National Instruments NI 5911 User Manual 2

Computer-Based
Instruments

NI 5911 User Manual

Digital Oscilloscope for PCI

NI 5911 User Manual

October 1998 Edition

Part Number 322150A-01

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© Copyright 1998 National Instruments Corporation. All rights reserved.

Important Information

Warranty

The NI 5911 is warranted against defects in materials and workmanship for a period of one year from the date of
shipment, as evidenced by receipts or other documentation. National Instruments will, at its option, repair or replace
equipment that proves to be defect ive du ring t he wa rranty period . Th is warranty incl udes parts a nd l abor.

The media on which you receive National Instruments software are warranted not to fail to execute programming
instructions, due to defects in materials and workm anship, f or a period of 90 days fr om date of ship ment, as evid enced
by receipts or other documentation. National Instruments will, at its option, repair or replace software media that do
not execute programming instructions if National Instruments receives notice of such defects during the warranty
period. National Instruments does not warrant that the operation of the software shall be uninterrupted or error free.

A Return Material Authorization (RMA) number must be obtained from the factory and clearly marked on the outside
of the package before any equipment will be accepted for warranty work. National Instruments will pay the shipping
costs of returning to the owne r parts whic h are cover ed by warran ty.

National Instruments believes that the information in this manual is accurate. The document has been carefully
reviewed for technical accuracy. In the event that technical or typographical errors exist, National Instruments reserves
the right to make changes to subsequent editions of this document without prior notice to holders of this edition. The
reader should consult National Instruments if errors are suspected. In no event shall National Instrum ents be liable for
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Conventions

The following conventions are used in this manual:

»

!

bold

bold italic

italic

The » symbol leads you through nested menu items and dialog box options
to a final action. The sequence

Fonts

directs you to pull down the

Options

select
last dialog box.

This icon to the left of bold italicized text denotes a note, which alerts you
to important information.

This icon to the left of bold italicized text denotes a caution, which advises
you of precautions to take to avoid injury, data loss, or a system crash.

This icon to the left of bold italicized text denotes a warning, which advises
you of precautions to take to avoid being electrically shocked.

Bold text denotes the names of menus, menu items, parameters, dialog
boxes, dialog box buttons or options, icons, windows, Windows 95 tabs,
or LEDs.

Bold italic text denotes a note, caution, or warning.
Italic text denotes variables, emphasis, a cross reference, or an introduction

to a key concept. This font also denotes text from which you supply the
appropriate word or value, as in Windows 3.x.

, and finally select the

File»Page Setup»Options»Substitute

File

menu, select the

Substitute Fonts

Page Setup

options from the

item,

Contents

Chapter 1
Taking Measurements with the NI 5911

Connecting Signals ........................................................................................................1-1

Introduction to the VirtualBench-Scope Soft Front Panel.............................................1-2

Soft Front Panel Features ................................................................................1-3

Using the VirtualBench-SCOPE Soft Front Panel ........................................................1-5

Acquiring Data ................................................................................................1-5

Chapter 2
Hardware Overview

Measurement Fundamentals ............... ...........................................................................2-2

Differential Input.............................................................................................2-2

Grounding Considerations ................................................................2-2

Input Ranges ................................... ..................................................2-3

Input Impedance............................................... .................................2-3

Input Bias..........................................................................................2-4

Input Protection.................................................................................2-4

AC Coupling....................................................................................................2-4

Measurement Modes.................................... ..................................................................2-4

Oscilloscope Mode..........................................................................................2-5

Flexible Resolution Mode ...............................................................................2-5

Acquisition System........................................................................................................ 2-6

Calibration.......................................................................................................2-7

Internal Calibration...........................................................................2-7

External Calibration..........................................................................2-8

Triggering and Arming....................................................................................2-8

Analog Trigger Circuit......................................................................2-9

Trigger Hold-Off...............................................................................2-11

Memory ...........................................................................................................2-12

Multiple Record...............................................................................................2-13

Errors During Acquisition...............................................................................2-13

RTSI Bus Trigger and Clock Lines.................................................................2-14

PFI Lines .............................. ...........................................................................2-14

PFI Lines as Inputs............................................................................2-14

PFI Lines as Outputs.........................................................................2-14

Synchronization...............................................................................................2-15

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National Instruments Corporation v NI 5911 User Manual

Contents

Appendix A
Specifications

Appendix B
Digitizer Basics

Appendix C
Customer Communication

Glossary

Index

Figures

Figure 1-1. NI 5911 Connectors.............................................................................. 1-2

Figure 1-2. VirtualBench-Scope Soft Front Panel...................................................1-3

Figure 1-3. Acquire Tab of VirtualBench-Scope Settings Dialog Box................... 1-6

Figure 2-1. NI 5911 Block Diagram........................................................................ 2-1

Figure 2-2. Noise-Free Measurements of Signal.....................................................2-2

Figure 2-3. Trigger Sources.....................................................................................2-9

Figure 2-4. Below-Level Analog Triggering Mode ................................................2-10

Figure 2-5. Above-Level Analog Triggering Mode................................................2-10

Figure 2-6. High-Hysteresis Analog Triggering Mode ...........................................2-11

Figure 2-7. Low-Hysteresis Analog Triggering Mode................................ ............2-11

Figure 2-8. Timing with Hold-Off Enabled.............................................................2-12

Figure 2-9. Multiple Buffer Acquisition..................................................................2-13

Figure B-1. Sine Wave Demonstrating the Nyquist Frequency...............................B-1

Figure B-2. Analog Bandwidth ................................................................................B-2

Figure B-3. 1 MHz Sine Wave Sample....................................................................B-3

Figure B-4. Transfer Function of a 3-Bit ADC........................................................B-3

Figure B-5. Dynamic Range of an 8-Bit ADC with Three Different Gain Settings B-5

Figure B-6. Difficult Pulse Train Signal..................................................................B-6

Tables

Table 2-1. Input Ranges for the NI 5911................................................................2-3

Table 2-2. Available Sampling Rates and Corresponding Bandwidth in

Flexible Resolution Mode.....................................................................2-6

NI 5911 User Manual vi

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National Instruments Corporation

Taking Measurements with
the NI 5911

Thank you for buying a National Instruments 5911 digital oscilloscope

with flexible resolution. The NI 5911 offers unsurpassed flexibility for

performing measurements from DC to 100 MHz. Using the NI 5911

flexible resolution feature, you can choose the sampling rate and resolution

best suited to your application.

Detailed specifications for the NI 5911 are in Appendix A, Specifications.

Connecting Signals

Figure 1-1 shows the front panel for the NI 5911. The front panel contains

three connectors—a BNC connector, an SMB connector, and a 9-pin mini

circular DIN connector.

The BNC connector is for attaching the analog input signal you wish to

measure. The BNC connector is analog input channel 0. The SMB

connector is for external triggers and for generating a probe compensation

signal. The SMB connector is PFI1. The DIN connector gives you access

to an additional external trigger line. The DIN connector can be used to

access PFI2.

1

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National Instruments Corporation 1-1 NI 5911 User Manual

Chapter 1 Taking Measurements with the NI 5911

CH0

PFI1

PFI2

(DIN)

Figure 1-1. NI 5911 Connectors

Introduction to the VirtualBench-Scope Soft Front Panel

The VirtualBench-Scope soft front panel allows you to interactively
control your NI 5911 as you would a desktop oscilloscope.

The following sections explain how to make connections to your NI 5911
and take simple measurements using the VirtualBench-Scope soft front
panel, as shown in Figure 1-2. To laun ch the soft front panel, select
Start»Programs» National Instruments Scope»VirtualBench-Scope.

NI 5911 User Manual 1-2

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National Instruments Corporation

Chapter 1 Taking Measurements with the NI 5911

1
2

8

3

4

7
6

1 Channel Display Selector
2 Channel Settings Selector
3 Channel Settings

Soft Front Panel Features

The VirtualBench-Scope soft front panel has the following features:

• Channel Display Selector—selects a waveform for display on the

graphics display.

• Channel Set tings

– Channel Settings Selector—selects the channel whose settings

– Volts/div—adjusts the vertical sensitivity of the channel you

– V. Position—controls the DC offset of the displayed waveform.

• Timebase—controls the timebase setting. Turning the knob

clockwise reduces the time period that appears in the graphics
display. Each horizontal division represents one time period.

• Graphics Display—displays waveforms.

4 Trigger Setting Group
5 Vertical Slider
6 Main Control Bar

Figure 1-2. VirtualBench-Scope Soft Front Panel

will be modified.

select.

