Keysight Technologies Transitioning to a PXI Test System

Keysight Technologies Transitioning to a PXI Test System
Keysight Technologies
Transitioning to a PXI Test System
Application Note
02 | Keysight | Transitioning to a PXI Test System - Application Note
Transitioning to a PXI Test System
PXI System Infrastructure
Transitioning from benchtop test instruments to a PXI, or AXIe for
a smaller, more powerful test system, is a big step. Figuring out
where to start can be overwhelming especially with the demands
to quickly get test systems set up and running. As you begin the
process of selecting PXI hardware and software, you should be
aware of the options and tradeoffs that will affect how quickly the
test system is set up, the complexity of software programming,
optimization for fast throughput, the types of measurements
and analysis and more. These trade-offs will affect your system
development strategy including selection of instruments,
software tools, and the software programming environment.
Selecting instruments and developing a software strategy that
supports today’s test needs as well as the futures’ can save
engineering time and cost.
PXI test system development starts with selecting a PXIe chassis
which includes the PCIe® bus and provides a true performance
advantage. Next, to control the test system, you will select a
remote personal computer (PC) or an embedded PXIe controller.
Remote PCs are nice for PXI test systems that are located in an
area away from the test system. A PC also offers more options
for configuration flexibility, raw computing power, and additional
interconnects at a lower price than an embedded controller.
A remote PC can be connected to the PXIe chassis through a
host PC adapter card installed in the computer, and a cable
connection from the host adapter to a PCI interface card in the
chassis. Chassis interface cards are available with Gen1, Gen2,
and Gen3 capability with the Gen3 cards offering the best
performance. The test system speed will be determined by the
slowest device. So, if you need the best performance ensure that
all the components are Gen 3 capable. Also, look for PXIe vendors
that provide details on supported PCs to ensure that the PC you
use will operate with the PXIe test system as expected. (See
Keysight’s list of Tested PCs literature number 5990-7632EN.)
Having a good understanding of your options and the pros and
cons upfront will help you succeed as you develop a new PXI
test system or update your existing test system with PXI or AXIe
instruments. While some of the information applies to AXIe
system, this paper focuses on hardware and software selection
and the start-up process of a PXI test system. The key test
system development stages presented in the paper include:
–– Infrastructure – chassis, controller and interface
connections for standard and high performance systems
–– Modular system start up – module selection, instrument
connection, interoperability and control
–– PXIe module control – instrument commands versus
–– Test system control – software programming environments,
such as C++, LabVIEW, and/or using application software,
such as X-series measurement applications.
Figure 1. Optical stressed eye instruments for N4917B.
An embedded PXIe controller, which plugs directly into the PXIe
chassis, is a good option for compact PXI systems that need
longer product life support than off the shelf PCs. Embedded PCs
provide data bandwidths comparable to remote PCs and now
offer more IO options. Processing speeds, in the latest standalone PCs and embedded controllers combined with the fast PCIe
backplane of the chassis, are able to achieve very fast overall
communication speeds for PXIe test systems.
03 | Keysight | Transitioning to a PXI Test System - Application Note
Star Configuration
Remote PC
PXIe chassis 1
PXIe chassis 2
For larger test systems, multiple chassis can be connected either
directly from the PC in a star configuration or the PC can connect
to one chassis and that chassis connects to the next chassis,
and so on, with interface/system modules creating a daisy
chain configuration. Typically, 2, 3 or up to 4 PXIe chassis can
be connected in a single star or daisy-chain test configuration.
Embedded controllers also support 2, 3 or up to 4 multichassis configurations. Examples of the star and daisy-chain
configurations are shown in Figure 2.
Daisy Chain Configuration
Remote PC
PXIe chassis 1
PXIe chassis 2
Embedded Controller Multi-chassis Configuration
PXIe chassis 1
PXIe chassis 2
Figure 2. PXI Star and daisy-chain chassis configurations
Modular system start up
With the controller and chassis set up, the next step is to add test
instrument modules. With so many PXIe stimulus, measurement,
and control modules to select from, engineers can choose from
a wide range of modules for the instruments that best meet their
current test needs and also enable flexibility and scalability for
future expansion. Additionally, PXIe instruments from multiple
vendors designed in accordance with the PXIe industry standards
are interoperable.
However, for each module you will have several software options.
For example, there can be limited driver types for programming
environments, options for additional measurement software for
specific applications, or other factors may affect how the module
performs in specific programming environment(s). As instrument
modules are selected, it is important for PXI system developers
to understand the PXI modules’ communication path - how
the module is controlled through software, and trade-offs in
programming time and test throughput. The following layered
description of PXI module communications will help you to make
those key PXIe module set-up decisions.
