Confusing Amplitude Levels: Scope vs. Spectrum Mode

Post any questions you may have about our current range of oscilloscopes
Post Reply
risto
Newbie
Posts: 0
Joined: Tue Jun 11, 2013 7:18 am

Confusing Amplitude Levels: Scope vs. Spectrum Mode

Post by risto »

Hi there,

I'm using the PicoScope 4262.
When applying a 2 Volt DC Signal in scope mode I see a correct horizontal line at about 2 Volts.
But in Spectrum Mode (0 to 100Hz , linear,blackman, N=2048) at about zero Hz a peak with approx 4 Volts is measured.
Why is the Amplitude in spectrum mode two times higher than in scope mode?

Another case:
Applying a 1kHz sinewave with 1Volt amplitude from the picoscope AWG generator to Port A:
- In scope mode a Sinewave with 1 Volt Amplitude can be seen.
- In spectrum mode (0 to 2000Hz , linear,blackman) at about 1 kHz a peak with approx 0.7 Volts is measured.
Why is the Amplitude in spectrum mode lower than in scope mode?

Risto

Hitesh

Re: Confusing Amplitude Levels: Scope vs. Spectrum Mode

Post by Hitesh »

Hi Risto,

The 4V is an anomaly as an FFT isn't meant to be applied on the zero frequency component.

The amplitude for the 1V sine wave is lower is because it is a Root Mean Square (RMS) calculation.

I hope this helps.

Post Reply