USER GUIDE AND SPECIFICATIONS
NI cDAQ-9172
DeutschFrançais
ni.com/manuals
Contents
Introduction.............................................................................................4
Safety Guidelines .................................................................................... 5
Safety Guidelines for Hazardous Voltages...................................... 5
Related Documentation........................................................................... 6
Device Documentation and Specifications ...................................... 9
Training Courses.............................................................................. 9
Technical Support on the Web......................................................... 9
Installing the Software ............................................................................ 10
Installing NI-DAQmx ...................................................................... 10
Installing Other Software................................................................. 10
Installing the NI cDAQ-9172.................................................................. 11
Mounting the NI cDAQ-9172.......................................................... 12
NI 9901 Desktop Mounting Kit................................................ 12
NI 9910 DIN-Rail Kit............................................................... 13
NI 9905 Panel Mount Kit ......................................................... 13
Setting Up the NI cDAQ-9172................................................................15
Understanding LED Indications.............................................................. 17
Active LED ...................................................................................... 17
Ready LED ...................................................................................... 17
Using the NI cDAQ-9172 ....................................................................... 18
C Series I/O Modules....................................................................... 18
Correlated vs. Static DIO Modules...........................................19
cDAQ Module Interface .................................................................. 19
USB-STC2 ....................................................................................... 19
AI and AO Sample Timing....................................................... 19
Triggering Modes .....................................................................19
Independent Data Streams ........................................................19
PFI Signals................................................................................ 20
Flexible Counter/Timers........................................................... 20
Analog Input ............................................................................................20
Analog Input Triggering...................................................................20
AI Start Trigger Signal..............................................................21
AI Reference Trigger Signal .....................................................22
AI Pause Trigger Signal ............................................................24
Analog Input Timing Signals ...........................................................24
AI Sample Clock .......................................................................24
AI Sample Clock Timebase.......................................................25
Convert Behavior For Analog Input Modules...........................25
Getting Started with AI Applications in Software ...........................28
Analog Output .........................................................................................28
Analog Output Data Generation Methods ........................................28
Software-Timed Generations ....................................................29
Hardware-Timed Generations ...................................................29
Analog Output Triggering ................................................................30
Analog Output Timing Signals.........................................................31
AO Sample Clock......................................................................31
AO Start Trigger Signal ............................................................31
AO Pause Trigger Signal...........................................................33
Minimizing Glitches on the Output Signal.......................................34
Getting Started with AO Applications in Software..........................34
Digital I/O................................................................................................35
Correlated vs. Static DIO Modules ..................................................35
Static DIO.........................................................................................36
Digital Waveform Acquisition (Correlated Input) ...........................36
DI Sample Clock Signal............................................................36
Digital Waveform Generation (Correlated Output) .........................37
Buffered Digital Waveform Generation....................................38
Change Detection Event ...................................................................39
Routing Change Detection Event to an Output Terminal .........39
Change Detection Acquisition..........................................................39
Digital Input/Output Configuration for NI 9401 ..............................39
PFI ...........................................................................................................40
Counters...................................................................................................40
Counter Input Applications ..............................................................42
Counting Edges .........................................................................42
Pulse-Width Measurement ........................................................44
Period Measurement..................................................................46
Semi-Period Measurement ........................................................48
Frequency Measurement ...........................................................49
Position Measurement ...............................................................54
Two-Signal Edge-Separation Measurement..............................57
Counter Output Applications............................................................59
Simple Pulse Generation ...........................................................59
Pulse Train Generation..............................................................61
Frequency Generation ...............................................................62
Frequency Division ...................................................................63
NI cDAQ-9172 User Guide and Specifications 2 ni.com
Counter Timing Signals................................................................... 63
Counter n Source Signal ........................................................... 64
Counter n Gate Signal............................................................... 65
Counter n Aux Signal ............................................................... 65
Counter n A, Counter n B, and Counter n Z Signals ................ 66
Counter n Up_Down Signal ..................................................... 66
Counter n HW Arm Signal .......................................................66
Counter n Internal Output and Counter n TC Signals ..............67
Frequency Output Signal .......................................................... 67
Default Counter/Timer Routing.......................................................68
Counter Triggering .......................................................................... 68
Other Counter Features.................................................................... 69
Cascading Counters .................................................................. 69
Counter Filters .......................................................................... 69
Prescaling.................................................................................. 70
Duplicate Count Prevention...................................................... 71
Synchronization Modes ............................................................73
Digital Routing and Clock Generation.................................................... 75
Clock Routing .................................................................................. 76
80 MHz Timebase .................................................................... 76
20 MHz Timebase .................................................................... 76
100 kHz Timebase .................................................................... 76
Specifications .......................................................................................... 77
Analog Input .................................................................................... 77
Analog Output.................................................................................. 77
Digital Waveform Characteristics (Slots 1 through 4 Only) ........... 78
PFI Characteristics (Slots 5 and 6 Only) ......................................... 78
General-Purpose Counter/Timers (Slots 5 and 6 Only)................... 79
Frequency Generator (Slots 5 and 6 Only) ...................................... 80
External Digital Triggers (Slots 5 and 6 or with Some
AI Modules) .................................................................................. 80
Module I/O States ............................................................................ 80
Power Requirements ........................................................................ 80
Bus Interface ....................................................................................81
Physical Characteristics ................................................................... 81
Safety ...............................................................................................81
Environmental..................................................................................82
Shock and Vibration ........................................................................82
Electromagnetic Compatibility ........................................................ 83
CE Compliance ................................................................................ 83
Environmental Management............................................................ 83
Where to Go for Support......................................................................... 84
© National Instruments Corporation 3 NI cDAQ-9172 User Guide and Specifications
Introduction
This user guide describes how to use the National Instruments cDAQ-9172
chassis and lists specifications. For an interactive demonstration of how to
install the NI cDAQ-9172, go to
ni.com/info and enter daqinstall.
