop on a shunt resistor is measured.
You can also use negative attenuation value to invert the signal.

[Jay P.]

attila, thank you very much, but my signal is not amplified nor attenuated. Isn't there a way to display its correct Amplitude and Peak2Peak when Attenuation is changed???

You are probably thinking about a probe with attenuation, and Attenuation in Waveforms is compensating for it, but I'm not using a probe — I am simply passing a low-voltage signal and I need its Amplitude to display correctly.

[attila]

Hi @Jay P.

If your signal is not amplified or attenuated then leave it at (specify) 1X
The attenuation option does not modify the existing capture.
You could eventually Add and use a Math channel like this:

[Jay P.]

I cannot leave it at !X because the signal is too small for 1X and it's buried in noise. I can only see the signal when I lower the Attenuation. The noise floor is too high for 1X  it is around –40 dBV.

[attila]

Hi @Jay P.

You can reduce the channel Range and Bottom in the FFT view...

[Jay P.]

Unfortunately, reducing the channel Range and Bottom in the FFT view wоuld not change the Amplitude and Peak2Peak in the Oscilloscope view. ☹️

Edited May 6, 2023 by Jay P.

[attila]

Hi @Jay P.

If you want to artificially amplify the signal use attenuation above 1X
Like here a 10mV amplitude signal, captured specifying 10000X it is represented as 100V signal.