7 Zoom Controls
8 Graphics Display

5

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Chapter 1 Taking Measurements with the NI 5911

• Vertical Slider—adjusts the voltage offset for each channel. Use

this slider when you want to adjust multiple waveforms in the
graphics display.

• Trigger Settings Group—controls the conditions required for

signal acquisition; for example, whether to wait for a digital trigger
before acquiring data or whether to acquire data in free-run mode
(no triggering).

• Main Control Bar Buttons

– Run—acquires data continuously. Deselecting this button

places the VirtualBench-Scope in idle mode.

– Single —instructs VirtualBench-Scope to perform a

single-sweep acquisition.

– Auto Setup—configures the scope for the best timebase, volts

per division, and trigger setting for each channel currently
selected with the channel selector.

– Mode —sets the mode of the scope to either volts versus time

or X versus Y mode.

• Zoom Controls—adjusts the view of your display data.
– Scroll Bar—adjusts the zoom view.
– Zoom In—zooms in on displayed data. Each zoom increases

the view by a factor of two.

– Zoom Out—zooms out to full X scale.

Note: Refer to the VirtualBench-Scope Online Help for additional help on the

front panel items.

NI 5911 User Manual 1-4

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National Instruments Corporation

Chapter 1 Taking Measurements with the NI 5911

Using the VirtualBench-SCOPE Soft Front Panel

The following sections describe how to perform simple analog input
measurements using the VirtualBench-SCOPE soft front panel.

Acquiring Data

When you launch VirtualBench-Scope, it operates in continuous run
mode. You can start acquiring signals with VirtualBench-Scope by
completing the following steps:

1. Connect a signal to Channel 0 of your NI 5911.

2. Configure VirtualBench-Scope.

a. Select General Settings from the Edit menu on the front panel.
b. Your NI 5911 is an IVI compliant device. To configure

VirtualBench-SCOPE to use your NI 5911, click on the IVI
Device Type Selector icon located in the Settings dialog box,
shown in Figure 1-3.

c. Select N I 5911 as the device you want to use from the Device

List located in the Settings dialog box, shown in Figure 1-3. If
the NI 5911 does not appear in the Device list, make sure you
have properly configured the device using t he Measurement &
Automation Explorer.

d. Click on OK to use these settings.

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National Instruments Corporation 1-5 NI 5911 User Manual

Chapter 1 Taking Measurements with the NI 5911

Device Type

Selector

Device List

Figure 1-3. Acquire Tab of VirtualBench-Scope Settings Dialog Box

Note:

When you launch VirtualBench-Scope, it automatically uses the settings of
your previous VirtualBench-Scope session.

3. Enable the Ch 0 button in the Channel Selector group. Disable all
other channels.

4. Click on AutoSetup on the main control bar.

5. Click on Run to start the acquisition.

Note: Refer to the VirtualBench-Scope Online Help for additional help on

configuring VirtualBench-Scope for your specific application.

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National Instruments Corporation

Hardware Overview

This chapter includes an overview of the NI 5911, explains the operation of
each functional unit making up your NI 5911, and describes the signal
connections. Figure 2-1 shows a block diagram of the NI 5911.

2

Analog Input

Connector

1 kOhm

Digital IO

Connector

Calibration

Generator

Protect/

Calibration

Mux

AC/DC Coupling

1 MOhm

PGA

Digital Signal

Processor

Figure 2-1.

Noise

Shaper

Timing IO/

Memory Control

Capture

Memory

NI 5911 Block Diagram

A/D Converter
100 MHz, 8-bit

Reference
Clock

Data

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National Instruments Corporation 2-1 NI 5911 User Manual

Chapter 2 Hardware Overview

Measurement Fundamentals

The NI 5911 has a differential programmable gain input amplifier (PGIA)
at the analog input. The purpose of the PGIA is to accurately interface to
and scale the signal presented at the connector to the analog-to-digital
converter (ADC) regardless of source impedance, source amplitude, DC
biasing or common-mode noise voltages.

Differential Input

When measuring high dynamic range signals, ground noise is often a
problem. The PGIA of the NI 5911 allows you to make noise-free
measurements of the signal. The NI 5911 PGIA is a differential amplifier.
The PGIA differential amplifier efficiently rejects any noise which may be
present on the ground signal. Internal to the PGIA, the signal presented at
the negative input is subtracted from the signal presented at the positive
input. As shown in Figure 2-2, this subtraction removes ground noise from
the signal. The inner conductor of the BNC is V+, the outer shell is V–.

Input Signal

Ground Noise

Figure 2-2.

Grounding Considerations

The path for the positive signal has been optimized for speed and linearity.
You should always apply signals to the positive input and ground to the
negative input. Reversing the inputs will result in higher distortion and
lower bandwidth.

The negative input of the amplifier is grounded to PC ground through a
10 kΩ resistor. The PGIA is therefore referenced to ground, so it is not
necessary to make any external ground connections. If the device you
connect to the NI 5911 is already connected to ground, ground-loop noise
voltages may be induced into your system. Note that in most of these
situations, the 10 kΩ resistance to PC ground is normally much higher than

NI 5911 User Manual 2-2

V+

V–

Noise-Free Measurements of Signal

+

–

V

out

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National Instruments Corporation

Chapter 2 Hardware Overview

the cable impedances you use. As a result, most of the noise voltage occurs
at the negative input of the PGIA where it is rejected, rather than in the
positive input, where it would be amplified.

Input Ranges

To optimize the ADC resolution, you can select different gains for the
PGIA. In this way, you can scale your input signal to match the full input
range of the converter. The NI 5911 PGIA offers seven different input
ranges, from ±0.1 V inputs to ±10 V inputs as shown in Table 2-1.

Table 2-1.

Input Ranges for the NI 5911

Range Input Protection Threshold

± 10 V ±10 V

± 5 V ±5 V
± 2 V ±5 V

± 1 V ±5 V
± 0.5 V ±5 V
± 0.2 V ±5 V
± 0.1 V ±5 V

Input Impedance

The input impedance of the NI 5911 PGIA is 1 MΩ between the positive
and negative input. The output impedance of the device connected to the
NI 5911 and the input impedance of the NI 5911 form an impedance
divider, which attenuates the input signal according to the following
formula:

VsR

in

------------------- -=

V

m

RsRin+

where V
external source, and R

is the measured voltage, Vs is the source voltage, Rs is the

m

is the input impedance.

in

If the device you are measuring has a very large output impedance, your
measurements will be affected by this impedance divider. For example, if
the device has 1MΩ output impedance, your measured signal will be 1/2
the actual signal value.

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Chapter 2 Hardware Overview

Input Bias

The inputs of the PGIA typically draw an input bias current of 1 nA at
25° C. Attaching a device with a very high source impedance can cause an
offset voltage to be added to the signal you measure, according to the
formula R
example, if the device you have attached to the NI 5911 has an output
impedance of 10 kΩ, typically the offset voltage is 10 µV (10 kΩ x 1 nA).

× 1 nA, where Rs is the external source impedance. For

s

Input Protection

The NI 5911 features input-protection circuits that protect both the positive
and negative analog input from damage from AC and DC signals up to
±42V.

If the voltage at one of these inputs exceeds a threshold voltage, V
input clamps to V
minimize input currents to a nonharmful level.

The protection voltage, V
Table 2-1.

AC Coupling

When you need to measure a small AC signal on top of a large DC
component, you can use AC coupling. AC coupling rejects any DC
component in your signal before it enters into the PGIA. Activating AC
coupling inserts a capacitor in series with the input impedance. Input
coupling can be selected via software. See Appendix B, Digitizer Basics,
for more information on input coupling.

Measurement Modes

The ADC samples at a constant rate of 100 MS/s with a vertical resolution
of 8 bits. Using random interleaved sampling (RIS), the sample rate can be
increased to 1 GS/s. In this conventional mode of operation called
oscilloscope mode, the analog bandwidth is 100 MHz.

For sampling signals with lower bandwidth, the ADC can be sourced
through a noise shaping circuit that moves quantization noise on the output
of the ADC from lower frequencies to higher frequencies. A digital lowpass
filter applied to the data removes all but a fraction of the original shaped
quantization noise. The signal is then resampled to a lower sampling
frequency and a higher resolution. This mode, called flexible resolution
mode, provides antialiasing protection due to the digital lowpass filter.

and a resistance of 100 kΩ is inserted in the path to

tr

is input range dependent, as shown in

tr,

tr

, the

NI 5911 User Manual 2-4

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National Instruments Corporation

Oscilloscope Mode

In the oscilloscope mode, the NI 5911 works as a conventional desktop
oscilloscope. This mode is useful for displaying waveforms and for
deriving waveform parameters such as slew rate, rise time, and settling
time. The sample resolution in oscilloscope mode is 8 bits.