The NI cDAQ-9172 is an eight-slot USB chassis designed for use
with C Series I/O modules. The NI cDAQ-9172 chassis is capable of
measuring a broad range of analog and digital I/O signals and sensors using
a Hi-Speed USB 2.0 interface. For module specifications, refer to the
documentation included with your C Series I/O module(s) or go to
ni.com/manuals.
1
2
NI cDAQ-9172
Ready
Active
3
11-30 VDC
15 W
1 Power Switch
2 Ready/Active LEDs
3 Power Connector
4 USB Connector
ON
OFF
12345
4 5 6
5 Empty Module Slots
6 Installed C Series I/O Modules
7 Screw for Ground Connection
Figure 1. NI cDAQ-9172 Chassis
7
NI cDAQ-9172 User Guide and Specifications 4 ni.com
Safety Guidelines
Operate the NI cDAQ-9172 chassis only as described in this user guide.
Note Because some C Series I/O modules may have more stringent certification standards
than the NI cDAQ-9172 chassis, the combined system may be limited by individual
component restrictions. Refer to the Using the NI cDAQ-9172 section of this document for
more details.
Caution The NI cDAQ-9172 chassis is not certified for use in hazardous locations.
Hot Surface This icon denotes that the component may be hot. Touching this component
may result in bodily injury.
Safety Guidelines for Hazardous Voltages
If hazardous voltages are connected to the module, take the following
precautions. A hazardous voltage is a voltage greater than 42.4 V
60 VDC to earth ground.
Caution Ensure that hazardous voltage wiring is performed only by qualified personnel
adhering to local electrical standards.
Caution Do not mix hazardous voltage circuits and human-accessible circuits on the same
module.
or
pk
Caution Make sure that chassis and circuits connected to the module are properly
insulated from human contact.
Caution The NI cDAQ-9172 chassis provides no isolation, but some modules offer
isolation. Follow the safety guidelines for each module when using hazardous voltage.
© National Instruments Corporation 5 NI cDAQ-9172 User Guide and Specifications
Related Documentation
Each application software package and driver includes information about
writing applications for taking measurements and controlling measurement
devices. Check
documentation, and refer to Table 1 for a list of locations for driver and
application software documentation. The following document location
references assume you have NI-DAQmx 8.8 or later, and where applicable,
version 7.1 or later of the NI application software.
Table 1. NI Driver and Application Software Documentation
Software Document/Description Location/Topic
ni.com/manuals for the most recent hardware
NI-DAQmx for Windows DAQ Getting Started
Guide—describes how to
install and use the
NI-DAQmx driver software
for Windows and your data
acquisition (DAQ) device,
how to confirm the device is
operating properly, and how
to take an NI-DAQmx
measurement.
NI-DAQ Readme—includes
information about
NI-DAQmx and Traditional
NI-DAQ (Legacy).
Describes how to choose
the API to use, new
features, and a list of known
issues, supported devices,
and devices not supported.
Also provides details about
system requirements.
NI-DAQmx Help—explains
how to get started in your
OS and ADE; provides an
NI-DAQmx overview;
includes information about
programming the most
common measurement
tasks with references to
examples in CVI/C, C++,
.NET.
Start»Programs»
National Instruments»
NI-DAQ»DAQ Getting Started
Guide
Start»Programs»
National Instruments»
NI-DAQ»NI-DAQ Readme
Start»Programs»
National Instruments»
NI-DAQ»NI-DAQmx Help
NI cDAQ-9172 User Guide and Specifications 6 ni.com
Table 1. NI Driver and Application Software Documentation (Continued)
Software Document/Description Location/Topic
LabVIEW Getting Started with
LabVIEW—describes the
LabVIEW graphical
programming environment
and the basic LabVIEW
features you use to build
data acquisition and
instrument control
application.
