What are f0 and df when using "Constant Limit Testing"?

[flycast]

I am new to LabVIEW and NXG.

Using NXG.

I am trying to write tests for voltage signals. Just to learn I used "Constant Limit Testing (Frequency)".

There is no help available for f0 and df in the Context help on the Cluster properties. If I read the docs on Limit Testing I see the following:

spectrum

The input spectrum.

This input can be a cluster or an array of clusters.

f0

Start frequency, in Hz, of the spectrum.

Default: 0

df

Frequency resolution, in Hz, of the spectrum.

Default: 1

spectrum

Spectrum of the input signal.

Frequency makes sense to me when thinking about sound or vibration. In the case of a voltage measurement from a pressure sensor what would the start frequency and Hz be? These samples are taken every millisecond... so 1,000 hz for both f0 and df?

Here is a representative of what a typical pressure reading might look like (Blue line). In this case I might be interested in when the voltage goes over a set level like 4V or something:

[Bob_Schor]

I see you are using NXG, but I'm pretty sure my comments (which come from non-NXG LabVIEW) still apply.

When you deal with sampled signals, NI provides the Waveform data type that includes a Starting Time (t0), a sampling interval (dt), and an array of samples (Y) that start at time t0 and are acqured at times differing by dt.

When you go to analyze these sampled data, you might convert the time-series data into "Frequency space" by taking its spectrum, which takes N time points and returns to you N "frequency" components.  The same way that a Time Series has a Starting Time and a Time Interval, a Frequency Series has a Starting Frequency (f0) and a Frequency Interval (df).  For example, if I took 1000 points for 1 second at 1 kHz, I could describe this in "frequency-space" by reporting the components at 1, 2, 3, ... 500 Hz, so f0 = 1 Hz (the Starting Frequency) and df = 1 Hz (the frequency spacing).

Why stop at 500 Hz?  Go read a book on spectral theory, but be careful, it can get "complex" ...

Bob Schor