PXIe chassis 3
PXIe chassis 4
04 | Keysight | Transitioning to a PXI Test System - Application Note
Figure 3 illustrates the overall software architecture for a PXIe
test system. Beginning at the bottom, a specialized kernel driver
provided with the instrument module is used as a communication
interface between the instrument and the PCIe bus. The kernel
driver communicates with the virtual instrument software
architecture (VISA) within the IO software layer. VISA is an
established standard that provides a common programmable
interface used by test and measurement suppliers for instrument
The next layer consists of interchangeable virtual instrument
(IVI) drivers including IVI-C, -COM and –NET drivers, typically
supplied by PXI or AXIe module manufacturers. The drivers
provide a programming interface for engineers’ use with test
system software. Partitioning the software into the kernel, IVI
drivers, and VISA layers enables PXI module suppliers to provide
scalability and support for many different instruments. These
layers, or software additions to the test system PC, are required
to complete the instrument driver stack needed to connect
and communicate between the PC and instruments in the PXIe
chassis. The kernel, VISA, and IVI driver stacks work together and
form a tightly coupled group enabling co-existence of PCI driver
stacks from multiple vendors, as shown in Figure 4.
Example measurement applications
specific software
Signal Studio
89600 VSA
Waveform Creator
SW development
Instrument driver
Front Panel
IVI-C / IVI-COM / IVI -NET 1 Drivers
VISA – interface to HW
Kernel driver
Module Kernel Driver
Module or MMI (Multi-module Instrument)
Figure 3. Example of Modular System Software Architecture
05 | Keysight | Transitioning to a PXI Test System - Application Note
Co-existence of PCI driver stacks
PXI instrument drivers
co-exist as expected with
any other PCI drivers
IVI Driver
kernel driver
work together
and form
tightly coupled
VISA Library
Kernel driver
VISA driver installation
Module IVI installation
Figure 4. PCI driver stacks for mulit-vendor interoperability
Example: Keysight & NI PXI switches
installed in same system
IVI Driver:
IVI Driver:
06 | Keysight | Transitioning to a PXI Test System - Application Note
The next layer provides software programming environments
that are used to access and control the PXI modules once their
drivers are installed. Drivers can be accessed from program
environments like Microsoft Studio, Keysight VEE, LabVIEW and
MATLAB either directly or indirectly using a software wrapper
around the IVI driver as shown in Figure 3 for LabVIEW and
MATLAB. The final layer, application specific software, may be
used as a stand-alone test program, or may be integrated into
the software programming environment. Application specific
software, such as 89600 VSA software, Signal Studio, X-Apps
M90XA, and SystemVue provides specialized measurement and
analysis capabilities. Application software is created to reduce
the amount of programming required from engineer and also
ensure measurement accuracy and repeatability.
With a better understanding of the overall software architecture
for a PXIe test system you can now begin module set-up by
installing VISA and the instrument drivers for the modules you
have selected . There are several ways to verify the PC to module
connection and begin to communicate with the instruments.
These methods include the use of Microsoft Windows Device
Manager, Keysight’s Connection Expert, National Instruments’
Measurement & Automation Explorer (MAX), and soft front
Microsoft Windows Device Manager is readily available on
modern PCs and will display any PCI-based device that is actively
connected to the bus. A valuable tool during initial test system
start-up and debug, Windows Device Manager discovers and
verifies the connection of multiple vendors PXIe instruments.
Keysight Connection Expert helps with the initial connection
to modular instruments making it quick and easy. Keysight
Command Expert or National Instruments’ Measurement &
Automation Explorer (MAX) go a step beyond discovering and
connecting to instruments to provides instrument commands,
syntax checking and command execution for instruments that use
Standard Commands for Programmable Instrumentation (SCPI),
IVI-C, or IVI-COM drivers. Reviewing the convenient Command
Expert and MAX capabilities can help to ensure your startup
needs are addressed as you select the software for your test
Figure 5. Microsoft Windows Device Manager
07 | Keysight | Transitioning to a PXI Test System - Application Note
Keysight Command Expert
NI Measurement & Automation Explorer (MAX)
Command Expert is a free software application that provides
fast and easy instrument control in many PC application
environments. Provides all you instrument control in one
interface. Command Expert combines instrument commends,
documentation, syntax checking and command execution all in
one simple interface. Command Expert works with instruments
that use Standard Commands for Programmable Instrumentation
(SCPI), IVI-C, or IVI-COM drivers.
Measurement & Automation Explorer (MAX) is a free piece of
software that automatically installs with National Instruments
software and device drivers. Detailed, topic-specific help is also
included. (MAX) provides access to your National Instruments
CAN, DAQ, FieldPoint, GPIB, IMAQ, IVI, Modular Instruments,
Motion, NI Switch Executive, VI Logger, VISA, and VXI devices
–– Find instrument commands
–– View complete commend documentation
–– Verify command syntax
–– Build and execute instrument command sequences
–– Integrate sequences into PC application environments
–– MATLAB, Excel and Python Add-ons
–– Integrates with graphical programming environments
–– Configure National Instruments hardware and software
–– Back up or replicate configuration data
–– Create and edit channels, tasks, interfaces, scales, and
virtual instruments
–– Execute system diagnostics and run test panels
–– View devices and instruments connected to system
–– Updates National Instruments software
PXI instruments are provided with a soft front panel driver, a GUI interface that allows you to easily verify communication between
the PC and instruments create and execute instrument commands and display results. Soft front panels are most helpful during initial
startup and when troubleshooting or creating new instrument control programming code.