The ADC converts at a constant rate of 100 MS/s, but you can choose to
store only a fraction of these samples into memory at a lower rate. This
allows you to store waveforms using fewer data points and decreases the
burden of storing, analyzing, and displaying the waveforms. If you need
faster sampling rates, you can use RIS to effectiv ely increase the sampling
rate to 1 GS/s for repetitive waveforms.

In oscilloscope mode, all signals up to 100 MHz are passed to the ADC.
You need to ensure that your signal is band-limited to prevent aliasing.
Aliasing and other sampling terms are described more thoroughly in
Appendix B, Digitizer Basics.

Flexible Resolution Mode

Flexible resolution mode differs from oscilloscope mode in two ways: it
has higher resolution (sampling rate dependent) and the signal bandwidth
is limited to provide antialiasing protection. This mode is useful for spectral
analysis, distortion analysis and other measurements where high resolution
is crucial. Table 2-2 shows the relationship between the available sampling
rates and the corresponding bandwidth for flex ible resolution mode.

Chapter 2 Hardware Overview

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National Instruments Corporation 2-5 NI 5911 User Manual

Chapter 2 Hardware Overview

Table 2-2.

Available Sampling Rates and Corresponding Bandwidth in

Flexible Resolution Mode

Sampling Rate Resolution Bandwidth

12.5 MS/s 12 bits 4 MHz
5 MS/s 14 bits 2 MHz

2.5 MS/s 16 bits 800 kHz
1 MS/s 18 bits 400 kHz
500 MS/s 18 bits 200 kHz
200 MS/s 19 bits 80 kHz
100 MS/s 19 bits 40 kHz
50 MS/s 20 bits 20 kHz
20 MS/s 20 bits 8 kHz
10 MS/s 21 bits 4 kHz

Like any other type of converter that uses noise shaping to enhance
resolution, the frequency response of the converter is only flat to its
maximum useful bandwidth. The NI 5911 has a bandwidth of 4 MHz.
Beyond this frequency , there is a span where the conv erter acts resonant and
where a signal is amplified before being converted. These signals are
attenuated in the subsequent digital filter to prevent aliasing. However, if
the applied signal contains major signal components in this frequency
range, such as harmonics or noise, the converter may overload and signal
data will be invalid. In this case, you will receive an error signaling
overload. You then need to either select a higher input range or attenuate
the signal.

Acquisition System

The NI 5911 acquisition system controls the way samples are acquired and
stored. It is possible for the NI 5911 to acquire data at different rates and
resolutions. There are two sampling methods available in oscilloscope
mode, Real Time and Repetitive (RIS). Using Real Time sampling, you can
acquire data at a rate of 100 MS/n where n is a number from 1 to 4.3
million. RIS sampling can be used on repetitive signals to effectively
extend the sampling rate above 100 MS/s. In RIS mode, you can sample at
rates of 100 MS/s * n where n is a number from 2 to 10. The available

NI 5911 User Manual 2-6

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National Instruments Corporation

Calibration

Chapter 2 Hardware Overview

sampling rates, resolutions, and bandwidth for flexible resolution mode are
shown in Table 2-2.

During the acquisition, samples are stored in a circular buffer that is
continually rewritten until a trigger is received. After the trigger is
received, the NI 5911 continues to acquire posttrigger samples if you have
specified a posttrigger sample count. The acquired samples are placed into
onboard memory. The number of posttrigger or pretrigger samples is only
limited by the amount of onboard memory.

The NI 5911 can be calibrated for very high accuracy and resolution due to
an advanced calibration scheme. There are two different calibration
schemes depending on the type of calibration to be performed. Internal
calibration, the more common of the two schemes, is performed via a
software command that compensates for drifts caused by environmental
temperature changes. Internal calibration can be executed without any
external equipment connected. External calibration, which is performed
much less frequently, is used to recalibrate the board when the specified
calibration interval has expired. External calibration requires you to
connect an external precision voltage reference to the board.

Internal Calibration

To provide the maximum accuracy independent of temperature changes,
the NI 5911 contains a heater that stabilizes the temperature of the most
sensitive circuitries on the board. However, the heater can accommodate
for temperature changes over a fixed range of ±5 °C. When temperatures
exceed this range, the heater will no longer be able to stabilize the
temperature and signal data will no longer be accurate. When the
temperature range has been exceeded, you will receive a warning and you
will need to perform an internal calibration.

By executing a software command, you can internally calibrate the
NI 5911without connecting any external equipment.

Internal calibration performs the following operations:

1. The heater is set to regulate over a range of temperatures centered at
the current environmental temperature. The circuit components require
a certain amount of time to stabilize at the new temperature. This
temperature stabilization accounts for the majority of the calibration
time.

2. Gain and offset are calibrated for each individual input range.

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National Instruments Corporation 2-7 NI 5911 User Manual

Chapter 2 Hardware Overview

3. The linearity of the ADC is calibrated using an internal sinewave
generator as reference.

4. The time-to-digital converter used for RIS measurements is calibrated.

Note Do not apply high-amplitude or high-frequency signals to the NI 5911 during

internal calibration. For optimal calibration performance, disconnect the input
signal from the NI 5911.

External Calibration

External calibration is used to calibrate the internal reference on the
NI 5911. The NI 5911 is already calibrated when it is shipped from the
factory. Periodically, the NI 5911 will need external calibration to remain
within the specified accuracy. For more information on calibration, contact
National Instruments using the support information in Appendix C,

Customer Communication. For actual intervals and accuracy, refer to

Appendix A, Specifications.

Triggering and Arming

There are several triggering methods for the NI 5911. The trigger can be
an analog level that is compared to the input or any of several digital inputs.
You can also call a software function to trigger the board. Figure 2-3 shows
the different trigger sources. When a digital signal is used, that signal must
be at a high TTL level for at least 40 ns before any triggers will be accepted.

NI 5911 User Manual 2-8

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National Instruments Corporation

Chapter 2 Hardware Overview

Analog

Input

Gain

RTSI <0..6>

PFI1, PFI2

High

Level

Low

Level

a. Analog Trigger Circuit

Software

ATC_OUT

b. Trigger and Arm Sources

+

COMP

COMP

–

7

2

Analog

Trigger

Circuit

Trigger

Arm

ATC_OUT

Figure 2-3. Trigger Sources

Analog Trigger Circuit

The analog trigger on the NI 5911 operates by comparing the current
analog input to an onboard threshold voltage. This threshold voltage,
triggerValue, can be set within the current input range in 170 steps. This
means that for a ±10 V input range, the trigger can be set in increments of
20 V/170 = 118 mV . There may also be a hysteresisValue associated with
the trigger that can be set in the same size increments. The hysteresisValue
is used to create a trigger window the signal must pass through before the
trigger is accepted. Triggers can be generated on a rising or falling edge
condition as illustrated in the following figures. The four different modes
of operation for the analog trigger are shown in Figures 2-4 to 2-7.

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National Instruments Corporation 2-9 NI 5911 User Manual

Chapter 2 Hardware Overview

Trigger Value

Falling Edge Trigger

Rising Edge Trigger

Figure 2-4. Below-Level Analog Triggering Mode

In below-level analog triggering mode, the trigger is generated when the
signal value is less than triggerValue. hysteresisValue is unused.

Trigger Value

Falling Edge Trigger

Rising Edge Trigger

Figure 2-5. Above-Level Analog Triggering Mode

In above-level analog triggering mode, the trigger is generated when the
signal value is greater than triggerValue. hysteresisValue is unused.

NI 5911 User Manual 2-10

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National Instruments Corporation

Chapter 2 Hardware Overview

Trigger

Value

Hysteresis

Value

Trigger

Falling Edge Trigger

Rising Edge Trigger

Figure 2-6. High-Hysteresis Analog Triggering Mode

In high-hysteresis analog triggering mode, the trigger is generated when the
signal value is greater than triggerValue, with the hysteresis specified by
hysteresisValue. The signal must cross back below the hysteresisValue
before another trigger is generated.

Hysteresis

Value

Trigger

Value

Trigger

Falling Edge Trigger

Rising Edge Trigger

Figure 2-7. Low-Hysteresis Analog Triggering Mode

In low-hysteresis analog triggering mode, the trigger is generated when the
signal value is less than triggerValue, with the hysteresis specified by
hysteresisValue. The signal must cross back above the hysteresisValue
before another trigger is generated.

Trigger Hold-Off

Trigger hold-off is provided in hardware using a 32-bit counter clocked by
a 25 MHz internal timebase. With this configuration, you can select a
hardware hold-off value of 40 ns to 171.8 s in increments of 40 ns.

