Programming instructions

© National Instruments Corporation 7-1 LabVIEW Data Acquisition Basics Manual
7
Buffering Your Way through
Waveform Acquisition
If you want to take more than one reading on one or more channels, there
are two techniques you can use depending on what you want to do with the
data after you acquire it. This chapter reviews these different methods and
explains how LabVIEW stores the acquired data with each method. You
will discover which method you should use by answering the following
questions.
• Do you want to analyze your data as it is being acquired or after it has
been acquired?
• Do you want to acquire a predetermined or indefinite number of data
points?
If you want to analyze your data as it is being measured and the number of
data points does not matter, read the
Do You Need To Access Your Data
during Acquisition?
section in this chapter. If you acquire a predetermined
number of data points and you want to analyze the data after it has been
acquired, refer to the
Can You Wait for Your Data?
section in this chapter.
Also, throughout the chapter there are some basic examples of some
common data acquisition (DAQ) applications that use these two methods.
Can You Wait for Your Data?
One way to acquire multiple data points for one or more channels is to use
the non-buffered methods described in the previous chapter in a repetitive
manner. For example, you could compare this method to a trip to the
grocery store. You need to get 20 items from the store, but because you
can’t carry all 20 items at once, you decide you must make 20 separate trips
to the store. Grocery shopping in this manner would be very inefficient and
time consuming. The same applies for when you are acquiring a single data
point from one or more channels over and over. Also, with this method of
acquisition, you do not have accurate control over the time between each
sample or channel. Going back to the example of grocery shopping, it
would be much more efficient to use a shopping bag to hold all 20 food
items at once, so that you only have to make one trip. In the same sense,