how do update rate relate to frequency of a waveform, and how do i store a waveform in the buffer?

[JrodMillar]

I am confused on how update rate affects the frequency of an actual signal in labview? Can someone explain this?

[Ben]

THe update rate talks about how often a new value is read/written.

The pattern of these update values represent/control the frequency of the signal.

Say, you are watching a very boring TV show called "1&2".

This show features a big "1" on the screen or a big "2". Durring the show, the screen switches back and forth between either showing you the "1" or the "2".

Let say the switching back and forth between "1" and "2" occurs once every 5 seconds.

The whole time you have been watching the show, the TV screen is being re-painted about 60 times a second.

In this scenario the "update rate" is 60 times a second, or 60 Hz. The frequency of the "signal" is once every 5 seconds or 0.2 Hz.

Does this get you somewhere?

Ben

[Randy_H]

Ben,

I think this is a great answer to that question.

Randy Hoskin
Applications Engineer
National Instruments
http://www.ni.com/ask

[Ben]

Thank you Randy.

Ben

[DougD]

JrodMillar:

You must take samples at least twice as fast as the highest frequency
that you are interested in analyzing and which physically occur in the
phenomena you are analyzing. This is an old but very important rule
of signal sampling referred to as the Nyquist Theorem for it's
original discoverer.

Consider what is the limiting factor - the signal of interest (i.e.
the physical phenomena), the responsiveness of your sensors to that
signal, or some other cut off frequency criteria (e.g. do you care
about the 5th harmonics of the signal or is the power distributed in
them too low to care about?)

If you do not do this then you will "alias" the signal or i.e. miss
relevant signal data from your scan and possibly draw wrong
conclusions from the data.


Do
uglas De Clue
LabVIEW developer
ddeclue@bellsouth.net

JrodMillar wrote in message news:<506500000008000000E8510000-1023576873000@exchange.ni.com>...
> I am confused on how update rate affects the frequency of an actual
> signal in labview? Can someone explain this?