National Instruments NI cDAQ-9172 User manual

USER GUIDE AND SPECIFICATIONS

NI cDAQ-9172

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 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.

Figure 1. NI cDAQ-9172

1 Power Switch

2 Ready/Active LEDs

3 Power Connector

4 USB Connector

5 Empty Module Slots

6 Installed C Series I/O Modules

7 Screw for Ground Connection

NI cDAQ-9172

Ready

Active

11-30 VDC

15 W

OFF

ON

12345

1

2

3

4 5 6

7

NI cDAQ-9172 User Guide and Specifications 2 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

pk

or

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.

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.

Installing the NI cDAQ-9172

Figure 2 shows the dimensions of the NI cDAQ-9172 chassis.

Figure 2. NI cDAQ-9172 with Dimensions in Millimeters (Inches)

53.8 mm

(2.12 in.)

46.0 mm

(1.81 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.)

24.8 mm

(0.98 in.)

23.2 mm

(0.91 in.)

19.1 mm

(0.75 in.)

31.7 mm

(1.25 in.)

59.6 mm

(2.35 in.)

44.1 mm

(1.74 in.)

63.1 mm

(2.49 in.)

36.4 mm

(1.43 in.)

51.7 mm

(2.04 in.)

165.1 mm

(6.50 in.)

59.6 mm

(2.35 in.)

88.1 mm

(3.50 in.)

254.0 mm

(10.00 in.)

NATIONAL

INSTRUMENTS

NI cDAQ-9172

11-30 VDC

15 W

ON

OFF

Active

8 7 6 5 4 3 2 1

Ready

19.0 mm

(0.75 in.)

4.10 mm

(0.16 in.)

NI cDAQ-9172 User Guide and Specifications 4 ni.com

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

ni.com.

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 50.8 mm (2 in.) of clearance in front of modules for common connector

cabling, such as the 10-terminal detachable screw terminal connector.

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 put on 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.

Figure 3. NI 9901 Desktop Mounting Kit

Mounting the 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 × 16 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 Dimensions and Installation on the NI cDAQ-9172

Mounting the 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 × 16

screws (as pictured in the following diagram). 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 can be used with M4, M5, No. 8, or No.10 panhead

NI cDAQ-9172 User Guide and Specifications 6 ni.com

screws. Figure 5 illustrates the panel dimensions and installation on the NI

cDAQ-9172 chassis. Refer to the documentation included with the NI 9905

shipping kit for more detailed dimensions.

Figure 5. Panel Mount Dimensions and Installation on the NI cDAQ-9172

NATIONAL

INSTRUMENTS

NI cDAQ-9172

11-30 VDC

15 W

ON

OFF

Active

87654321

Ready

330.2 mm

(13.00 in.)

88.1 mm

(3.47 in.)

28.1 mm

(1.11 in.)

48.1 mm

(1.90 in.)

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 NI-DAQmx software,

VI Logger, and the NI-DAQ Device Documentation Browser. 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

ni.com/support. After you install it, the NI-DAQ Device

Documentation Browser is available from Start»Programs»National Instruments»

NI-DAQ»Browse Device Documentation. The DAQ Getting Started Guide is available

after installation from Start»Programs»National Instruments»NI-DAQ»DAQ Getting

Started Guide.

2. If you are not using any mounting accessories, attach the provided

rubber standoffs to the back of the NI cDAQ-9172 chassis.

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

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.

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.

1 Attached to System Ground

1

NI cDAQ-9172 User Guide and Specifications 8 ni.com

5. Remove the plastic cover from the connector in any empty module slot.

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.

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.

NI cDAQ-9172

12. Expand Devices and Interfaces, and then expand NI-DAQmx

Devices.

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

ni.com/support/install for

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

ni.com/support/install

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.

Ready LED

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 1. Active LED

LED Definition

Amber Power is applied, but USB connection is not

established

Green USB traffic present

Off No USB traffic present

Table 2. Ready LED

LED Definition

Amber Hi-Speed (480 Mbit/sec)

NI cDAQ-9172 User Guide and Specifications 10 ni.com

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.

Figure 8. NI cDAQ-9172 Block Diagram

C Series I/0 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

Green Full-Speed (12 Mbit/sec)

Off USB connection is not established

Table 2. Ready LED (Continued)

LED Definition

C Series

I/O Module

C Series

I/O Module

C Series

I/O Module

cDAQ Module

Interface

USB-

STC2

USB

2.0

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. To access this

KnowledgeBase, go to

ni.com/info and enter the info code rdcdaq.

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 or

hardware-timed reads and writes. Correlated Digital I/O modules can

perform the following tasks:

• Used in any slot—software-timed reads and writes.

• Used in slots 1 though 4—Digital Waveform Generation and

Acquisition (Correlated Input/Output)

• Used in slots 5 and 6—Counter/Timer

• Used in slots 5 and 6—Access PFI signals

To determine the capability of digital I/O modules supported by the

NI cDAQ-9172 chassis, refer to the KnowledgeBase document, CSeries

Modules Supported in the NI cDAQ-9172. To access this KnowledgeBase

document, go to

ni.com/info and enter the info code rdcdaq.