LabVIEW Help—provides
information about
LabVIEW programming
concepts, step-by-step
instructions for using
LabVIEW, and reference
information about
LabVIEW VIs, functions,
palettes, menus, and tools.
LabVIEW Help Topics Specific to NI-DAQmx
Includes overview
information and a tutorial to
learn how to take an
NI-DAQmx measurement
in LabVIEW using the
DAQ Assistant.
Start»All Programs»
National Instruments»
LabVIEW»LabVIEW Manuals or
navigate to the
labview\manuals
directory and opening
LV_Getting_Started.pdf
Help»Search the LabVIEW Help
From the Contents tab, Getting
Started»Getting Started with DAQ
Describes the LabVIEW
NI-DAQmx VIs and
properties.
From the Contents tab, VI and
Function Reference»
Measurement I/O VIs and
Functions
Contains the conceptual
and how-to information you
From the Contents tab, Taking
Measurements
need to acquire and analyze
measurement data in
LabVIEW, including
common measurements,
measurement
fundamentals, NI-DAQmx
key concepts, and device
considerations.
© National Instruments Corporation 7 NI cDAQ-9172 User Guide and Specifications
Table 1. NI Driver and Application Software Documentation (Continued)
Software Document/Description Location/Topic
LabWindows™/CVI
™
LabWindows/CVI Help
Data Acquisition
book—contains
NI-DAQmx measurement
concepts and step-by-step
Help»Contents, then select Using
LabWindows/CVI»
Data Acquisition»Taking an
NI-DAQmx Measurement in
LabWindows/CVI
instructions about creating
a measurement task using
the DAQ Assistant.
Measurement
Studio/Microsoft Visual
Studio .NET
ANSI C without
NI Application Software
LabWindows/CVI Help
NI-DAQmx Library
LibraryReference»
NI-DAQmx Library
book—contains
NI-DAQmx API overviews
and function reference.
Microsoft Visual Studio
.NET Help/NI
Measurement Studio
Help—contains
NI-DAQmx methods and
Measurement Studio»
NI Measurement Studio Help and
select NI-DAQmx .NET Class
Library or NI-DAQmx Visual C++
Class Library
properties.
NI-DAQmx Help Start»All Programs»
National Instruments»
NI-DAQ»NI-DAQmx Help
NI-DAQmx C Reference
Help—describes the
NI-DAQmx Library
functions.
Start»All Programs»
National Instruments»
NI-DAQ»NI-DAQmx C Reference
Help
NI cDAQ-9172 User Guide and Specifications 8 ni.com
Table 1. NI Driver and Application Software Documentation (Continued)
Software Document/Description Location/Topic
.NET Languages without
NI Application Software
NI-DAQmx .NET
*
Help—contains conceptual
topics for using NI-DAQmx
with Visual C# and Visual
Basic .NET.
Start»All Programs»
National Instruments»
NI-DAQ»NI-DAQmx .NET
Reference Help. Expand
NI Measurement Studio Help»
NI Measurement Studio .NET
Class Library»Reference to view
the function reference. Expand
NI Measurement Studio Help»
NI Measurement Studio .NET
Class Library»Using the
Measurement Studio .NET Class
Libraries
Visual Studio .NET
Help—contains conceptual
topics for using NI-DAQmx
with Visual C# and Visual
Basic .NET.
*
With the Microsoft .NET Framework version 1.1 or later, you can use NI-DAQmx to create applications using Visual C#
and Visual Basic .NET without Measurement Studio. You need Microsoft Visual Studio .NET 2003 or Microsoft Visual
Studio 2005 for the API documentation to be installed.
Help»Contents. Select
Measurement Studio from the
Filtered By drop-down list and
follow the location instructions for
the NI-DAQmx .NET Help.
Device Documentation and Specifications
Check ni.com/manuals for the most recent device and software
documentation. If you do not have Web access, NI-DAQmx includes a
Documentation CD that includes documentation available when
NI-DAQmx released.
Training Courses
If you need more help getting started developing an application with
NI products, NI offers training courses. To enroll in a course or obtain
a detailed course outline, refer to
ni.com/training.
Technical Support on the Web
For additional support, refer to ni.com/support or zone.ni.com.
© National Instruments Corporation 9 NI cDAQ-9172 User Guide and Specifications
Installing the Software
Installing NI-DAQmx
The DAQ Getting Started Guide, which you can download at ni.com/
manuals
software and hardware, configuring channels and tasks, and getting started
developing an application.
Installing Other Software
If you are using other software, refer to the installation instructions that
accompany your software.