©

National Instruments Corporation 2-11 NI 5911 User Manual

Chapter 2 Hardware Overview

Trigger

Hold-Off

Acquisition

In Progress

When a trigger is received during acquisition, the trigger counter is loaded
with the desired hold-off time. Hardware then rejects all triggers until the
counter has expired or the current acquisition completes, whichever is
longer. The time the acquisition takes to complete from the time a trigger
occurs is (posttrigger samples) / (sample rate(MHz)). If this time is larger
than the trigger hold-off time, the trigger hold-off has no effect because
triggers are always rejected during acquisition. Figure 2-8 shows a timing
diagram of signals when hold-off is enabled and the hold-off time is longer
than posttriggered acquisition.

Posttrigger

Pretrigger

Data

Data

Hold-Off Time in nanoseconds

(Adjustable between 40 ns and 171.8 s)

= Trigger Not Accepted
= Trigger Accepted

Figure 2-8. Timing with Hold-Off Enabled

Memory

Samples are acquired into onboard memory on the NI 5911 before being
transferred to the host computer. The minimum size for a buffer is
approximately 4,000 8-bit oscilloscope mode samples or 1,000 32-bit
decimation mode samples. Software allows you to specify buffers of less
than these minimum sizes. When specifying a smaller buffer size, the
minimum number of points are still acquired into onboard memory, but
only the specified number of points are retrieved into the host computer’s
memory.

The total number of samples that can be stored depends on the size of the
Acquisition Memory Module installed on the NI 5911 and on the size of
each acquired sample.

NI 5911 User Manual 2-12

©

National Instruments Corporation

Multiple Record

Chapter 2 Hardware Overview

After the trigger has been received and the posttrigger samples have been
stored, the NI 5911 can be configured to begin another acquisition that is
stored in another memory record on the board. This is a multiple record
acquisition. To perform multiple record acquisitions, the NI 5911 is
configured to the number of records to be acquired before starting the
acquisition. The NI 5911 acquires an additional record each time a trigger
is accepted until all the requested records have been stored in memory.
This process does not require software intervention after the initial setup
has been completed.

Between each record, there is a dead time of approximately 5 µs during
which the trigger is not accepted. During this time, the memory controller
is setting up for the next record. There may also be additional dead time
while the minimum number of pretrigger samples are being acquired.
Figure 2-9 shows a timing diagram of a multiple record acquisition.

Trigger

Acquisition

In Progress

Buffer

123

= Trigger Not Accepted (Pretrigger Points Not Acquired)

1

= Trigger Not Accepted (5 µs Dead Time)

2

= Trigger Not Accepted (Acquisition in Progress)

3

= Trigger Accepted

Errors During Acquisition

The NI 5911 has circuitry to detect error conditions that may affect the
acquired data. The NI 5911 uses a heater circuit to maintain constant
temperature on the critical circuitry used in flexible resolution mode. If
this circuit is unable to maintain the temperature within specification, an
error is generated. This error indicates that the temperature of the ADC is
out of range and should be recalibrated by performing an internal
calibration. During acquisition in flexible resolution mode, an error will be
generated if the input to the ADC goes out of range for the converter. The

5 µS

12

Figure 2-9.

Multiple Buffer Acquisition

©

National Instruments Corporation 2-13 NI 5911 User Manual

Chapter 2 Hardware Overview

fact that this condition has occurred may not be obvious by inspecting the
acquired data due to the digital filtering that takes place on the acquired
data. Therefore an error will occur to let you know that the data includes
some samples that were out of the range of the converter and may be
inaccurate.

RTSI Bus Trigger and Clock Lines

The RTSI bus allows National Instruments boards to synchronize timing
and triggering on multiple devices. The RTSI bus has seven bidirectional
trigger lines and one bidirectional clock signal.

You can program any of the seven trigger lines to provide or accept a
synchronous trigger signal. Y ou can also use any of the RTSI trigger lines
to provide a synchronization pulse from a master board if you are
synchronizing multiple NI 5911 boards.

You can use the RTSI bus clock line to provide or accept a 10 MHz
reference clock to synchronize multiple NI 5911 boards.

PFI Lines

The NI 5911 has two digital lines that can be used to accept a trigger, accept
or generate a reference clock, or output a square wave of programmable
frequency. The function of each PFI line is independent, however, only
one trigger source can be accepted during acquisition.

PFI Lines as Inputs

You can select PFI1 or PFI2 as inputs for a trigger or a reference clock.
Please see the section, Synchronization, for more information about the use
of reference clocks in the NI 5911.

PFI Lines as Outputs

You can select PFI1 or PFI2 to output several digital signals.
Reference Clock is a 10 MHz clock that is synchronous to the 100 MHz

sample clock on the NI 5911. Y ou can use the reference clock to
synchronize to another NI 5911 configured as a slave device or to other
equipment that can accept a 10 MHz reference.

Frequency Output is a 1 kHz digital pulse train signal with a 50% duty
cycle. The most common application of Frequency Output for the NI 5911
is to provide a signal for compensating a passive probe.

NI 5911 User Manual 2-14

©

National Instruments Corporation

Synchronization

Chapter 2 Hardware Overview

The NI 5911 uses a digital phase lock loop to synchronize the 100 MHz
sample clock to a 10 MHz reference. This reference frequency can be
supplied by a crystal oscillator on the board or through an external
frequency input through the RTSI bus clock line or a PFI input.

The NI 5911 may also output its 10 MHz reference on the RTSI bus clock
line or a PFI line so that other NI 5911 boards or other equipment can be
synchronized to the same reference.

While the reference clock input is sufficient to synchronize the 100 MHz
sample clocks, it is also necessary to synchronize clock dividers on each
NI 5911 board so that internal clock divisors are also synchronized on the
different boards. These lower frequencies are important because they are
used to determine trigger times and sample position.

To synchronize the NI 5911 clock dividers, you must connect the boards
with a National Instruments R TSI b us cable. One of the RTSI bus triggers
must be designated as a synchronization line. This line will be an output
from the master board and an input on the slave boards. To synchronize
the boards, a single pulse is sent from the master to the slaves, which gives
them a reference time to clear the clock dividers on the boards. Hardware
arming cannot be used during a multiple board acquisition.

©

National Instruments Corporation 2-15 NI 5911 User Manual

Specifications

This appendix lists the specifications of the NI-5911. These specifications
are typical at 25° C unless otherwise specified.

NI 5911

Acquisition System

Bandwidth..............................................100 MHz maximum, at all input

Number of channels...............................1 for PCI, 2 for VXI

Number of flexible resolution ADC....... 1 for PCI, 2 for VXI

Max sample rate.....................................1 GS/s repetitive, 100 MS/s single

Sample onboard memory....................... 4 MB or 16 MB

A

ranges

shot

Memory sample depth

Sampling

Frequency

100 MHz/n* Oscilloscope 4 MS 16 MS

12.5 MHz Flexible

5 MHz Flexible

2.5 MHz Flexible

1 MHz Flexible

500 kHz Flexible

©

National Instruments Corporation A-1 NI 5911 User Manual

Mode

Resolution

Resolution

Resolution

Resolution

Resolution

Sample depth
(4 MB option)

1 MS 4 MS

1 MS 4 MS

1 MS 4 MS

1 MS 4 MS

1 MS 4 MS

Sample depth

(16 MB option)

Appendix A Specifications

Sampling

Frequency

200 kHz Flexible

100 kHz Flexible

50 kHz Flexible

20 kHz Flexible

10 kHz Flexible

* 1<n<232 in oscilloscope mode

Mode

Resolution

Resolution

Resolution

Resolution

Resolution

Sample depth
(4 MB option)

1 MS 4 MS

1 MS 4 MS

1 MS 4 MS

1 MS 4 MS

1 MS 4 MS

Sample depth

(16 MB option)

Memory record sizes ..............................2,000 samples, to maximum

sample depth determined by
sample frequency

Vertical sensitivity (input ranges)

Noise Referred

Input Range

±10 V 174 dBfs/sqrt(Hz)

to Input

±5 V 168 dBfs/sqrt(Hz)
±2 V 160 dBfs/sqrt(Hz)

±1 V 154 dBfs/sqrt(Hz)
±0.5 V 148 dBfs/sqrt(Hz)
±0.2 V 140 dBfs/sqrt(Hz)
±0.1 V 134 dBfs/sqrt(Hz)

NI 5911 User Manual A-2 © National Instruments Corporation

Acquisition Characteristics

Accuracy

Amplitude accuracy ............................... ± 0.05% signal ± 0.0001% fs

DC offset................................................0.1 mV + 0.01% fs (5° C to 40° C)

Input coupling........................................DC and AC, software selectable

