Chapter 10 Things You Should Know about Analog Output. NI LabVIEW Data Acquisition Basics

Things You Should Know about Analog Output

Some measuring systems require that analog signals be generated by a

DAQ device. Each of these analog signals can be a steady or slowly changing signal, or a continuously changing waveform. This chapter describes how to use LabVIEW to produce all of these different types of signals.

Single-Point Output

When the signal level at the output is more important than the rate at which the output value changes, you need to generate a steady DC value. You can use the single-point analog output VIs to produce this type of output. With single-point analog output, any time you want to change the value on an analog output channel, you must call one of the VIs that produces a single update (a single value change). Therefore, you can change the output value only as fast as LabVIEW calls the VIs. This technique is called software

timing. You should use software timing if you do not need high-speed

generation or very accurate timing. Refer to Chapter 11, One-Stop

Single-Point Generation

, for more information on single-point output.

Buffered Analog Output

Sometimes in performing analog output, the rate that your updates occur is just as important as the signal level. This is called waveform generation, or

buffered analog output. For example, you might want your DAQ device to act as a function generator. You can do this by storing one cycle of sine wave data in an array and programming the DAQ device to generate the values continuously in the array one point at a time at a specified rate. This is known as single-buffered waveform generation. But what if you want to generate a continually changing waveform? For example, you might have a large file stored on disk that contains data you want to output. Because

LabVIEW cannot store the entire waveform in a single buffer, you must

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LabVIEW Data Acquisition Basics Manual

Chapter 10 Things You Should Know about Analog Output continually load new data into the buffer during the generation. This process requires the use of circular-buffered analog output in LabVIEW.

To learn more about single or circular buffering, read Chapter 12, Buffering

Your Way through Waveform Generation .

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