, offers NI-DAQmx users step-by-step instructions for installing
NI cDAQ-9172 User Guide and Specifications 10 ni.com
Installing the NI cDAQ-9172
Figure 2 shows the dimensions of the NI cDAQ-9172 chassis.
88.1 mm
(3.50 in.)
46.0 mm
(1.81 in.)
24.8 mm
(0.98 in.)
59.6 mm
(2.35 in.)
NI cDAQ-9172
Ready
Active
11-30 VDC
15 W
53.8 mm
(2.12 in.)
165.1 mm
(6.50 in.)
ON
OFF
254.0 mm
(10.00 in.)
23.7 mm
(0.94 in.)
20.3 mm
(0.80 in.)
25.0 mm
(0.98 in.)
44.1 mm
(1.74 in.)
63.1 mm
(2.49 in.)
8 7 6 5 4 3 2 1
19.0 mm
(0.75 in.)
36.4 mm
(1.43 in.)
51.7 mm
(2.04 in.)
4.10 mm
(0.16 in.)
44.1 mm
(1.74 in.)
58.9 mm
(2.32 in.)
31.7 mm
(1.25 in.)
19.1 mm
(0.75 in.)
23.2 mm
(0.91 in.)
Figure 2. NI cDAQ-9172 with Dimensions in Millimeters (Inches)
© National Instruments Corporation 11 NI cDAQ-9172 User Guide and Specifications
Mounting the NI cDAQ-9172
You can mount the NI cDAQ-9172 chassis using a desktop, a 35 mm
DIN-Rail, or a panel mount accessory kit. For accessory ordering
information, refer to
Caution Your installation must meet the following requirements:
• Allows 25.4 mm (1 in.) of clearance above and below the NI cDAQ-9172 chassis for
air circulation.
• Allows at least 50.8 mm (2 in.) of clearance in front of the modules for common
connector cabling such as the 10-terminal detachable screw terminal connector and, as
needed, up to 88.9 mm (3.5 in.) of clearance in front of the modules for other types of
cabling. For more information about mechanical dimensions, refer to
info
and enter the info code cDAQMechanical. For more information about cable
dimensions, refer to
ni.com/info and enter the info code cDAQCable.
NI 9901 Desktop Mounting Kit
The NI 9901 Desktop Mounting Kit includes two metal feet you can install
on the sides of the NI cDAQ-9172 chassis for desktop use. With this kit,
you can tilt the NI cDAQ-9172 chassis for convenient access to the I/O
module connectors. When you install the two metal feet, the two existing
screws on the power switch side of the chassis must be removed. After
removing the screws, replace them with the two longer screws included in
the NI 9901 Desktop Mounting Kit.
ni.com.
ni.com/
Figure 3. NI 9901 Desktop Mounting Kit
NI cDAQ-9172 User Guide and Specifications 12 ni.com
NI 9910 DIN-Rail Kit
The NI 9910 DIN-Rail Kit contains one clip for mounting the chassis on a
standard 35 mm DIN-Rail. To mount the chassis on a DIN-Rail, fasten the
DIN-Rail clip to the chassis using a number 2 Phillips screwdriver and
two M4 × 17 screws. The screws are included in the DIN-Rail kit. Make
sure the DIN-Rail kit is installed as illustrated in Figure 4, with the larger
lip of the DIN-RAIL positioned up. When the DIN-Rail kit is properly
installed, the NI cDAQ-9172 chassis is centered on the DIN-Rail.
Caution Remove the I/O modules before removing the chassis from the DIN-Rail.
Figure 4. DIN-Rail Installation on the NI cDAQ-9172
NI 9905 Panel Mount Kit
To mount the chassis on a panel, align the chassis on the panel mount
accessory. Attach the chassis to the panel mount kit using two M4 × 17
screws (as shown in Figure 5). National Instruments provides these screws
with the panel mount kit. You must use these screws because they are the
correct depth and thread for the panel. These slots in the panel mount kit
© National Instruments Corporation 13 NI cDAQ-9172 User Guide and Specifications
can be used with M4, M5, No. 8, or No.10 panhead screws. Figure 5
illustrates the panel dimensions and installation on the NI cDAQ-9172
chassis. Refer to the documentation included with the NI 9905 Panel
Mount Kit for more detailed dimensions.
330.2 mm
(13.00 in.)
NATIONAL
INSTRUMENTS
NI cDAQ-9172
11-30 VDC
Ready
Active
15 W
ON
OFF
48.1 mm
(1.90 in.)
28.1 mm
(1.11 in.)
87654321
88.1 mm
(3.47 in.)
Figure 5. Panel Mount Dimensions and Installation on the NI cDAQ-9172
NI cDAQ-9172 User Guide and Specifications 14 ni.com
Setting Up the NI cDAQ-9172
Complete the following steps to prepare the NI cDAQ-9172 chassis for use:
1. Before connecting the hardware, install the NI-DAQmx software.
Refer to the DAQ Getting Started Guide for more information about
software installation.