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.

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

NI cDAQ-9172 User Guide and Specifications 12 ni.com

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.

PFI Signals

The PFI signals, available through correlated digital input and output

modules installed in slots 5 and 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.

Analog Input

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 may 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 triggering, external

digital, 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

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

NI cDAQ-9172 User Guide and Specifications 14 ni.com

The source also can be one of several other internal signals on your

NI cDAQ-9172 chassis. Refer to Device Routing in MAX 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»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

ni.com/manuals.

You also can specify whether the measurement acquisition begins on the

rising edge or falling edge of ai/StartTrigger.

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 or falling edge of the Analog Comparison Event

signal, depending on the trigger properties.

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.

When the acquisition begins, the NI cDAQ-9172 chassis begins to fill the

buffer. After the specified number of pretrigger samples are captured, the

NI cDAQ-9172 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 discards

it. Refer to the KnowledgeBase document, Can a Pretriggered Acquisition

be Continuous?, for more information. To access this KnowledgeBase,

go to

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.

Figure 9. Reference Trigger Final Buffer

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 Device Routing in MAX 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»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

ni.com/manuals.

You also can specify whether the measurement acquisition stops on the

rising edge or falling edge of ai/ReferenceTrigger.

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.

Reference Trigger

Pretrigger Samples

Complete Buffer

Posttrigger Samples

NI cDAQ-9172 User Guide and Specifications 16 ni.com

Routing AI Reference Trigger Signal to an Output Terminal

You can route ai/ReferenceTrigger to any output PFI terminal.

AI Pause Trigger Signal

The Pause Trigger signal can be generated from internal or external

sources. Any time the signal deasserts, you can use the Pause Trigger signal

to pause the acquisition.

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 Device Routing in MAX 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»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

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 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.

Figure 10. Sample Clock Timing Options

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

Analog Comparison

Event

20 MHz Timebase

100 kHz Timebase

Programmable

Clock

Divider

ai/SampleClock

Timebase

PFI

Analog Comparison Event

Ctr

n

Internal Output

ai/SampleCloc

k

PFI

Sigma-Delta Module Internal Output

NI cDAQ-9172 User Guide and Specifications 18 ni.com

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,

like 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.

Slow Sample Rate Modules

Some C Series analog input modules are specifically designed for

measuring signals that vary slowly, such as temperature. Because of their

slow rate, it is not appropriate for these modules to constrain the AI Sample

Clock to operate at or slower than their maximum rate. When using such a

module in the cDAQ chassis, the maximum Sample Clock rate can run

faster than the maximum rate for the module. When operating at a rate

faster than these slow rate modules can support, the slow rate module

returns the same point repeatedly, until a new conversion completes. The

first point is acquired when the task is committed. The second point is

acquired after the start trigger.

Figure 11. Sample Clock Timing Example

For example, if running an AI task at 1 kHz using a module with a

maximum rate of 10 Hz, the slow module returns 100 samples of the first

point, followed by 100 samples of the second point, etc. Other modules in

the task will return 1,000 new data points per second, which is normal.

When performing a single-point acquisition, no points are repeated.

Refer to the KnowledgeBase document, C Series Modules Supported in the

NI cDAQ-9172, for more information. To access this KnowledgeBase,

go to

ni.com/info and enter the info code rdcdaq.

Getting Started with AI Applications in Software

You can use the NI cDAQ-9172 chassis in the following analog input

applications:

• Single-Point

•Finite

• Continuous

ai/StartTrigger

Data from

A/D Conversion

(Slow Module)

ai/SampleClock

Data Returned

to AI Task

1st A/D Conversion 2nd A/D Conversion 3rd A/D Conversion

A

B C

A A A B B B C

NI cDAQ-9172 User Guide and Specifications 20 ni.com

For more information about programming analog input applications and

triggers in software, Refer to 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»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

ni.com/manuals.

Analog Output

To generate analog output, insert an analog output C Series I/O module in

any slot on the NI cDAQ-9172 chassis. The generation specifications, such

as the number of channels, channel configuration, update rate, and output

range, are determined by the type of C Series I/O module used. For more

information, refer to the documentation included with your C Series I/O

modules.

You can run one hardware-timed (waveform) analog output task at a time

on the NI cDAQ-9172 chassis, with up to 16 waveform channels. At the

same time, you can also run one or more software-timed (single-point or

immediate) tasks.

For each analog output module, you can either:

• Assign all of the channels on the module to the hardware-timed task.

• Assign all of the channels on the module to one or more

software-timed tasks.

On a single AO module, you cannot assign some channels to a

hardware-timed task and other channels (on the same module) to

a software-timed task.

Analog Output Data Generation Methods

When performing an analog output operation, you either can perform

software-timed or hardware-timed generations. Hardware-timed

generations must be buffered.

Software-Timed Generations

With a software-timed generation, software controls the rate at which data

is generated. Software sends a separate command to the hardware to initiate

each DAC conversion. In NI-DAQmx, software-timed generations are

referred to as on-demand timing. Software-timed generations are also

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National Instruments NI cDAQ-9172 User manual

National Instruments NI cDAQ-9172 User manual

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