Retrofitting Rack-Mount Based ATEs Using PXI Modules for Virtual Instrumentation

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NI PXI Chassis serve as virtual instrumentation in this application from WinSoft.

Author(s):
Ehud Shany - WinSoft Inc.

Industry:
Government/Defense

Products:
LabVIEW, PXI/CompactPCI,

The Challenge:
Replacing rack-mount instruments with PXI-based modules without modifications and re-validation of the existing software. In addition, the solution should address the problems associated with different type of communication protocols, timing, undocumented commands, and change of signal characteristics.

The Solution:
Developing and implementing a real-time emulator that uses PXI modules as a virtual instruments to maximize the use of the modules while reducing the footprint of the ATE. The existing software remains untouched and new software is written in LabVIEW.

A growing number of instruments that reside in exiting ATEs are becoming obsolete and replacement spare parts are unobtainable. The goal of current ongoing ATE retrofitting projects, mainly in the military community, is to reduce the size of the testers by replacing the instruments with a new, smaller version. One of the best options is PXI virtual instrumentation modules.

The cost of replacing the existing hardware often implies a software change and potential communication protocols to accommodate different functionality. Additionally, changes to the software require system re-certification, which increases the total cost of the process.

An ideal retrofit process should include the following elements:

• Support of PXI modules as standalone modules or as a virtual instruments via several protocols such as GPIB and TCP/IP
• Reduction of the ATE size (i.e., from 3-bay size to 1-bay size)
• A modular approach in which the ATE is retrofitted through time while keeping some of the old instruments active until a new budget is allocated
• No changes to the software required regardless of the programming language, communication protocol, timing differences, mix of old/new instruments, and quality of signals.

PXI Modules as Virtual Instruments

The U.S. Navy faced a growing number of problems with its existing ATEs. It developed a real-time emulator  to provide a virtual instrument based on a collection of PXI modules (detailed list is provided later on). In a “traditional” ATE, a rack-mount instrument is connected to a CPU through GPIB bus. In Figure 1, the “new” instrument is a PXI chassis with module(s) that offer the same functions as the old instrument. The CPU still sends and receives the same commands as it did in the past. The communication between the CPU controller and the instruments translator/emulator module is done via the existing GPIB bus and the communication between the translator/emulator and the PXI modules by using a TCP/IP protocol. Each command and/or address sent by the CPU controller is analyzed and translated in real time in to one or more command(s) of the new PXI modules that is connected to the bus. The new instrument’s reply is treated in the same way. Please note that it is possible to use the same PXI modules for emulation of different GPIB instruments. For example, some of the channels of PXI relay-switch card are used to emulate an old HP scanner and the other channels of the same PXI card to emulate an interface device (ITA). In other words, the emulator makes it possible to use a group of PXI cards (or sometimes a part of one PXI card) as a ‘virtual’ instrument.

Note: At the time that this paper was written, we conducted an R&D project in which the real-time emulator resided as part of the PXI controller (Slot 0). This eliminates the need for external emulator.

The number of instruments supported by one instrument translator/emulator module is limited only by the number of PXI slots. If required, we can add a second PXI chassis for more modules. As more and more chasses are added, it is easy to convert a 3-bay ATE to 1 or half bay ATE, which can host the several PXI chasses.

The instrument translator/emulator uses different combination of the above module as a virtual instrument. For example, the PXI switch and PXI DMM are used as a scanning DMM.

The instrument translator/emulator is installed under the monitor (on top of the PXI chassis) and takes only 1U of space. A Virginia Panel interface serves as new interfaces for the Unit Under Test (UUT). The original ATE is 3-bay in size and is used for radio testing by the U.S. Navy.

The presented technical solution deals with the communication level only (GPIB or others), although it is not required to have the TPS source code available and the programming language of the TPS is not affecting this technical solution.

The instrument translator/emulator module, as part of its functionality, resolves all GPIB (or other protocol) addressing and other special communication packages and messages. It supports several modes, including “transparent mode”, in which it passes the commands through without any action. With this setup, engineers can add new instruments to a legacy ATE system while the ATE is undergoing several steps of retrofit.

Adding LabVIEW to Existing ATE

The above configuration enables the U.S. Navy to preserve all of its TPSs (ATLAS and HP-Basic). New TPS are written in LabVIEW and they coexist with the old TPS.

The following paragraph is from the Navy Newspaper (OutLook, September 2005):

“Phase lasted for five months and included a complete retrofit of the ATSs’ cables and RF switches. Phase II took six months. At the end of this process, the ATSs IPT calculated a cost avoidance of over $2 million during Phase I and cost avoidance of more than $12 million during Phase II allowing an additional five ATSs’ platforms to be upgraded within budget. An overall cumulative cost avoidance of $22 million was calculated for all seven ATSs’ platform upgrades. This calculation is based on the Department of Defense costs for rewriting and revalidation of the more than 200 TPS. The down-time of the upgraded ATSs’ platforms that utilize the WISE Technology went from 50 percent to less than 2 percent.”

For more information, contact:

Ehud Shany

WinSoft Inc.

Santa Ana, CA

Tel: (949)428-4844

E-mail: ehud@winsoft.com

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