AC coupling cut-off frequency

(–3 dB) ...................................................15 Hz ±2%

Input impedance.....................................1 MΩ ±2%

Max measurable input voltage...............±10 V (DC + peak AC)

Input protection......................................±42 VDC (DC + peak AC)

Appendix A Specifications

(5 to 40° C) for all input ranges at
1 kHz (excluding ripple from
digital filters)

for all input ranges

Input bias current ...................................±1 nA, typical at 25° C

Common-Mode Characteristics

Impedance to chassis ground .................10 kΩ

Common-mode rejection ratio...............CMRR > –70 dB, (Fin < 1 kHz)

©

National Instruments Corporation A-3 NI 5911 User Manual

Appendix A Specifications

Filtering

Sampling

Frequency

100 MHz/n Oscilloscope 100 MHz ±3 dB N/A

12.5 MHz Flexible

5 MHz Flexible

2.5 MHz Flexible

1 MHz Flexible

500 kHz Flexible

200 kHz Flexible

100 kHz Flexible

50 kHz Flexible

20 kHz Flexible

Filter
Mode

Resolution

Resolution

Resolution

Resolution

Resolution

Resolution

Resolution

Resolution

Resolution

Alias

Bandwidth Ripple

3.75 MHz ±0.2 dB –60 dB

2 MHz ±0.1 dB –70 dB

1 MHz ±0.05 dB –80 dB

400 kHz ±0.005 dB –80 dB

200 kHz ±0.005 dB –80 dB

80 kHz ±0.005 dB –80 dB

40 kHz ±0.005 dB –80 dB

20 kHz ±0.005 dB –80 dB

8 kHz ±0.005 dB –80 dB

Attenuation

10 kHz Flexible

Resolution

*1<n<232 in oscilloscope mode

NI 5911 User Manual A-4 © National Instruments Corporation

4 kHz ±0.005 dB –80 dB

Appendix A Specifications

Dynamic Range

Noise (excluding input-referred noise)

Total

Sampling Frequency Bandwidth Noise Density

100 MHz/

12.5 MHz 3.75 MHz –135 dBfs/sqrt(Hz) –64 dBfs
5 MHz 2 MHz –150 dBfs/sqrt(Hz) –83 dBfs

2.5 MHz 1 MHz –155 dBfs/sqrt(Hz) –91 dBfs
1 MHz 400 kHz –160 dBfs/sqrt(Hz) –104 dBfs
500 kHz 200 kHz –160 dBfs/sqrt(Hz) –107 dBfs
200 kHz 80 kHz –160 dBfs/sqrt(Hz) –111 dBfs
100 kHz 40 kHz –160 dBfs/sqrt(Hz) –114 dBfs
50 kHz 20 kHz –160 dBfs/sqrt(Hz) –117 dBfs
20 kHz 8 kHz –160 dBfs/sqrt(Hz) –121 dBfs
10 kHz 4 kHz –160 dBfs/sqrt(Hz) –124 dBfs

n

100 MHz –120 dBfs/sqrt(Hz) –43 dBfs

Noise

*1<n<232 in oscilloscope mode

Distortion

Sampling

Frequency

100 MHz/

12.5 MHz 65 dB 85 dB 125 dB

500 kHz 90 dB 110 dB 150 dB
200 kHz 100 dB 110 dB 160 dB
100 kHz 100 dB 110 dB 160 dB

n

5 MHz 70 dB 90 dB 130 dB
2 MHz 75 dB 95 dB 135 dB
1 MHz 85 dB 105 dB 145 dB

50 kHz 100 dB 110 dB 160 dB
20 kHz 100 dB 110 dB 160 dB
10 kHz 100 dB 110 dB 160 dB

SFDR for input

0 dBfs

50 dB 50 dB N/A

SFDR for input

–20 dBfs

SFDR for input

–60 dBfs (typical)

©

National Instruments Corporation A-5 NI 5911 User Manual

Appendix A Specifications

Timebase System

Number of timebases..............................2, RTSI clock configured as a

10 MHz clock output (Master), or
RTSI clock configured as a
10 MHz reference clock input

(Slave).

Clock accuracy (as Master) ....................10 MHz ± 50 ppm

Clock input tolerance (as Slave).............10 MHz ± 100 ppm

rms,

Clock jitter..............................................<75 pS

reference clock source

Clock compatibility ...............................TTL for both input and output

Interpolator resolution

(repetitive only) ......................................1 ns

Sampling clock frequencies

Oscilloscope mode...........................100 MHz/n, where 1<n<2

Flexible Resolution mode................100 MHz/n, where n = 8, 20, 50,

100, 200, 500, 1000, 2000, 5000,

10000

independent of

32

Synchronization......................................Via RTSI trigger lines

Phase difference......................................Between multiple instruments

<5 ns, at any input frequency

<100 MHz from input connector

to input connector

Triggering Systems

Modes .....................................................Above threshold, below

threshold, between thresholds,

outside thresholds

Source.....................................................CH0, RTSI<0..6>, PFI 1,2

Slope.......................................................Rising/falling

NI 5911 User Manual A-6 © National Instruments Corporation

Appendix A Specifications

Hysteresis...............................................Full-scale voltage/n, where n is

between 1 and 170; full-scale
voltage on TRIG is fixed to ±5 V

(without external attenuation)

Coupling.................................................AC/DC on CH0, TRIG

Pretrigger depth ......................................1 to 16 million samples

Posttrigger depth ....................................1 to 16 million samples

Holdoff by time......................................40 ns - 171.85 in increments of

40 ns

Sensitivity............................................... 170 steps in full-scale voltage

range

TRIG input range...................................± 5 V (without external

attenuation)

TRIG input impedance...........................1 MΩ ± 1% in parallel with 30 pF

± 15 pF

Acquisition Modes

TRIG input protection............................±42 V [(DC + peak AC) < 10 kHz,

without external attenuation]

RIS .........................................................1 GS/s down to 200 MS/s

effective sample rate, repetitive

signals only. Data is interleaved

in software.

RIS accuracy .......................................... <0.5 nS

Single-shot ...................................... .......100 MS/s down to 10 kS/s sample

rate for transient and repetitive

signals

Power Requirements

+5 VDC .................................................4 A

+12 VDC................................................100 mA

–12 VDC ...............................................100 mA

©

National Instruments Corporation A-7 NI 5911 User Manual

Appendix A Specifications

Physical

Dimensions.............................................33.8 x 9.9 cm (13.3 x 3.9 in)

I/O connectors

Analog input CH0............................BNC female

Digital triggers.................................SMB female, 9-pin DIN

Operating Environment

Ambient temperature..............................5 to 40° C

Relative humidity ...................................10% to 90%, noncondensing

Storage Environment

Ambient temperature .............................–20 to 65° C

EMC Compliance

CE97, FCC

Calibration

Internal....................................................Internal calibration is done upon

software command. The
calibration involves gain, offset
and linearity correction for all
input ranges and input modes.

Interval ............................................ week, or any time temperature

changes beyond ±5° C. Hardware
detects temperature variations
beyond calibration limits, which
can also be queried by software.

External...................................................Internal reference requires

recalibration

Interval.............................................3 years

Warm-up time.........................................1 minute

NI 5911 User Manual A-8 © National Instruments Corporation

Digitizer Basics

This appendix explains basic information you need to understand about
making measurements with digitizers, including important terminology.

Understanding Digitizers

T o understand how digitizers work, you should be familiar with the Nyquist
theorem and how it affects analog bandwidth and sample rate. You should
also understand terms including vertical sensitivity, analog-to-digital
converter (ADC) resolution, record length, and triggering options.

Nyquist Theorem

The Nyquist theorem states that a signal must be sampled at least twice as
fast as the bandwidth of the signal to accurately reconstruct the waveform;
otherwise, the high-frequency content will alias at a frequency inside the
spectrum of interest (passband). An alias is a false lower frequency
component that appears in sampled data acquired at too low a sampling
rate. Figure B-1 shows a 5 MHz sine wave digitized by a 6 MS/s ADC. The
dotted line indicates the aliased signal recorded by the ADC at that sample
rate.

B

t

Figure B-1.

The 5 MHz frequency aliases back in the passband, falsely appearing as if
it were a 1 MHz sine wave. To prevent aliasing in the passband, a lo wpass
filter limits the frequency content of the input signal above the Nyquist rate.

