Programming instructions

National Instruments Corporation 5-1 LabVIEW Data Acquisition Basics Manual

Things You Should Know

about Analog Input

Hunting has been a part of survival from the beginning of time. People

used to hunt for the things they needed to survive, like food and water.

Today, engineers and scientists use data acquisition to “hunt down” the

information they need to survive in the information age. This chapter

focuses on defining the tools you need to be a successful hunter in the

world of data acquisition.

Defining Your Signal

You and your friends plan a hunting trip for this weekend. What do you

plan to bring with you? This question is really not valid, because you must

know first

what

you will be hunting before you pack your fishing pole or

elephant rifle. The same idea applies to scientists and engineers engaged

in the quest for information. You must know the defining characteristics

of what you want to “hunt,” be it a wild animal or an analog signal.

You cannot just say, “I will hunt voltages,” or even “I will hunt analog

voltages.” Voltages come in various forms. This chapter gives you the

terms, tools, and techniques designed to help show you the best way to

catch your wave.

You can break down analog signals into three categories: DC, time domain,

and frequency domain. You must ask yourself, “Is the information I seek

primarily contained in the level, the shape, or the frequency content of my

signal?” Figure 5-1 illustrates which signals correspond to certain types of

signal information.

Figure 5-1.

Types of Analog Signals

Analog Signal

Time Domain

Frequency Domain

ADC/DAC

(slow)

ADC/DAC

(fast)

ADC (fast)

Analysis

Level

Shape

Freq. Content

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