Pickering Interfaces' Blog - Insights into Switching Technology

Bob Stasonis

Recent Posts

Simplifying Test Interconnect with Pickering’s Cable Design Tool

Posted by Bob Stasonis on Apr 6, 2020 5:34:31 PM
Simplify test interconnect

Correct interconnect products need to be selected once instruments and switching products have been chosen for a test set-up. This can be a complex process while checks are made, resulting in a significant investment in time, money, and in some cases, even exceeding the initial purchase cost of the devices.

The cable design for a test system is probably the last section of a test system development. And because proper cabling is critical for repeatability and accuracy, it needs care and expertise. Depending on the application, the test engineer needs to consider test specifications, including voltage, current, temperature, insertion losses, and more. From there, the engineer needs to determine the connections between the instrument and the Device Under Test (DUT), and then select connector types, backshells, wire length, and wire types. Unless the test engineer is an expert on cabling, researching wires and connectors can be a daunting task.

As a leader in test and measurement switching and simulation for over 30 years, we fully understand the importance of high performance and reliable interconnection between the component parts of a test system and DUT. That is why we established our own in-house connectivity division that manufactures a comprehensive range of 1200+ high-quality cable and connector solutions. There are times, however, when a standard cable assembly is not suitable, and there is a need for custom connectors and wire types or specific harness wiring. Pickering's free online Cable Design Tool (CDT) is a simple and efficient way of creating these custom cabling solutions.

Pickering's Cable Design Tool and completed cableThe cable itself can be drawn in a few clicks, choosing connectors, backshells and wires from a library. Linking them together is achieved manually by clicking on pins, or an auto-link option will link user-selectable groups of pins in 1-1 order. A third option is to use the CSV import, where the pinout with signal names can be prepared in an Excel sheet.

Currently, there are around 500 connectors and 400 types of wires and cables in the library (which is growing daily). These can be selected by many attributes, including pin count, connector type, rated voltage, conductor count, insulation type, conductor size and more. Many sophisticated functions, such as screening, sleeving and labels, bundling, and much more, can also be added. 

When the design is completed, the tool creates the full datasheet with all part numbers, lengths, labeling and pinout map for each path which can be downloaded in PDF format. Also, if the customer decides to work with Pickering, it can be used as build instructions for their production department. Otherwise, the customer is free to take the design and solicit other cable vendors.

Cable Design Tool data sheet

The tool is collaborative, enabling several people to work on a design, and once finished, the design is then sent to us to review. Our cable technicians can assist by suggesting cost-saving design changes and optimize the design for ease of manufacture by using stocked parts. Lead time is typically four to five weeks after receiving the order.

The main advantage offered by our connectivity division is the ability to provide precisely what you need. Our flexibility starts with the first point of inquiry. Our technicians receive cable drawings in many formats—AutoCAD, Visio documents, Excel pinouts, text descriptions, etc. They can analyze, design and manufacture complex custom cable harnesses. Our designers are there to help, whether modifying existing designs or designing new ones, our in-house production is flexible to cope with such demands and can manufacture in single quantities or high volume.

Start Using The Tool 

Take a look at our on-demand webinar "Simplifying Test Interconnect with Cable Design Tool" here >>

To learn more about cabling for your automated test system, take a look at our SwitchMate book, there is a whole section to help you understand it.

Cabling for your automated test system - Switchmate

Have questions or need more information? Please contact us here.

Topics: automated test system, software, Cables and Connectors

Moving Your Test & Measurement System from VXI  to PXI : Not If, But When

Posted by Bob Stasonis on Oct 31, 2017 9:21:02 AM

Moving from VXI switching to PXI switchingIn its day, VXI technology was a definite step forward. Built upon the modular VME computer bus, VME eXtensions for Instrumentation, or VXI, reduced the size and increased the performance of high-end test systems. Instead of bulky rack-and-stack systems, whose instruments were connected by the relatively slow GPIB interface, VXI systems featured modular instrumentation that plugged into a modified VMEbus that provided higher data transfer rates and real-time performance not possible with rack-and stack systems.

The VXIbus has served test & measurement engineers well, but it is more than 30 years old now, and it may be time to move to a more modern platform. Today, more test systems designers are choosing the PCI eXtensions for Instrumentation (PXI) platform when designing new modular test systems or replacing or updating existing test systems. Originally introduced in 1997 by National Instruments, PXI is now supported by nearly 70 companies working under the umbrella of the PXI Systems Alliance (PXISA), which publishes the PXI specification and ensures instrumentation interoperability.

