Student’s Portion
Introduction
In this lab, you will learn about the basics of data acquisition. First, you
will configure your data acquisition hardware in Measurement &
Automation Explorer. Then, you will examine the data acquisition VIs in
LabVIEW. Finally, you will develop analog input applications.
Objective

Learn the three DAQ device grounding modes.

Learn the uses of Measurement & Automation Explorer.

Differentiate between single-point acquisition, continuous acquisition,
and buffered acquisition.
Theory
Measurement & Automation Explorer
Introduction
Measurement & Automation Explorer, or MAX, is a software interface
that gives you access to all National Instruments DAQ, GPIB, IMAQ, IVI,
Motion, VISA, and VXI devices connected to your system. The shortcut to
MAX is placed on the desktop during installation of NI-DAQ. MAX is
used primarily to configure and test National Instruments hardware, but it
offers other functionality, such as checking to see if you have the latest
version of NI-DAQ installed. The functionality of MAX is divided into
four categories:
• Data Neighborhood
• Devices and Interfaces
• Scales
• Software
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Data Neighborhood
Data Neighborhood contains the virtual channels. The Data Neighborhood
category shows you the currently configured virtual channels and provides
utilities for testing and reconfiguring those virtual channels. Data
Neighborhood also provides access to the DAQ Channel Wizard, which
allows you to create new virtual channels.
DAQ Channel Wizard
The DAQ Channel Wizard is a software interface that lets you create
new virtual channels. A virtual channel is a shortcut to a configured
channel in the system. You can set up the configuration information
for the channel and give the channel a descriptive name at the same
time. Later, you can use the descriptive name to access that channel
and its configuration information in LabVIEW. You can give the
channel a description, decide what type of transducer the channel will
use, set the range (determines gain), choose the grounding mode,
assign custom scaling for the virtual channel, and give the channel a
descriptive name to replace the channel number all at the same time.
For example, channel 0 on the BNC-2120 is hardwired to a
temperature sensor, so you could create a virtual channel for channel 0
and call it Temperature Sensor. You can create virtual channels for
analog input, analog output, and digital I/O. In this case, referring to a
channel by a name (Temperature Sensor) instead of a number (0) helps
you remember what the channel does.
Devices and Interfaces
Devices and Interfaces displays the currently installed and detected
National Instruments hardware. Devices and Interfaces also includes
utilities for configuring and testing devices. The two utilities that are
specific to DAQ devices are Properties and Test Panels.
Properties
Properties is a utility for configuring DAQ devices. When you launch
the Properties utility, a dialog box appears with the following tabs that
you can use to configure the DAQ devices.
• System—The System tab allows you to change the device number,
and it provides two buttons for testing the DAQ device. The first
button is the Test Resources button. After you have installed the DAQ
device, right-click Devices and Interfaces. Select Properties and
right-click Test Resources. This button performs a basic test of the
system resources assigned to the device. The system resources tested
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are the base I/O address, the interrupt request (IRQ), and the direct
memory access (DMA).
– Base I/O Address—A DAQ device communicates with a
computer primarily through its registers. NI-DAQ writes to
configuration registers on the device to configure the device, and
reads data registers on the device to obtain the device status or a
signal measurement. The base I/O address setting determines
where in the computer’s I/O space the device registers reside.
– Interrupt Request (IRQ)—Another way the DAQ device
communicates with the computer is through processor interrupts,
which give the processor the ability to respond quickly to its
peripherals. In the case of a DAQ device, it is not efficient for the
processor to continually check if data is ready to be read from the
device. A DAQ device can use an interrupt that signals the
processor that it has data waiting to be read. Each interrupt request
has a number assigned to it.
– Direct Memory Access (DMA)—The third way the DAQ
device can communicate with the computer is through direct
memory access (DMA). DMA is a data transfer method in which
data is transferred directly from the peripheral to computer
memory, bypassing the processor. DMA is usually required to
achieve maximum data transfer speed, making it useful for highspeed DAQ devices. DAQ devices that use the PCI bus have their
own onboard DMA channels, and the PCI bus handles the sharing
of that DMA.
• AI. The AI tab allows you to configure the default Polarity/Range for
the ADC and the default mode for grounding the DAQ device. The
default is applied only if the settings aren’t changed in LabVIEW.
• AO. The AO tab configures the default polarity of the analog output
signal, and allows you to specify if you are using an external voltage
reference for the DAC.
• Accessory. The Accessory tab specifies any accessories you are
using with the DAQ device such as the TBX-68 (terminal block with
built-in cold-junction compensation). If NI-DAQ does not need to
know about the accessory, it will not be on the list. In that case, choose
None.