Note The NI-DAQmx software is included on the CD shipped with your kit and is
available for download at
after installation from Start»All Programs»National Instruments»NI-DAQ»DAQ
Getting Started Guide. Other NI documentation is available from
2. If you are not using any mounting accessories, attach the provided
3. Make sure the NI cDAQ-9172 chassis power switch is turned off.
4. Attach a ring lug to a 14 AWG (1.6 mm) wire. Connect the ring lug to
ni.com/support. The DAQ Getting Started Guide is available
rubber standoffs to the back of the NI cDAQ-9172 chassis.
the ground terminal on the side of the chassis using the ground screw.
Attach the other end of the wire to the system safety ground.
ni.com/manuals.
1
1 Attached to System Ground
Figure 6. Ring Lug Attached to Ground Terminal
Note
Additionally, attach a wire with a ring lug to all other C Series I/O module cable
shields. You must connect this wire to the ground terminal of the chassis using the ground
screw.
5. Remove the plastic cover from the connector in any empty module slot.
© National Instruments Corporation 15 NI cDAQ-9172 User Guide and Specifications
6. Squeeze both C Series I/O module latches, insert the I/O module into
the module slot, and press until both latches lock the module in place.
7. Connect the NI cDAQ-9172 chassis with the supplied USB cable to
any available USB port on your computer.
8. Connect the power source to the NI cDAQ-9172 chassis. The
NI cDAQ-9172 chassis requires an external power supply that meets
the specifications in the Power Requirements section.
Note The NI cDAQ-9172 chassis uses a DC input jack with a locking ring. Use only this
connector with the NI cDAQ-9172 chassis. Refer to the Specifications section for more
information about the connector.
9. Secure the power supply and USB cables, as depicted in Figure 7,
using the two tie wraps and adhesive tie wrap mounts included in the
shipping kit. The tie wraps and adhesive mounts help secure the
non-latching USB connection. They can also be used to route the
cables to a desirable position.
NI cDAQ-9172
Figure 7. cDAQ Chassis With Secured Cables
10. Power on the NI cDAQ-9172 chassis.
11. Double-click the Measurement & Automation icon, shown at left,
on the desktop to open MAX.
12. Expand Devices and Interfaces, and then expand NI-DAQmx
Devices.
NI cDAQ-9172 User Guide and Specifications 16 ni.com
13. Check that your device appears under Devices and Interfaces. If your
device does not appear, press <F5> to refresh the view in MAX. If your
device is still not recognized, refer to
troubleshooting information.
14. Right-click your device and select Self-Test.
If you need help during the self-test, select Help»Help Topics»
NI-DAQmx and click MAX Help for NI-DAQmx.
When the self-test finishes, a message indicates successful verification
or an error. If an error occurs, refer to
for troubleshooting information.
Note When in use, the NI cDAQ-9172 chassis may become warm to the touch. This is
normal.
Understanding LED Indications
Active LED
The Active LED indicates whether the NI cDAQ-9172 chassis is
communicating over the USB bus.
ni.com/support/install for
ni.com/support/install
Table 2. Active LED
Ready LED
LED Definition
Amber Power is applied, but USB connection is not
established
Green USB traffic present
Off No USB traffic present
The Ready LED is lit when the NI cDAQ-9172 chassis is ready for use. The
color indicates whether the USB connection is Full-Speed or Hi-Speed.
Table 3. Ready LED
LED Definition
Amber Hi-Speed (480 Mbit/sec)
Green Full-Speed (12 Mbit/sec)
Off USB connection is not established
© National Instruments Corporation 17 NI cDAQ-9172 User Guide and Specifications
Using the NI cDAQ-9172
The cDAQ system consists of three parts: C Series I/O modules, the cDAQ
module interface, and the USB-STC2. These components digitize signals,
perform D/A conversions to generate analog output signals, measure and
control digital I/O signals, and provide signal conditioning.
C Series
I/O Module
cDAQ Module
Interface
C Series
I/O Module
C Series
I/O Module
USB-
STC2
Figure 8. NI cDAQ-9172 Block Diagram
USB
2.0
C Series I/O Modules
National Instruments C Series I/O modules provide built-in signal
conditioning and screw terminal, spring terminal, BNC, D-SUB, or
RJ-50 connectors. A wide variety of I/O types are available, allowing
you to customize the cDAQ system to meet your application needs.
C Series I/O modules are hot-swappable and automatically detected by the
NI cDAQ-9172 chassis. I/O channels are accessible using the NI-DAQmx
driver software.