PXI's main advantages: availability and lower cost

PXI's biggest advantage over VXI is product availability. In the nearly 30 years since VXI was introduced, the Consortium that manages the specification has gone from over 40 companies down to just eleven members. Even Pickering has dropped their VXI line due to key part obsolescence and reduced market requirements. A large number of the products that were available in VXI in the past are now obsolete and are often only available on the used market. That is not to say that VXI is no longer viable. In some specialized applications like Data Acquisition, there are VXI vendors producing new products. In other applications, VXI is mostly recommended for legacy applications and not for new designs.

A second reason to look closer at PXI for your test & measurement needs is that hardware costs are lower than VXI. Because PXI is based on the PCI bus, which is used in many personal computers, it can take advantage of the advances being made to serve the PC marketplace. Because many of the components used in PXI modules are also used for PCI modules, they cost less because so many more of them are made. This leads to overall reduced cost for PXI modules when compared to VXI modules. PXI systems typically cost one-half to one-third the cost of an equivalent VXI system.

Some of the other advantages that PXI enjoys over VXI include:

  • Data transfer. Standard PXI can transfer data that is 8, 16, 32, or 64 bits wide. VXI can only transfer data that's 8, 16, or 32 bits wide.
  • Data throughput. Because PXIe (Express version of PXI) systems can transfer data over high speed serial busses, the maximum throughput for PXI systems is higher than that for VXI systems. The maximum throughput for VXI systems is only 160 Mbytes/s, while the maximum throughput for PXIe systems is 12 Gbytes/s.
  • PXI modules are smaller than equivalent VXI modules. In fact, PXI systems have the smallest footprint of any open-architecture instrumentation system. This is a big advantage for PXI test systems because as test systems become more complex, test system developers need to cram more functionality into their test systems. PXI lets them do this while at the same time keeping test system size manageable.
  • Instrument availability. Aside from perhaps some very specialized instrumentation (an example would be Bustec with their specialized data acquisition systems), whatever you can buy in VXI, you can also buy in PXI. And, the trend is clear. There are fewer new VXI modules being developed than new PXI modules, and that will continue into the future as more designers specify PXI over VXI. In some applications, such as fault insertion during simulation, there are no VXI modules available. Also, because PXI is based on the CompactPCI specification, you can use CompactPCI boards in a PXI system.

Making the right choice

While the availability of PXI switching and instrumentation modules makes the choices relatively easy, there is the issue of migrating test programs from VXI to PXI, specifically in switching applications. The ability to replicate original test configurations to support legacy FRUs (Field Replaceable Units) is important to continue supporting older test programs while planning for future requirements.

To help ease this transition, we have developed PXI switching and simulation modules that closely match the operation of VXI switching modules from Racal, VTI Instruments, Agilent (Keysight), and other manufacturers. And, our policy of supporting our PXI Switching products for 15 to 20 years, or even longer, means that your next-generation test systems will have as long a life as their predecessors. An example of our VXI to PXI can be seen below.

Pickering's VXI to PXI switching cross-reference.

Our PXI modules listed in the table above are in many cases a close equivalent to the VXI modules. Because of the large PCB real estate of C-Size VXI modules, channel counts may be different, and specifications may not be exactly the same. Depending on your application, a different Pickering PXI module may be closer to your requirements than what is shown here. We also have cross-references to other manufacuturer's VXI switching.

Take a look at our VXI to PXI Cross-Reference here

Please contact our support team for more assistance in finding the correct module for your requirements.

Migration issues

While PXI is clearly the modular platform of choice when designing new test & measurement systems or upgrading existing systems, you may encounter some issues when doing so. One of them is module real estate. Clearly, a C-size VXI module has a lot more area to mount components, meaning that some VXI modules may have more features or functionality than a PXI module that you might choose to replace it. On the whole, however, VXI module designs are not as dense as today’s PXI module, so this is usually not an issue.

A related issue that you will have to address when migrating to PXI is cabling. VXI modules have a wider front panel (1.188-in.) than PXI modules (0.8-in.), meaning that many of the connectors used in VXI systems cannot be used in a PXI system. So, plan on building or buying new cables or buying adaptors.

If your instruments dissipate a lot of power, you may have cooling issues when migrating to a PXI system. The PXI cooling spec is less stringent than the VXI specifications, and generally, PXI chassis do not have the cooling power of VXI chassis. You may use multiple slots to achieve the necessary cooling.

Software is another area of concern. There is no easy way to migrate test programs. But, given the number of good test-development software packages available for the PC platform, this may not be as big an obstacle as it might appear.

Despite these drawbacks, if you're an automatic test system developer, the question is clear. It's not if, but when you should move to PXI-based systems from VXI. The answer is pretty clear, too. The answer is now.

Let us know your thoughts on moving from VXI to PXI.

Topics: PXI Switching, automated test system, test and measurement systems, VXI Switching