• OPC. The OPC tab allows you to set the AI recalibration period if
you are using the NI-DAQ OPC server. The use of the NI-DAQ OPC
Server is beyond the scope of this lab.
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Test Panels
After the device passes the basic resource test and you configure the
System, AI, AO, Accessory, and OPC tabs, return to the System tab
and click the Test Panels button. The Test Panel is a utility for testing
the analog input, analog output, digital I/O, and counter functionality
of the DAQ device. The Test Panel is useful for troubleshooting
because it allows you to test the functionality of the device directly
from NI-DAQ. If the device does not work in the Test Panel, it will not
work in LabVIEW. If you ever have unexplainable trouble with data
acquisition in a LabVIEW program, use the Test Resources button
and the Test Panels button to make sure the device is working
properly.
Scales
Scales shows you all the currently configured custom scales and provides
utilities for testing and reconfiguring those custom scales. Scales also
provides access to the DAQ Custom Scales Wizard, which allows you to
create new custom scales.
DAQ Custom Scales Wizard
The DAQ Custom Scales Wizard is a utility that creates custom scales
you can use to determine scaling information for existing virtual
channels. Each custom scale can have its own name and description to
help you identify it.
A custom scale can be one of three types: linear, polynomial, or table.
• Linear—A scale that uses the formula y = mx + b.
• Polynomial—A scale that uses the formula
y = a0 + (a1 * x) + (a2 * x2) + … + (an* xn).
• Table—A scale in which you enter the raw value and the
corresponding scaled value in a table format.
Software
Software shows all the currently installed National Instruments software.
The icon for each software package is also a shortcut that you can use to
launch the software. The Software category also includes a Software
Update Agent. The purpose of the Software Update Agent is to check if
the National Instruments software is the latest version. If the software isn’t
the latest version, the Software Update Agent opens the Web page on
ni.com to download the latest version of the software.
Software Architecture for Windows
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The main component of NI-DAQ, the nidaq32.dll, makes function
calls directly to a DAQ device. The function that the nidaq32.dll
performs depends on where you access it from. Both MAX and
LabVIEW can talk to NI-DAQ. MAX is used primarily for
configuring and testing the DAQ device. MAX not only helps
configure devices, but it also tells you what devices are present in the
system. To do this, MAX must communicate with the Windows
Device Manager and the Windows Registry.
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Organization of Data Acquisition VIs
Most of the Data Acquisition VIs located on the Functions»Data
Acquisition palette are grouped in the following levels according to their
functionality:
• Easy VIs
• Intermediate VIs
• Utility VIs
• Advanced VIs
Easy VIs
Easy VIs perform simple DAQ operations and typically reside in the first
row of VIs in a palette. You can run these VIs from the front panel or use
them as subVIs in basic applications.
You need only one Easy VI to perform each basic DAQ operation. Unlike
Intermediate and Advanced VIs, Easy VIs automatically alert you to errors
with a dialog box that allows you to stop the execution of the VI or to
ignore the error.
Intermediate VIs
Intermediate VIs have more hardware functionality and efficiency in
developing applications than Easy VIs. Use Intermediate VIs in most
applications. Intermediate VIs give you more control over error handling
than Easy VIs. With each VI, you can check for errors or pass the error
cluster to other VIs.
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Utility VIs
Utility VIs are also intermediate-level VIs and thus have more hardware
functionality and efficiency in developing an application than Easy VIs.
Utility VIs consist of convenient groupings of Intermediate VIs. They are
for situations where you need more functionality control than the Easy I/O
VIs provide but want to limit the number of VIs you call.
Advanced VIs
Advanced VIs are the lowest-level interface to the DAQ driver. Very few
applications require the use of Advanced VIs. Advanced VIs return the
greatest amount of status information from the DAQ driver. Use
Advanced VIs when Easy or Intermediate VIs do not have the inputs
necessary to control an uncommon DAQ function.
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Homework Procedure
Part 1. Measurement & Automation Explorer (MAX)
In Part 1, you will become familiar with the installation and configuration
of a data acquisition device. This exercise also gives a detailed tour of
MAX.
1. Connect the sine wave from the function generator to analog in 1 on the
BNC-2120.
2. Connect analog out 0 to analog in 2.
3. Launch MAX by double-clicking the icon on the Windows desktop.
4. Double-click the Devices and Interfaces category. MAX searches for
installed hardware and lists the National Instruments devices found. A
device number in parentheses is assigned to each device in the system.
The LabVIEW DAQ VIs use this number to specify which device the VIs
address. If the device is not listed, go to View»Refresh.