Because the modules contain built-in signal conditioning for extended
voltage ranges or industrial signal types, you can usually make your
wiring connections directly from the C Series I/O modules to your
sensors/actuators. In most cases, the C Series I/O modules provide isolation
from channel-to-earth ground.
For more information about which C Series I/O modules are compatible
with the NI cDAQ-9172 chassis, refer to the KnowledgeBase document,
C Series Modules Supported in the NI cDAQ-9172 CompactDAQ.
NI cDAQ-9172 User Guide and Specifications 18 ni.com
To access this KnowledgeBase, go to ni.com/info and enter the info
code
Correlated vs. Static DIO Modules
Digital I/O module capabilities are determined by the type of digital signals
that the module is capable of measuring or generating. Static digital I/O
modules are designed for signals that change slowly and are accessed by
software-timed reads and writes. Correlated digital I/O modules are for
signals that change rapidly and are updated by either software-timed or
hardware-timed reads and writes. For more information about Digital I/O
modules, refer to the Digital I/O section.
cDAQ Module Interface
The cDAQ Module Interface manages data transfers between the
USB-STC2 and the C Series I/O modules. The interface also handles
autodetection, signal routing, and synchronization.
USB-STC2
The USB-STC2 features independent high-speed data streams; flexible
AI and AO sample timing; triggering; PFI signals for multi-device
synchronization; flexible counter/timers with hardware gating; digital
waveform acquisition and generation; and static DIO.
rdcdaq.
AI and AO Sample Timing
The USB-STC2 contains advanced analog input and analog output timing
engines. A wide range of timing and synchronization signals are available
through the PFI lines. Refer to the Analog Input Timing Signals and
Analog Output Timing Signals sections for more information about the
configuration of these signals.
Triggering Modes
The NI cDAQ-9172 supports different trigger modes, such as start trigger,
reference trigger, and pause trigger with analog, digital, or software
sources. Refer to the Analog Input Triggering and Analog Output
Triggering sections for more information.
Independent Data Streams
The NI cDAQ-9172 supports four independent high-speed data streams;
allowing for up to four simultaneous hardware timed tasks, such as analog
input, analog output, buffered counter/timers, and correlated digital
input/output.
© National Instruments Corporation 19 NI cDAQ-9172 User Guide and Specifications
Analog Input
PFI Signals
The PFI signals, available through correlated digital input and output
modules installed in slots 5 and/or 6, provide access to advanced features
such as triggering, synchronization, and counter/timers. Refer to the PFI
section for more information.
The PFI pins have a digital filter circuit at the inputs that is configurable on
a per-line basis. The filters allow the rejection of noise caused by noisy
environments, bounces on switches, and so on.
Flexible Counter/Timers
The NI cDAQ-9172 includes two general-purpose 32-bit counter/timers
that can be used to count edges, measure pulse-widths, measure periods and
frequencies, and perform position measurements (encoding). In addition,
the counter/timers can generate pulses, pulse trains, and square waves with
adjustable frequencies. You can access the counter inputs and outputs using
correlated digital I/O modules in slots 5 and/or 6. Refer to the Counters
section for more information.
To perform analog input measurements, insert a supported analog input
C Series I/O module into any slot on the cDAQ chassis. The measurement
specifications, such as number of channels, channel configuration, sample
rate, and gain, are determined by the type of C Series I/O module used. For
more information and wiring diagrams, refer to the documentation included
with your C Series I/O modules.
The NI cDAQ-9172 has one AI timing engine, which means that only
one analog input task can be running at a time on a chassis. However, the
analog input task can include channels from multiple analog input modules.
Analog Input Triggering
A trigger is a signal that causes an action, such as starting or stopping the
acquisition of data. When you configure a trigger, you must decide how
you want to produce the trigger and the action you want the trigger to cause.
The NI cDAQ-9172 chassis supports internal software, external digital
triggering, and analog triggering.
Three triggers are available: start trigger, reference trigger, and pause
trigger. An analog or digital trigger can initiate these three trigger actions.
Any C Series correlated digital input module can supply a digital trigger
when installed in slots 5 or 6, and some C Series analog modules can supply
an analog or digital trigger in any slot. The start, reference, and pause
NI cDAQ-9172 User Guide and Specifications 20 ni.com
triggers can come from three separate modules if desired. To find your
module triggering options, refer to the documentation included with your
C Series I/O modules. For more information about using digital modules
for triggering, refer to the Digital I/O section.
AI Start Trigger Signal
Use the AI Start Trigger (ai/StartTrigger) signal to begin a measurement
acquisition. A measurement acquisition consists of one or more samples. If
you do not use triggers, begin a measurement with a software command.
Once the acquisition begins, configure the acquisition to stop in one of the
following ways:
• When a certain number of points is sampled (in finite mode)
• After a hardware reference trigger (in finite mode)
• With a software command (in continuous mode)
An acquisition that uses a start trigger (but not a reference trigger) is
sometimes referred to as a posttriggered acquisition. That is, samples are
measured only after the trigger.