©

National Instruments Corporation B-1 NI 5911 User Manual

Sine Wave Demonstrating the Nyquist Frequency

Appendix B Digitizer Basics

Analog Bandwidth

+2 V

Analog bandwidth describes the frequency range (in Hertz) in which a
signal can be digitized accurately. This limitation is determined by the
inherent frequency response of the input path which causes loss of
amplitude and phase information. Analog bandwidth is the frequency at
which the measured amplitude is 3 dB below the actual amplitude of the
signal. This amplitude loss occurs at very low frequencies if the signal is
AC coupled and at very high frequencies regardless of coupling. When the
signal is DC coupled, the bandwidth of the amplifier will extend all the way
to the DC voltage. Figure B-2 illustrates the effect of analog bandwidth on
a high-frequency signal. The result is a loss of high-frequency components
and amplitude in the original signal as the signal passes through the
instrument.

+1 V

0 V
–1 V
–2 V

abc abc

Input Signal

Sample Rate

+1/2 V

Bandwidth

Instrument Measured Signal

Figure B-2.

Analog Bandwidth

0 V
–1/2 V

Sample rate is the rate at which a signal is sampled and digitized by an
ADC. According to the Nyquist theorem, a higher sample rate produces
accurate measurement of higher frequency signals if the analog bandwidth
is wide enough to let the signal to pass through without attenuation. A
higher sample rate also captures more waveform details. Figure B-3
illustrates a 1 MHz sine wave sampled by a 2 MS/s ADC and a 20 MS/s
ADC. The faster ADC digitizes 20 points per cycle of the input signal
compared with 2 points per cycle with the slower ADC. In this example, the
higher sample rate more accurately captures the waveform shape as well as
frequency .

NI 5911 User Manual B-2

©

National Instruments Corporation

Vertical Sensitivity

Appendix B Digitizer Basics

1 µ

= Sample Rate 2 MS/s
= Sample Rate 20 MS/s

Figure B-3. 1 MHz Sine Wave Sample

V ertical sensitivity describes the smallest input v oltage change the digitizer
can capture. This limitation is because one distinct digital voltage
encompasses a range of analog voltages. Therefore, it is possible that a
minute change in voltage at the input is not noticeable at the output of the
ADC. This parameter depends on the input range, gain of the input
amplifier, and ADC resolution. It is specified in volts per LSB. Figure B-4
shows the transfer function of a 3-bit ADC with a vertical range of 5 V
having a vertical sensitivity of 5/8 V/LSB.

111
110

101
100

011
010

001
000

05 V

Range 0-5 V

Voltage Fluctuations

in This Region Will

Be Unnoticed

Figure B-4. Transfer Function of a 3-Bit ADC

©

National Instruments Corporation B-3 NI 5911 User Manual

Appendix B Digitizer Basics

ADC Resolution

Record Length

Triggering Options

ADC resolution limits the accuracy of a measurement. The higher the
resolution (number of bits), the more accurate the measurement. An 8-bit
ADC divides the vertical range of the input amplifier into 256 discrete
levels. W ith a vertical range of 10 V, the 8-bit ADC cannot resolve voltage
differences smaller than 39 mV. In comparison, a 12-bit ADC with 4,096
discrete levels can resolve voltage differences as small as 2.4 mV.

Record length refers to the amount of memory dedicated to storing
digitized samples for postprocessing or display. In a digitizer , record length
limits the maximum duration of a single-shot acquisition. For example,
with a 1,000-sample buffer and a sample rate of 20 MHz, the duration of
acquisition is 50 µs (the number of points multiplied by the acquisition
time/point or 1,000 x 50 ns). With a 100,000-sample buffer and a sample
rate of 20 MHz, the duration of acquisition is 5 ms (100,000 x 50 ns).

One of the biggest challenges of making a measurement is to successfully
trigger the signal acquisition at the point of interest. Since most high-speed
digitizers actually record the signal for a fraction of the total time, they can
easily miss a signal anomaly if the trigger point is set incorrectly. The
NI 5911 is equipped with sophisticated triggering options, such as trigger
thresholds, programmable hysteresis values, and trigger hold-off. The
NI 5911 also has two digital triggers that give you more flexibility in
triggering by allowing you to connect a TTL/CMOS digital signal to trigger
the acquisition.

Making Accurate Measurements

For accurate measurements, you should use the right settings when
acquiring data with your NI 5911. Knowing the characteristics of the
signal in consideration helps you to choose the correct settings. Such
characteristics include:

• Peak-to-peak value—This parameter, in units of volts, reflects the
maximum change in signal voltage. If V is the signal voltage at any
given time, then V
affects the vertical sensitivity or gain of the input amplifier. If you do
not know the peak-to-peak value, start with the smallest gain
(maximum input range) and increase it until the waveform is digitized
using the maximum dynamic range without clipping the signal. Refer

NI 5911 User Manual B-4

pk-to-pk

= V

max

-V

. The peak-to-peak value

min

©

National Instruments Corporation

+127 LSB

0 LSB

–128 LSB

+127 LSB

0 LSB

–128 LSB

to Appendix A, Specifications, for the maximum input voltage for
your NI 5911 device. Figure B-5 shows that a gain of 5 is the best
setting to digitize a 300 mV, 1 MHz sine wave without clipping the
signal.

+7 LSB
–8 LSB

a. Gain = 1, Input Range

+38.4 LSB
–38.4 LSB

b. Gain = 5, Input Range ±1 V, Number of LSBs = 77

±5 V, Number of LSBs = 15

Appendix B Digitizer Basics

+153 LSB

+127 LSB

0 LSB

–128 LSB

–154 LSB

c. Gain = 20, Input Range ±250 mV, Number of LSBs = 307.2

Acquired Signal

Figure B-5. Dynamic Range of an 8-Bit ADC with Three Different Gain Settings

©

National Instruments Corporation B-5 NI 5911 User Manual

Appendix B Digitizer Basics

• Source impedance—Most digitizers and digital storage oscilloscopes

(DSOs) have a 1 MΩ input resistance in the passband. If the source
impedance is large, the signal will be attenuated at the amplifier input
and the measurement will be inaccurate. If the source impedance is
unknown but suspected to be high, change the attenuation ratio on your
probe and acquire data. In addition to the input resistance, all
digitizers, DSOs, and probes present some input capacitance in parallel
with the resistance. This capacitance can interfere with your
measurement in much the same way as the resistance does.

• Input frequency—If your sample rate is less than twice the highest

frequency component at the input, the frequency components above
half your sample rate will alias in the passband at lower frequencies,
indistinguishable from other frequencies in the passband. If the
signal’s highest frequency is unknown, you should start with the
digitizer’s maximum sample rate to prevent aliasing and reduce the
digitizer’s sample rate until the display sho ws either enough c ycles of
the waveform or the information you need.

• General signal shape—Some signals are easy to capture by ordinary

triggering methods. A few iterations on the trigger level finally render
a steady display . This method works for sinusoidal, triangular , square,
and saw tooth waves. Some of the more elusive waveforms, such as
irregular pulse trains, runt pulses, and transients, may be more difficult
to capture. Figure B-6 shows an example of a difficult pulse-train
trigger.

+V

5 V

12 34

Trigger Level

Hold-off Hold-off

1 and 3 = Trigger Accepted

2 and 4 = Trigger Ignored

Figure B-6. Difficult Pulse Train Signal

NI 5911 User Manual B-6

t

©

National Instruments Corporation

Appendix B Digitizer Basics

Ideally, the trigger event should occur at condition one, but sometimes the
instrument may trigger on condition two because the signal crosses the
trigger level. You can solve this problem without using complicated signal
processing techniques by using trigger hold-off, which lets you specify a
time from the trigger event to ignore additional triggers that fall within that
time. With an appropriate hold-off value, the waveform in Figure B-6 can
be properly captured by discarding conditions two and four.

• Input coupling—You can configure the input channels on your
NI 5911 to be DC coupled or AC coupled. DC coupling allows DC and
low-frequency components of a signal to pass through without
attenuation. In contrast, AC coupling removes DC offsets and
attenuates low frequency components of a signal. This feature can be
exploited to zoom in on AC signals with large DC offsets, such as
switching noise on a 12 V power supply. Refer to Appendix A,

Specifications, for input limits that must be observed regardless of

coupling.

©

National Instruments Corporation B-7 NI 5911 User Manual

C

Customer Communication

For your convenience, this appendix contains forms to help you gather the information necessary
to help us solve your technical problems and a form you can use to comment on the product
documentation. When you contact us, we need the information on the Technical Support Form and
the configuration form, if your manual contains one, about your system configuration to answer your
questions as quickly as possible.

National Instruments has technical assistance through electronic, fax, and telephone systems to quickly
provide the information you need. Our electronic services include a bulletin board service, an FTP site,
a fax-on-demand system, and e-mail support. If you have a hardware or software problem, first try the
electronic support systems. If the information available on these systems does not answer your
questions, we offer fax and telephone support through our technical support centers, which are staffed
by applications engineers.