5. Right-click the DAQ device folder for the specific device and select
Properties. A configuration dialog box appears.
The Configuration dialog box contains several tabs. The System tab
allows you to change the device number of the DAQ device. It also reports
the system resources assigned to the device through the Windows
Registry. The system resources shown in the Configuration dialog box
include the following items:
• Input/Output Range (Base I/O Address)—The DAQ device
communicates with the computer primarily through its registers.
The base I/O address setting determines where in the computer
I/O space the device registers reside.
• Interrupt Request (IRQ)—An interrupt gives the processor the ability
to respond quickly to its peripherals. Think of a processor interrupt as a
doorbell. If you did not have a doorbell, you would have to go to the door
periodically to see if anyone were there. With a doorbell, you need to go to
the door only when the doorbell rings, and you are confident that someone
is there waiting. Likewise, a DAQ device uses an interrupt as a doorbell to
tell the processor that it has data waiting to be read. Every device that uses
processor interrupts must be assigned a different interrupt level, or the
devices can conflict with each other.
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• Direct Memory Access (DMA)—DMA is a data transfer method in
which data is transferred directly from the peripheral to computer
memory, bypassing the processor. DMA is usually required to achieve
maximum data transfer speed, making it useful for high-speed DAQ
devices. DAQ devices that use the PCI bus have their own onboard DMA
channels, and the PCI bus handles the sharing of that DMA. DAQ devices
that use the AT/ISA bus must assign themselves a DMA channel from the
computer.
6. Select the Input/Output Range. Click View below the Resources dialog
box. You can use the dialog box that appears to configure non-Plug and
Play devices manually. If you have a Plug and Play device, the computer
automatically configures the system resources and the Input/Output Range
is dimmed.
7. Click the AI tab. This tab allows you to set the default polarity/range
and grounding mode used for analog input signals. These default values
are used by NI-DAQ as long as other settings do not override them.
8. Click the AO tab. This tab allows you to set the default analog output
polarity.
9. Click the Accessory tab to specify any accessories that are attached to
the DAQ device. Select the BNC-2120 from the list.
Devices on the Accessory list usually provide some form of signal
conditioning for signals, or they increase the number of channels you can
measure. If an accessory does not change the way signals are measured, it
does not appear on the Accessory list.
10. Click the OPC tab. The OPC tab allows you to set the recalibration
period when using an OPC server. The use of an OPC server is beyond the
scope of this lab.
11. Complete the following steps to verify the DAQ system is set up
correctly.
a. Click the System tab.
b. Click Test Resources. This action tests the system resources
assigned to the device.
c. Click OK.
12. On the System tab, click Run Test Panels. The following front panel
appears. The Analog Input tab allows you to read the analog input
channels. Channel 0 can be configured as the temperature sensor on the
BNC-2120. You should see a voltage between 0.2 and 0.3 V displayed on
the graph.
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13. Place your finger on the temperature sensor to increase the voltage.
14. On the Analog Input test panel, change the channel to 1. Make sure
that the sine wave from the function generator is connected to analog in 1
on the BNC-2120. The sine wave probably looks distorted.
In the lower left corner of the test panel, you can see the following three
options for Data Mode.
• Strip Chart: continuously displays data, scrolling as new data is
acquired.
• One Shot: displays only one screen of data.
• Continuous: continuously displays a screen of data at a time
One Shot and Continuous Data Modes allow you to adjust the
sample rate. The higher the sample rate, the more accurately the graph
displays the waveform.
15. Complete the following steps to make the graph look better.
a. On the BNC-2120, set the frequency range to 100 Hz – 10 kHz
and turn the Frequency Adjust to Lo.
b. On the test panel, change the Data Mode to One Shot or
Continuous and try different values such as 5,000, 10,000, or 15,000
for the sample rate until the graph displays a smooth sine wave.
16. Click the Analog Output tab. In this dialog box, you can set up a DC
voltage or sine wave on one of the analog output channels of the DAQ
device. Complete the following steps to output a DC voltage on channel 0.
a. Verify that analog out 0 is connected to analog in 2 on the BNC2120. DC Voltage should already be selected for the Output Mode.
b. Enter 5 V for the DC Voltage and click Update Channel.
17. Click the Analog Input tab. Change the channel to 2. You should now
see 5 V displayed on the graph. You can make the signal more readable by
selecting Strip Chart for the Data Mode. If you don’t see the change,
click Start.
18. Click the Counter I/O tab. Complete the following steps to verify
counter/timer operation, do the following:
a. Change the Counter Mode to Simple Event Counting. The counter
is now set up to count the pulses of a 100 kHz onboard signal.
b. Click Start. The Counter Value should increment rapidly.
c. Click Reset to stop the counter test.
