Photographer: Bernie Bruner, Rocky Mountain Test Equipment
The term switching systems has been an EE editorial calendar topic only since the 1980s. Before that, in keeping with the magazine’s component reliability and evaluation engineering focus, individual switches were covered—for example, thumbwheel switches in 1969, solid-state relays in 1974, and switches and relays in 1983.
Switches of several types, keyboards, and relays were featured again in 1987, and in June of that year, EE published an article about the CSW10 Custom Switch Module for the Summation SigmaSeries TestSystem. This test system was discontinued after John Fluke Manufacturing bought Summation in 1991. Nevertheless, many of its triggering and synchronization concepts and its use of modular plug-in instruments were innovative and attracted a strong engineering following. Switching included the guarded 20-channel HAS10 High-Accuracy Switch, the 6-channel HFS10 High-Frequency Switch, and the CSW10 Custom Switch Module for a customer’s specific switching functions.
The Summation system predated VXI and, according to a Geotest-Marvin Test Systems article published by EE in 2003, was an impetus for its development. Today, 20 years after the SigmaSeries was discontinued and attesting to its popularity, Geotest-Marvin Test Systems still markets the TS-305 ATS as a PXI-based replacement.
Generally, switching systems take two forms: either they are modular, based on VXI, PXI, or a proprietary form factor, or they are not. During the 1990s and 2000s, VXI and PXI dominated the magazine’s coverage of switching systems. LXI was introduced in 2005, and companies such as Pickering Interfaces redesigned switching functions previously developed as PXI modules to be compatible with LXI.
As explained by Pickering Interfaces’ Keith Moore, managing director and founder, and David Owen, business development manager, emerging standards have seen a progression of developments as modern computing platforms evolved, first with the adoption of GPIB and more recently, VXI, PXI, and LXI.
“PXI provides a convenient way of implementing smaller switching systems in a multivendor test system where it can coexist with instrumentation modules,” Moore commented. “LXI is a more effective and robust solution for larger switching systems and applications requiring control at a distance, which is inconvenient for other control interfaces.”
Larger 19-inch rack-mount chassis allow much more flexibility than VXI or PXI in the design of big switching systems. Several companies including Cytec, Universal Switching, Pickering, and Agilent Technologies have developed integrated switching products. Pickering, Cytec, and Universal have used the bigger chassis to address large matrices without requiring extensive cabling between sections. Other companies specializing in RF/microwave switching, such as Giga-tronics and Agilent, have accommodated more channels of physically large coaxial relays.
In 2001, EE published an ASCOR (now part of Giga-tronics) tutorial, “The Importance of Switching.” It defined various switch configurations and highlighted the role of shielding. In particular, a well-designed RF/microwave switch should maintain the controlled impedance of the connecting cables.
Continuing the emphasis on careful switch selection, complementary Signametrics articles that ran in 2006 and 2007 explained in detail the effect of switch resistance on low-level measurements. In 2007, we also covered optical switching as well as subminiature MEMS switches.
Switching systems provide the infrastructure that simplifies application of the individual switching elements. Nevertheless, it is the reed relays, MEMS switches, electromechanical relays, optical switches, and solid-state devices that carry the signals and determine the switching channel’s characteristics. “Testing Techniques to Improve Relay Reliability,” an article from Relay Testing Services, ran in 2005 and, reminiscent of the magazine’s original focus, presented results as Weibull plots relating the probability of failure to the number of operations. In 1970, EE published a page of Weibull plotting paper as a service to our reliability engineering readers.
As well as reed and electromechanical relays perform, solid-state switching continues to increase the RF and microwave applications it addresses. EE’s switching systems special report for November 2011 highlighted products such as Pickering’s 6-GHz FET-based 40-88x RF/microwave switches and the very compact solid-state National Instruments PXI-2536 544-Crosspoint Switch Matrix.
Regardless of the switching technology being discussed, EE will continue to bring you timely and technically interesting coverage as we begin our second 50 years of service.