Keysight Technologies PXI Test System Application Note
Below you will find brief information for PXI Test System. This application note outlines the transition from benchtop test instruments to a PXI or AXIe system with the help of Keysight technologies. This note provides detailed information on the PXI system infrastructure including chassis, controller, and interface connections. It discusses different aspects of the PXI system, such as modular start-up, interoperability, and communication path. This guide will also help you to get started with the PXI system and to understand the software architecture involved.
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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
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 System Infrastructure
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 drivers
– Test system control – software programming environments, such as C++, LabVIEW, and/or using application software, such as X-series measurement applications.
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.
Figure 1. Optical stressed eye instruments for N4917B.
03 | Keysight | Transitioning to a PXI Test System - Application Note
Star Configuration
Remote PC
PXIe chassis 1
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.
PXIe chassis 2
Daisy Chain Configuration
Remote PC
PXIe chassis 1
PXIe chassis 2
Embedded Controller Multi-chassis Configuration
PXIe chassis 1 PXIe chassis 2 PXIe chassis 3 PXIe chassis 4
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.
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 communications.
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.
Application specific software
SW development environments
Instrument driver
VISA
Kernel driver
Example measurement applications
X-Apps 89600 VSA
Signal Studio
Waveform Creator
SystemVue Other
Drivers
LabVIEW
Soft
Front Panel
LabVIEW
Driver
MATLAB
WIN CVI Visual
Studio
VEE
MS
Excel
Command
Expert
MATLAB
®
Driver
IVI-C / IVI-COM / IVI -NET 1 Drivers
VISA – interface to HW
Module Kernel Driver
Hardware
Module or MMI (Multi-module Instrument)
Figure 3. Example of Modular System Software Architecture
05 | Keysight | Transitioning to a PXI Test System - Application Note
PXI instrument drivers co-exist as expected with any other PCI drivers
Co-existence of PCI driver stacks
Controller
Application software
Example: Keysight & NI PXI switches installed in same system
Application software
IVI Driver
IVI, VISA and kernel driver work together and form tightly coupled group
VISA Library
IVI Driver:
(AgMSwitch.dll)
KeysightVISA
IVI Driver:
(niSwitch_32.dll)
NI-VISA
Kernel driver
Kernel driver
(AgMSwitch.sys)
Kernel driver
(niswdkw.sys)
VISA driver installation
Module IVI installation
Figure 4. PCI driver stacks for mulit-vendor interoperability
PCI module
Keysight
Switch module
NI
Switch module
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 panels.
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 system.
Figure 5. Microsoft Windows Device Manager
07 | Keysight | Transitioning to a PXI Test System - Application Note
Keysight Command Expert
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.
– 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
NI Measurement & Automation Explorer (MAX)
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
– 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
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.
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.
Test system control
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:
– How complex it is to learn for development and future maintenance?
– How easy is it to use and integrate with other program languages, devices from multiple vendors, or specialized applications?
– Can software be leveraged and reused for new test system development?
– Will the program environment be supported over the long term?
– 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?
Physical measurement
Signal
Conditioning and
Data Conversion
Digital
Signal
Processing
Figure 7. Considerations when programming a PXI system from scratch
Measurement
Software
Insights
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.
Summary
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
Size,
Cost
User A
User B
Typical Application
Functional test, e.g. radios, RF modules
Moderate
(10’s to 100’s of sec.)
Efficient use of: mfg. space, engr. time, legacy systems.
“I don’t need/want to become a PXI expert.”
Test throughput
Value sought
Mindset
Speed
Component test, e.g.
PA, FEM, RFIC
Very high
(1 sec or less)
Speed. Speed. Speed
“I’ll invest in heroic efforts for a 100 us improvement.”
Baseline solution
Application
Software
User-written,
Driver-based
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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Key features
- Transition from benchtop instruments to PXI and AXIe systems
- PXI system infrastructure
- Modularity and scalability of PXI
- Software architecture
- Communication path
- Module control