When you are using an internal sample clock, you can specify a delay from
the start trigger to the first sample.
Using a Digital Source
To use ai/StartTrigger with a digital source, specify a source and an edge.
Use the following signals as the source:
•Any PFI terminal.
• Counter n Internal Output
The source also can be one of several other internal signals on your
NI cDAQ-9172 chassis. Refer to the Device Routing in MAX topic in the
NI-DAQmx Help or the LabVIEW Help in version 8.0 or later for more
information.
The NI-DAQmx Help is available after installation from Start»
All Programs»National Instruments»NI-DAQ»NI-DAQmx Help.
To view the LabVIEW Help, in version 8.0 or later, select Help»
Search the LabVIEW Help in LabVIEW. Alternately, to download
the LabVIEW Help, go to
You also can specify whether the measurement acquisition begins on the
rising edge or falling edge of ai/StartTrigger.
© National Instruments Corporation 21 NI cDAQ-9172 User Guide and Specifications
ni.com/manuals.
Using an Analog Source
Some C Series I/O modules can generate a trigger based on an analog
signal. In NI-DAQmx, this is called the Analog Comparison Event.
When you use an analog trigger source for ai/StartTrigger, the acquisition
begins on the first rising edge of the Analog Comparison Event signal.
Routing AI Start Trigger to an Output Terminal
You can route ai/StartTrigger to any output PFI terminal. The output is an
active high pulse.
AI Reference Trigger Signal
Use a reference trigger (ai/ReferenceTrigger) signal to stop a measurement
acquisition. To use a reference trigger, specify a buffer of finite size and
a number of pretrigger samples (samples that occur before the reference
trigger). The number of posttrigger samples (samples that occur after the
reference trigger) desired is the buffer size minus the number of pretrigger
samples.
Once the acquisition begins, the NI cDAQ-9172 chassis writes samples to
the buffer. After the NI cDAQ-9172 chassis captures the specified number
of pretrigger samples, the NI cDAQ-9172 chassis begins to look for the
reference trigger condition. If the reference trigger condition occurs before
the NI cDAQ-9172 captures the specified number of pretrigger samples, the
NI cDAQ-9172 ignores the condition.
If the buffer becomes full, the NI cDAQ-9172 continuously discards the
oldest samples in the buffer to make space for the next sample. This data
can be accessed (with some limitations) before the NI cDAQ-9172 chassis
discards it. Refer to the KnowledgeBase document, Can a Pretriggered
Acquisition be Continuous?, for more information. To access this
KnowledgeBase, go to
NI cDAQ-9172 User Guide and Specifications 22 ni.com
ni.com/info and enter the info code rdcanq.
When the reference trigger occurs, the NI cDAQ-9172 continues to write
samples to the buffer until the buffer contains the number of posttrigger
samples desired. Figure 9 shows the final buffer.
Reference Trigger
Pretrigger Samples
Complete Buffer
Figure 9. Reference Trigger Final Buffer
Posttrigger Samples
Using a Digital Source
To use ai/ReferenceTrigger with a digital source, specify a source and an
edge. Either PFI or one of several internal signals on the NI cDAQ-9172
chassis can provide the source. Refer to the Device Routing in MAX topic
in the NI-DAQmx Help or the LabVIEW Help in version 8.0 or later for
more information.
The NI-DAQmx Help is available after installation from Start»
All Programs»National Instruments»NI-DAQ»NI-DAQmx Help.
To view the LabVIEW Help, in version 8.0 or later, select Help»
Search the LabVIEW Help in LabVIEW. Alternately, to download
the LabVIEW Help, go to
You also can specify whether the measurement acquisition stops on the
rising edge or falling edge of ai/ReferenceTrigger.
ni.com/manuals.
Using an Analog Source
Some C Series I/O modules can generate a trigger based on an analog
signal. In NI-DAQmx, this is called the Analog Comparison Event.
When you use an analog trigger source, the acquisition stops on the first
rising or falling edge of the Analog Comparison Event signal, depending
on the trigger properties.
Routing AI Reference Trigger Signal to an Output Terminal
You can route ai/ReferenceTrigger to any output PFI terminal.
© National Instruments Corporation 23 NI cDAQ-9172 User Guide and Specifications
AI Pause Trigger Signal
You can use the AI Pause Trigger (ai/PauseTrigger) signal to pause and
resume a measurement acquisition. The internal sample clock pauses while
the external trigger signal is active and resumes when the signal is inactive.
You can program the active level of the pause trigger to be high or low.
Using a Digital Source
To use ai/PauseTrigger, specify a source and a polarity. The source
can be either from PFI or one of several other internal signals on
your NI cDAQ-9172 chassis. Refer to the Device Routing in MAX topic in
the NI-DAQmx Help or the LabVIEW Help in version 8.0 or later for more
information.