Figure 6. PXI Soft Front Panel
Microsoft Windows Device Manager, Connection Expert, MAX, and soft front panels provide the easiest and most efficient methods to
initialize PXI test systems.
08 | Keysight | Transitioning to a PXI Test System - Application Note
PXIe module control
Test system control
With modules plugged in and communication established, you
are now ready to determine how you will communicate with the
instrument within the automated test system. Choices include
using direct instrument commands such as SCPI, instrument
drivers, or a combination. SCPI commands, originally developed
for use with benchtop instruments, are not available for all
modular instruments. However, for instruments that provide
them, SCPI commands enable the use of instrument features not
supported by the available drivers and can be programmed into
test sequences by experienced programmers. SCPI commands
can provide the absolute maximum system throughput speed
because very specific commands for configuration, execution
and data retrieval can be optimized for specific applications. Test
developers often choose to use SCPI commands and invest time
in detailed programming to reduce overall test times.
The software environment and tools selected for a test system
will have a big impact on the system cost, usability during
development, and future maintenance or expansion. When
making a software environment choice, there are several things a
development engineer must consider:
Using a standard instrument driver is more common because
they are easier to use, and minimize the time required to program
command variables. Test developers who choose drivers want
to get the system up and running quickly and would like the
test to run fast and efficiently but are less concerned with
very high throughput. Different types of instrument drivers are
typically provided with the PXIe modules and support use in
certain programming environments and instrument features.
It is important, as PXIe instruments are selected, to ensure
they include instrument drivers for the software development
environment and all of the instrument features you plan to use.
Consider using industry standard IVI-COM (Component Object
Model) drivers that work with all popular PC languages and
types of IO. IVI-COM drivers also ensure a higher degree of
hardware and software interchangeability as well as software
maintainability. Basic communication and interoperability of
PXIe instruments from multiple vendors is assured by the wellestablished PCIe bus and today’s mature driver architecture
standards and installation methods.
Conditioning and
Data Conversion
Figure 7. Considerations when programming a PXI system from scratch
–– How complex it is to learn for development and future
–– How easy is it to use and integrate with other program
languages, devices from multiple vendors, or specialized
–– Can software be leveraged and reused for new test system
–– Will the program environment be supported over the long
–– What programming and development time is required
before you are generating results?
–– What are the pros/cons of creating a custom test system?
–– What are the pros/cons of creating a system that uses or
integrates application software for specific tests?
09 | Keysight | Transitioning to a PXI Test System - Application Note
Fortunately, many software development environments support
open standards, which in turn supports system flexibility
and configurability for SCPI commands and instrument
drivers, multiple devices from different vendors, and allows
easy integration of application specific software. To ensure
maximum flexibility during system development, look for
modular instrument vendors who provide software tools and
applications that support all of the leading test development
environments, including National Instruments LabVIEW,
LabWindows, Microsoft Visual Studio, Keysight VEE and
MathWorks MATLAB. Using application specific software that
works well in leading test development environments enables
test engineers to leverage and integrate measurement expertise
for simulation, measurement and signal generation. Application
specific software often includes support for standards-compliant
measurements, development of go/no-go tests, or application
specific capabilities like demodulation of complex modulation
schemes for example. These software applications are ready to
use as stand-alone test software, or can be integrated with your
test system saving development time and providing a high level of
measurement integrity.
With today’s demands for fast development of flexible test
systems, it makes sense for engineers to take advantage of the
benefits modular PXIe test systems have to offer. These include
lower cost of extremely configurable hardware and software,
less space, improved cabling, cooling, and execution efficiency.
It is important to have a clear system strategy before making
modular test system design decisions. Understanding the options
and pros and cons of each step of the test system hardware and
software design as demonstrated in figure 8, will help to achieve
successful development of a new modular test system.
Test systems that prioritize measurement speed use programs
written by engineers in programming environments such as C,
C++, C# and Direct IO commands to optimize test throughput.
These and other programming environments, use SCPI commands
to achieve the fastest test execution times. Although faster
measurements speeds are achieved for these test systems, more
program development time is required and the measurement
accuracy depends on the engineers’ code. Fast throughput is also
possible when using modern instrument drivers in programming
environments such as LabVIEW, LabWindows, Microsoft Visual
Studio, Keysight VEE and MATLAB and the drivers help to provide
recommended parameter configurations.
Application Software vs. Instrument Drivers
Different PXI Users Have Different Goals
User A
User B
Functional test, e.g.
radios, RF modules
Typical Application
(10’s to 100’s of sec.)
Test throughput
Efficient use of: mfg. space,
engr. time, legacy systems.
“I don’t need/want to
become a PXI expert.”
Component test, e.g.
Very high
(1 sec or less)
Speed. Speed. Speed
Value sought
Baseline solution
“I’ll invest in heroic efforts
for a 100 us improvement.”
Figure 8. Trade-offs when using application software versus instrument drivers
10 | Keysight | Transitioning to a PXI Test System - Application Note
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Published in USA, July 20, 2016
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