DC voltage is useful for measuring phenomena that change slowly with time?

[Twoward]

I read the following in the help file:
DC voltage is useful for measuring phenomena that change slowly with time, such as temperature, pressure, or strain. With DC signals, you want to accurately measure the amplitude of a signal at a given point in time.

My eyetracker outputs fast changing voltages. (grounded signal 0-5V)
Could anybody please explain to me how I should read these values, or better: How should I read that comment in the help file?

[Twoward]

As far as I know I get correct readdings through voltage, connected to ground, acquisition.
But why was that remark made in the help file?

[Ed W]

Hi Twoward,

It sounds like you are measuring a DC voltage.  While it may vary with time, it is not truly an AC signal.  An AC signal implies that it is represented as a sinusoid.

The main thing to remember when measuring DC signals is that you have to sample at least twice as high as the highest frequency component that you want to analyze.  So if the highest frequency component of your signal is 100Hz, make sure to sample at least 200 times per second.

I hope this helps!

Ed W.

[Twoward]

Hello Ed W,

Okay, there is a difference in the concept of 'slow' 😄
The signal surely isn't an alternating one. Its just the rotation of the eye translated into voltages.(Although these changes can be unexpectedly fast).
Most eyetrackers measure at 500Hz, at most. This is mostly because their (lack of)accuracy makes higher frequency measurements a wast of processing power.
Concluding: I think my setup is correct.

Thanks!