The NI-DAQmx Help is available after installation from Start»
All Programs»National Instruments»NI-DAQ»NI-DAQmx Help.
To view the LabVIEW Help, in version 8.0 or later, select Help»
Search the LabVIEW Help in LabVIEW. Alternately, to download
the LabVIEW Help, go to
Using an Analog Source
Some C Series I/O modules can generate a trigger based on an analog
signal. In NI-DAQmx, this is called the Analog Comparison Event.
ni.com/manuals.
When you use an analog trigger source, the internal sample clock pauses
when the Analog Comparison Event signal is low and resumes when the
signal goes high (or vice versa).
Note Pause triggers are only sensitive to the level of the source, not the edge.
Analog Input Timing Signals
AI Sample Clock
A sample consists of one reading from each channel in the AI task.
ai/SampleClock signals the start of a sample of all analog input channels
in the task. ai/SampleClock can be generated from external or internal
sources.
NI cDAQ-9172 User Guide and Specifications 24 ni.com
k
PFI
Analog Comparison
Event
20 MHz Timebase
100 kHz Timebase
PFI
Analog Comparison Event
Ctr
n
Sigma-Delta Module Internal Output
ai/SampleClock
Timebase
Programmable
Divider
Figure 10. Sample Clock Timing Options
Internal Output
Clock
ai/SampleCloc
Routing AI Sample Clock to an Output Terminal
You can route ai/SampleClock to any output PFI terminal.
AI Sample Clock Timebase
The AI Sample Clock Timebase (ai/SampleClockTimebase) signal is
divided down to provide a source for ai/SampleClock. ai/SampleClock
Timebase can be generated from external or internal sources.
ai/SampleClockTimebase is not available as an output from the chassis.
Convert Behavior For Analog Input Modules
Scanned
Scanned C Series analog input modules contain a single A/D converter and
a multiplexer to select between multiple input channels. When the cDAQ
Module Interface receives a Sample Clock pulse, it begins generating a
Convert Clock for each scanned module in the current task. Each Convert
Clock signals the acquisition of a single channel from that module. The
Convert Clock rate depends on the module being used, the number of
channels used on that module, and the system Sample Clock rate.
The driver chooses the fastest conversion rate possible based on the speed
of the A/D converter for each module and adds 10 µs of padding between
each channel to allow for adequate settling time. This scheme enables the
channels to approximate simultaneous sampling. If the AI Sample Clock
rate is too fast to allow for 10 µs of padding, NI-DAQmx selects a
conversion rate that spaces the AI Convert Clock pulses evenly throughout
the sample. NI-DAQmx uses the same amount of padding for all the
modules in the task. To explicitly specify the conversion rate, use the
© National Instruments Corporation 25 NI cDAQ-9172 User Guide and Specifications
ActiveDevs and AI Convert Clock Rate properties using the DAQmx
Timing property node or functions.
Simultaneous Sample-and-Hold
Simultaneous sample-and-hold (SSH) C Series analog input modules
contain multiple A/D converters or circuitry that allows all the input
channels to be sampled at the same time. These modules sample their
inputs on every Sample Clock pulse.
Sigma-Delta
Sigma-delta C Series analog input modules function much like SSH
modules, but use A/D converters that require a high-frequency oversample
clock to produce accurate, synchronized data. Sigma-delta modules in
the cDAQ chassis automatically share a single oversample clock to
synchronize data from all sigma-delta modules.
This clock is used as the AI Sample Clock Timebase. While most modules
supply a common oversample clock frequency (12.8 MHz), some modules,
such as the NI 9234, supply a different frequency. When sigma-delta
modules with different oversample clock frequencies are used in an analog
input task, the AI Sample Clock Timebase can use any of the available
frequencies; by default, the fastest available is used. The sampling
rate of all modules in the system is an integer divisor of the frequency
of the AI Sample Clock Timebase.
When one or more sigma-delta modules are in an analog input task, the
sigma-delta modules also provide the signal used as the AI Sample Clock.
This signal is used to cause A/D conversion for other modules in the
system, just as the AI Sample Clock does when a sigma-delta module is not
being used.
When sigma-delta modules are in an AI task, the chassis automatically
issues a synchronization pulse to each sigma-delta modules that resets their
ADCs at the same time. Both the synchronization pulse and the oversample
clock can be routed from or to any PFI line to allow synchronization
between multiple chassis. Because of the filtering used in sigma-delta A/D
converters, these modules usually exhibit a fixed input delay relative to
non-sigma-delta modules in the system. This input delay is specified in the
C Series I/O module documentation.
NI cDAQ-9172 User Guide and Specifications 26 ni.com
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