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19. To increase the rate of the pulses, change the Event Source to
Internal 20 MHz Clock and click Start. Notice how much faster the
Counter Value increases. It increments faster because the pulses being
counted now occur at 20 MHz, instead of 100 kHz. Click Reset to stop the
counter.
20. Click the Digital I/O tab. This tab gives you access to the eight digital
lines on the device and allows you to set each line as an input or output
line.
21. Close the test panel and exit MAX.
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Part 2. Voltmeter VI
Complete the following steps to build a VI that measures the voltage that
the temperature sensor on the BNC-2120 returns. The temperature sensor
returns a voltage proportional to the temperature. The sensor is hardwired
to channel 0 of the BNC-2120.
1. Open a new VI and build the following front panel.
Configure the meter scale for 0.0 to 0.4. Use the Labeling tool to doubleclick 10.0 and type 0.4. You might need to enlarge the meter to display the
scale.
2. Build the following block diagram.
AI Sample Channel VI (Functions»Data Acquisition»Analog Input
palette)—Reads an analog input channel and returns the voltage.
Wait Until Next ms Multiple function (Functions»Time & Dialog
palette)—Causes the loop to execute every 100 ms.
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3. Save the VI as Voltmeter.vi.
4. Display the front panel and run the VI.
The meter displays the voltage the temperature sensor outputs. Place your
finger on the temperature sensor and notice that the voltage increases.
If an error occurs, the Easy I/O VIs display a dialog box showing the error
code and a description of the error.
5. Close the VI.
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Part 3. Buffered Acquisition VI
With a buffered acquisition, LabVIEW tells the DAQ device how many
points to acquire and at what rate to acquire them. Timing then becomes
the responsibility of the DAQ device. In a buffered acquisition, the DAQ
device controls all aspects of the acquisition. In contrast, with a softwaretimed acquisition, the computer is solely responsible for managing the
acquisition, which can be problematic if the computer suddenly cannot
give priority to the data acquisition process.
1. Open a new VI and build the following front panel.
You can create most of the front panel controls shown above from the
block diagram by right-clicking the appropriate terminals of the DAQ VIs
and selecting Create»Control.
In this exercise, you acquire data from one channel on the BNC-2120 and
display the data on the graph. Set the Scan Rate to 20000 and Buffer Size
to 1000. Set the DAQ Channel Name control to 1 and the Device to the
proper device number for your DAQ device.
2. Build the following block diagram.
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3. Save the VI as Buffered Acquisition.vi.
4. From the front panel, run the VI. You should see a sine wave plotted on
the waveform graph.
5. Close the VI.
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Part 4. Continuous Acquire with MIO VI
Complete the following steps to build a VI that performs a continuous
acquisition operation and plots the most recently acquired data on a chart.
1. Open a new VI and build the following front panel.
a. You can create most of the front panel controls on the block diagram
by right-clicking the appropriate terminals of the Data Acquisition
VIs and selecting Create»Control from the shortcut menu.
b. Acquire data from multiple channels of the BNC-2120 and display
the data on the graph. Set the Scan Rate to 1000 scans/s, buffer size
to 3000, and # of Scans to Read to 3000.
c. Set the channel string control input to 0,1,2 or 0:2.
d. Make the following connections on the BNC-2120.
• Connect the sine wave output to analog input CH1.
• Connect the square wave output to analog input CH2.
2. Build the following block diagram.
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3. Save the VI as Continuous Acquire with MIO.vi.
4. Display the front panel. Run the VI and monitor the data plotted on the
graph as you change the frequency knob on the BNC-2120.
The numeric constant of 0 you wired to the number of scans to acquire
input of AI Start enables a continuous or circular DAQ. Data fill a buffer
of fixed size in memory and then, on reaching the end of the buffer,
overwrite values from the beginning of the buffer.
5. Run the VI and monitor Scan Backlog as you decrease the scan rate or
the number of scans to read at a time. Scan backlog is defined as the
number of scans acquired into the acquisition buffer but not read. Scan
backlog is a measure of how well you are keeping up with a continuous
acquisition. If scan backlog steadily increases, you are not reading data
fast enough from the buffer and will eventually lose data. If this happens,
AI Read VI returns an error.
6. Close the VI.
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Lab Report
For your lab report, email the VIs and the answers to the questions below
to the instructor no later than <date>.
Data Sheet
Questions
1. What are the three methods that DAQ devices can be grounded?
2. Describe three uses of Measurement & Automation Explorer.
3. What are the differences and similarities between single-point
acquisition, continuous acquisition, and buffered acquisition?
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