Electronic Services

Bulletin Board Support

National Instruments has BBS and FTP sites dedicated for 24-hour support with a collection of files
and documents to answer most common customer questions. From these sites, you can also download
the latest instrument drivers, updates, and example programs. For recorded instructions on how to use
the bulletin board and FTP services and for BBS automated information, call 512 795 6990. You can
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Up to 14,400 baud, 8 data bits, 1 stop bit, no parity

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Up to 9,600 baud, 8 data bits, 1 stop bit, no parity

France: 01 48 65 15 59

Up to 9,600 baud, 8 data bits, 1 stop bit, no parity

FTP Support

To access our FTP site, log on to our Internet host, ftp.natinst.com, as anonymous and use
your Internet address, such as
documents are located in the

©

National Instruments Corporation C-1 NI 5911 User Manual

[e-mail], as your password. The support files and

/support directories.

Fax-on-Demand Support

Fax-on-Demand is a 24-hour information retrieval system containing a library of documents on a wide
range of technical information. You can access Fax-on-Demand from a touch-tone telephone at
512 418 1111.

E-Mail Support (Currently USA Only)

You can submit technical support questions to the applications engineering team through e-mail at the
Internet address listed below . Remember to include your name, address, and phone number so we can
contact you with solutions and suggestions.

[e-mail]

Telephone and Fax Support

National Instruments has branch offices all over the world. Use the list below to find the technical
support number for your country. If there is no National Instruments office in your country, contact
the source from which you purchased your software to obtain support.

Country Telephone Fax

Australia 03 9879 5166 03 9879 6277
Austria 0662 45 79 90 0 0662 45 79 90 19
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Québec

Canada (
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NI 5911 User Manual C-2

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Technical Support Form

Photocopy this form and update it each time you make changes to your software or hardware, and use
the completed copy of this form as a reference for your current configuration. Completing this form
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Clock speed ______MHz RAM _____MB Display adapter __________________________
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NI 5911 Hardware and Software Configuration Form

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Complete a new copy of this form each time you re vise your softw are or hardw are configuration, and
use this form as a reference for your current configuration. Completing this form accurately before
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Other Products

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Microprocessor ______________________________________ ____________________________
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Title: NI 59 11 User Manual
Edition Date: October 1998
Part Number: 322150A-01

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Glossary

Prefix Meanings Value

p- pico 10
n- nano- 10
µ- micro- 10

m- milli- 10

k- kilo- 10

M- mega- 10

G- giga- 10

Numbers/Symbols

% percent
+ positive of, or plus

–12

–9

–6

–3

3

6

9

– negative of, or minus
/per
°degree
± plus or minus
Ω ohm

A

A amperes
AC alternating current
AC coupled the passing of a signal through a filter network that removes the

DC component of the signal

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National Instruments Corporation G-1 NI 5911 User Manual

Glossary

A/D analog-to-digital
ADC analog-to-digital converter—an electronic device, often an integrated

circuit, that converts an analog voltage to a digital number

ADC resolution the resolution of the ADC, which is measured in bits. An ADC with16 bits

has a higher resolution, and thus a higher degree of accuracy, than a 12-bit
ADC.

amplification a type of signal conditioning that improves accuracy in the resulting

digitized signal and reduces noise

amplitude flatness a measure of how close to constant the gain of a circuit remains over a range

of frequencies

attenuate

to reduce in magnitude

B

b bit—one binary digit, either 0 or 1
B byte—eight related bits of data, an eight-bit binary number. Also used to

denote the amount of memory required to store one byte of data.

bus the group of conductors that interconnect individual circuitry in a computer.

Typically, a bus is the expansion vehicle to which I/O or other devices are
connected. Examples of PC buses are the PCI and ISA bus.

C

C Celsius
CMRR common-mode rejection ratio—a measure of an instrument’s ability to

reject interference from a common-mode signal, usually expressed in
decibels (dB)

coupling the manner in which a signal is connected from one location to another

D

dB decibel—the unit for expressing a logarithmic measure of the ratio of two

signal levels: dB=20log10 V1/V2, for signals in volts

NI 5911 User Manual G-2

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National Instruments Corporation

Glossary

DC direct current
default setting a default parameter value recorded in the driver. In many cases, the default

input of a control is a certain value (often 0) that means use the current
default setting.

differential input an analog input consisting of two terminals, both of which are isolated from

computer ground, whose difference is measured

double insulated a device that contains the necessary insulating structures to provide electric

shock protection without the requirement of a safety ground connection

drivers software that controls a specific hardware instrument

E

EEPROM electrically erasable programmable read-only memory—ROM that can be

erased with an electrical signal and reprogrammed

F

filtering a type of signal conditioning that allows you to filter unwanted signals from

the signal you are trying to measure

G

gain the factor by which a signal is amplified, sometimes expressed in decibels

H

hardware the physical components of a computer system, such as the circuit boards,

plug-in boards, chassis, enclosures, peripherals, cables, and so on
harmonics multiples of the fundamental frequency of a signal
Hz hertz—per second, as in cycles per second or samples per second

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National Instruments Corporation G-3 NI 5911 User Manual

Glossary

I

in. inches
inductance the relationship of induced voltage to current
input bias current the current that flows into the inputs of a circuit
input impedance the measured resistance and capacitance between the input terminals of a

circuit

instrument driver a set of high-level software functions that controls a specific plug-in DAQ

board. Instrument drivers are available in several forms, ranging from a
function callable language to a virtual instrument (VI) in LabVIEW.

interrupt a computer signal indicating that the CPU should suspend its current task

to service a designated activity
interrupt level the relative priority at which a device can interrupt
I/O input/output—the transfer of data to/from a computer system involving

communications channels, operator interface devices, and/or data

acquisition and control interfaces
ISA industry standard architecture

M

m meters.
MB megabytes of memory.

N

noise an undesirable electrical signal—Noise comes from external sources such

as the AC power line, motors, generators, transformers, fluorescent lights,

soldering irons, CR T displays, computers, electrical storms, welders, radio

transmitters, and internal sources such as semiconductors, resistors, and

capacitors. Noise corrupts signals you are trying to send or receive.

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National Instruments Corporation

Glossary

O

Ohm’s Law (R=V /I)—the relationship of voltage to current in a resistance
overrange a segment of the input range of an instrument outside of the normal

measuring range. Measurements can still be made, usually with a
degradation in specifications.

P

PCI Peripheral Component Interconnect—a high-performance expansion bus

architecture originally developed by Intel to replace ISA and EISA; it is
achieving widespread acceptance as a standard for PCs and workstations

and offers a theoretical maximum transfer rate of 132 Mbytes/s
peak value the absolute maximum or minimum amplitude of a signal (AC + DC)
PXI PCI eXtensions for Instrumentation. PXI is an open specification that

builds off the CompactPCI specification by adding

instrumentation-specific features.

R

Rresistor
RAM random-access memory
resolution the smallest signal increment that can be detected by a measurement

system. Resolution can be expressed in bits or in digits. The number of bits

in a system is roughly equal to 3.3 times the number of digits.
rms root mean square—a measure of signal amplitude; the square root of the

average value of the square of the instantaneous signal amplitude
ROM read-only memory

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National Instruments Corporation G-5 NI 5911 User Manual

Glossary

S

s seconds
S samples
sense in four-wire resistance the sense measures the voltage across the resistor

being excited by the excitation current

settling time the amount of time required for a voltage to reach its final value within

specified limits

S/s samples per second—used to express the rate at which an instrument

samples an analog signal

system noise a measure of the amount of noise seen by an analog circuit or an ADC when

the analog inputs are grounded

T

temperature
coefficient

thermal drift measurements that change as the temperature varies
thermal EMFs thermal electromotive forces—voltages generated at the junctions of

thermoelecótric
potentials

transfer rate the rate, measured in bytes/s, at which data is moved from source to

the percentage that a measurement will vary according to temperature. See
also thermal drift

dissimilar metals that are functions of temperature. Also called
thermoelectric potentials.

