09-02-2013, 03:35 PM
Introduction to National Instruments LabVIEW 8 and
Data Acquisition
Introduction to National Instruments.pdf (Size: 437.82 KB / Downloads: 191)
Introduction
In this lab, you will create a LabVIEW virtual instrument (VI) to read data,
analyze it and display it to the screen. Through the use of virtual
instrumentation to acquire the voltages from a battery, you will learn how
measurement devices interface with both the computer and the physical world.
Objectives
Take data measurements using computer-based instrumentation
Become familiar with the LabVIEW and DAQ system environment
Understand the flow of data through acquiring, analyzing and presenting
LabVIEW
Creating LabVIEW systems begins with an understanding of PC-based data
acquisition. When data is collected from an instrument it passes through three
areas of interest. At the lowest level a sensor detects a physical phenomenon
and sends it back via a signal to the PC. There, a device known as a Data
Acquisition (DAQ) card takes the signal and converts it into digital data that
can be processed by the computer. After the data has been collected, steps
can be taken to make an analysis and a meaningful conclusion can be drawn.
LabVIEW provides the order and structure for these steps to occur.
The two parts to a LabVIEW VI are the front panel, a set of controls for the
user to manipulate while the system is running and the block diagram, a
collection of actions bound together like a flow-chart. The front panel can be
customized for any look and feel desired, while the block diagram can be
manipulated to clearly show the flow of data. When a LabVIEW system is
running, data is moved back and forth between the block diagram and the
front panel. It is important that the two be thought of together as a system
rather than running independently.
The front panel of a LabVIEW VI contains controls and indicators. As their
name suggests, controls are the inputs into the system, and the indicators are
the outputs. A simple example of what is possible with the front panel is
shown in Figure 1.
Spring ‘11 Lab 4 - Data Acquisition Lab 4-3
Example Front Panel.
In the above example there are six different buttons, five control buttons for
the radio and one “STOP” button which can be pressed with the mouse. To
begin, the user would click on the “Run” button . Then, when one of the
five radio buttons is pressed the number of the button appears in the Index of
Selection box, the indicator for the system. The LabVIEW system will run
continuously displaying the last button pressed until the STOP button is
pressed. Alternatively, there is a button shaped like a stop sign called the
Abort Execution button to the right of the Run button that can be used to
halt the system. It is always better to stop the program with the Stop button
on the front panel, however, instead of the Abort Execution button.
Buttons and numeric indicators are not the only things that can be placed on
the front panel. An assortment of graphical displays, lights, meters, sliders,
and other controls and indicators found on traditional instruments such as
function generators and oscilloscopes can be used on the VI front panel to
make the system interactive and easy to use.
The block diagram is where the user can link all of the parts of a LabVIEW
system together. Initially the user places the function icons that correspond to
the actions they wish the system to take on the block diagram. They are then
“wired” together in a set order to produce a coherent path through the system.
To illustrate the flow of a block diagram let us go through the following
diagram on the next page together.