See thermal EMFs.

destination after software initialization and set up operations; the maximum
rate at which the hardware can operate

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National Instruments Corporation

V

Vvolts
VAC volts alternating current
VDC volts direct current

Glossary

V

error

voltage error
VI virtual instrument—(1) a combination of hardware and/or software

elements, typically used with a PC, that has the functionality of a classic

stand-alone instrument (2) a LabVIEW software module (VI), which

consists of a front panel user interface and a block diagram program
V

rms

volts, root mean square value

W

waveform shape the shape the magnitude of a signal creates over time
working voltage the highest voltage that should be applied to a product in normal use,

normally well under the breakdown voltage for safety margin

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National Instruments Corporation G-7 NI 5911 User Manual

Index

A

AC coupling , 2-4
accuracy characteristics, A-3
acquisition, multiple record, 2-13 to 2-14
acquisition characteristics specifications,

A-3 to A-5

accuracy, A-3
common-mode characteristics, A-3
distortion, A-5
dynamic range, A-5
filtering, A-4

acquisition modes specifications, A-7 to A-8

calibration, A-8
EMC compliance, A-8
operating environment, A-8
power requirements, A-7
storage environment, A-8

acquisition system, 2-6 to 2-16

calibration, 2-7 to 2-8

external calibration, 2-8

internal calibration, 2-7 to 2-8
errors during acquisition, 2-14
memory, 2-12
multiple record, 2-13 to 2-14
PFI lines, 2-15
RTSI bus trigger and clock lines,

2-14 to 2-15
specifications, A-1 to A-2
synchronization, 2-15 to 2-16
triggering and arming, 2-8 to 2-12

above-level analog triggering mode

(figure), 2-10
analog trigger circuit, 2-9 to 2-11
below-level analog triggering mode

(figure), 2-10
high-hysteresis analog triggering mode

(figure), 2-11

low-hysteresis analog triggering mode

(figure), 2-11

trigger hold-off, 2-11 to 2-12

VirtualBench-Scope soft front panel,

1-5 to 1-6
ADC resolution, B-4
analog bandwidth, B-2
analog trigger circuit, 2-9 to 2-11

above-level analog triggering mode

(figure), 2-10

below-level analog triggering mode

(figure), 2-10

high-hysteresis analog triggering mode

(figure), 2-11

low-hysteresis analog triggering mode

(figure), 2-11
arming. See triggering and arming.

B

bias, input, 2-4
block diagram of NI 5911, 2-1
BNC connector, 1-1

location on front panel (figure), 1-2

bulletin board support, C-1

C

calibration

external calibration, 2-8
internal calibration, 2-7 to 2-8

specifications, A-8
clock lines, 2-14 to 2-15
common-mode characteristics, A-3
connectors

BNC connector, 1-1

DIN connector, 1-1

location on front panel (figure), 1-2

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National Instruments Corporation I-1 NI 5911 User Manual

Index

SMB connector, 1-1
conventions used in manual, v
customer communication, C-1 to C-2

D

dead time, in multiple record acquisition, 2-13
differential input, 2-2 to 2-4

grounding considerations, 2-2 to 2-3

input bias, 2-4

input impedance, 2-3 to 2-4

input protection, 2-4

input ranges, 2-3

noise-free signal measurement

(figure), 2-2

digitizers, B-1 to B-7

ADC resolution, B-4

analog bandwidth, B-2

making accurate measurements,

B-4 to B-7

dynamic range of 8-bit ADC

(figure), B-5
general signal shape, B-6 to B-7
input coupling, B-7
input frequency, B-6
peak-to-peak value, B-4 to B-5
source impedance, B-6
trigger hold-off, B-7

Nyquist theorem, B-1
record length, B-4
sample rate, B-2 to B-3
triggering options, B-4
vertical sensitivity, B-3

DIN connector, 1-1

location on front panel (figure), 1-2
distortion specifications, A-5
dynamic range specifications, A-5

E

electronic support services, C-1 to C-2

e-mail support, C-2
EMC compliance, A-8
errors during acquisition, 2-14

F

fax and telephone support numbers, C-2
Fax-on-Demand support, C-2
filtering specifications, A-4
flexible resolution mode, 2-5 to 2-6

available sampling rates (table), 2-6

FTP support, C-1

G

grounding considerations, 2-2 to 2-3

H

hardware overview, 2-1 to 2-16. See also

specifications.

AC coupling, 2-4
acquisition system, 2-6 to 2-16

calibration, 2-7 to 2-8
errors during acquisition, 2-14
memory, 2-12
multiple record, 2-13 to 2-14
PFI lines, 2-15
RTSI bus trigger and clock lines,

2-14 to 2-15
synchronization, 2-15 to 2-16
triggering and arming, 2-8 to 2-12

block diagram of NI 5911, 2-1
differential input, 2-2 to 2-4

grounding considerations, 2-2 to 2-3
input bias, 2-4
input impedance, 2-3 to 2-4
input protection, 2-4
input ranges, 2-3
noise-free signal measurement

(figure), 2-2

NI 5911 User Manual I-2

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National Instruments Corporation

Index

measurement fundamentals, 2-2 to 2-4
measurement modes, 2-4 to 2-6

flexible resolution mode, 2-5 to 2-6
oscilloscope mode, 2-5

hysteresis value. See analog trigger circuit.

I

impedance

formula for impedance divider, 2-3
input and output impedance,

2-3 to 2-4

source impedance, B-6
input bias, 2-4
input coupling, B-7
input frequency, B-6
input impedance, 2-3 to 2-4
input protection circuits, 2-4
input ranges, 2-3

M

measurement fundamentals, 2-2 to 2-4

AC coupling , 2-4
differential input, 2-2 to 2-4

grounding considerations, 2-2 to 2-3

input bias, 2-4

input impedance, 2-3 to 2-4

input protection, 2-4

input ranges, 2-3

noise-free signal measurement

(figure), 2-2

measurement modes, 2-4 to 2-6

flexible resolution mode, 2-5 to 2-6

oscilloscope mode, 2-5
memory size, 2-12
multiple record acquisition, 2-13 to 2-14

dead time, 2-13

multiple buffer acquisition (figure), 2-14

N

NI 5911. See also hardware overview.

block diagram, 2-1
connectors

BNC connector, 1-1
DIN connector, 1-1
location on front panel (figure), 1-2

SMB connector, 1-1
front panel (figure), 1-2
specifications, A-1 to A-8

acquisition characteristics,

A-3 to A-5
acquisition modes, A-7 to A-8
acquisition system, A-1 to A-2
timebase system, A-6
triggering systems, A-6 to A-7

VirtualBench-Scope soft front panel,

1-2 to 1-6

Acquire tab (figure), 1-6
acquiring data, 1-5 to 1-6
features, 1-3 to 1-4
front panel (figure), 1-3

noise-free measurements, 2-2
Nyquist theorem, B-1

O

operating environment specifications, A-8
oscilloscope mode, 2-5
output impedance, 2-3 to 2-4

P

peak-to-peak value, B-4 to B-5
PFI lines

as inputs, 2-15
as outputs, 2-15

PGIA

noise-free measurements, 2-2
removing ground noise (figure), 2-2

physical specifications, A-8

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National Instruments Corporation I-3 NI 5911 User Manual

Index

power requirement specifications, A-7
pulse train signal, difficult (figure), B-6

R

Real Time sampling, 2-6
record length, B-4
Repetitive (RIS) sampling, 2-6
RTSI bus trigger and clock lines

purpose and use, 2-14 to 2-15
synchronization, 2-16

S

sample rate

digitizers, B-2 to B-3
flexible resolution mode sampling rates

(table), 2-6
signal shape, general, 2-6
SMB connector, 1-1

location on front panel (figure), 1-2
source impedance, B-6
specifications, A-1 to A-8

acquisition characteristics, A-3 to A-5

accuracy, A-3
common-mode characteristics, A-3
distortion, A-5
dynamic range, A-5
filtering, A-4

acquisition modes, A-7 to A-8

calibration, A-8
EMC compliance, A-8
operating environment, A-8
physical, A-8
power requirements, A-7

storage environment, A-8
acquisition system, A-1 to A-2
timebase system, A-6
triggering systems, A-6 to A-7

storage environment specifications, A-8
synchronization, 2-15 to 2-16

T

technical support, C-1 to C-2
telephone and fax support numbers, C-2
timebase system specifications, A-6
triggering and arming, 2-8 to 2-12

analog trigger circuit, 2-9 to 2-11

above-level analog triggering mode

(figure), 2-10

below-level analog triggering mode

(figure), 2-10

high-hysteresis analog triggering

mode (figure), 2-11

low-hysteresis analog triggering

mode (figure), 2-11
specifications, A-6 to A-7
timing with hold-off enabled

(figure), 2-12
trigger hold-off, 2-11 to 2-12, B-7
trigger sources (figure), 2-9

triggering options, for digitizers, B-4

V

vertical sensitivity

digitizers, B-3
specifications, A-2

VirtualBench-Scope soft front panel,

1-2 to 1-6

Acquire tab (figure), 1-6
acquiring data, 1-5 to 1-6
features, 1-3 to 1-4
front panel (figure), 1-3

NI 5911 User Manual I-4

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National Instruments Corporation