Manufacturers of switching hardware for automated testing have been talking up the concept of so-called “smart switching” for production test applications for close to two decades. In the early ‘90s, smart switching typically referred to programmable switch mainframes capable of storing switch patterns and sequences for later use in test sequences. Built-in scan control capabilities made it unnecessary for the system controller to oversee every step of the test procedure because the switch mainframe itself could be programmed via SCPI commands to control channel spacing, scan spacing, and the number of scans.
A built-in non-volatile memory could store hundreds of complete switch patterns. SCPI provided a uniform and consistent language for the control of test and measurement instruments, so the same commands and responses could be used to control corresponding instrument functions in SCPI equipment, regardless of the manufacturer or the instrument type.
Fortunately for electronic components manufacturers, who face ongoing pressure to reduce cost of test by boosting throughput, some switch hardware vendors continue to invest in the development of smart switching technology using more sophisticated on-board testing intelligence.
For example, some new designs employ an embedded Test Script Processor (TSP) that offers users enhanced capabilities for controlling test sequencing/flow, decision-making, and instrument autonomy. Users program and communicate with TSP-enabled instruments in two ways: either by executing individual TSP commands (similar to sending individual SCPI commands) or by writing test scripts.
Designed to reside on the instrument or switch mainframe itself, such scripts are a collection (list) of instrument control commands and/or program statements that can be executed on command. The use of these scripts can eliminate the transmission time from the PC to the switch system because all commands and statements in the script are executed by the mainframe. For switch mainframes equipped with an LXI interface, all TSP configuration and script loading and data transfer can be performed via this interface.
Some of these switch mainframes provide a programming interface that allows users to create powerful, high speed, multi-channel tests to download into either the unit’s volatile or nonvolatile memory. Using the downloaded script, the unit controls itself, independent of the system’s host controller, freeing up the system controller to interface with the other equipment in the test rack more frequently, thereby increasing the overall system throughput. For example, Keithley’s Model 3706 System Switch/Multimeter mainframe has very deep memory; its program memory can hold 50,000 lines of code and its data memory can store at least 650,000 readings.
What does the continuing evolution of smart switching mean for component manufacturers? For those prepared to invest in their test lines to exploit the newest technology, it can mean up to a four-fold improvement in test system throughput under some circumstances. TSP is a very flexible hardware/software architecture that allows many different implementation choices.
The primary tradeoff is programming complexity vs. throughput. Relatively simple programming techniques will allow noticeable throughput improvements over the use of more traditional single-command transfer methods. Slightly more complex programming can produce dramatically higher throughput gains.
About the author:
Jennifer Cheney (firstname.lastname@example.org) is a Senior Applications Engineer at Keithley Instruments, Inc., headquartered in Cleveland, Ohio. She earned a Bachelor of Science degree in electrical engineering from Case Western Reserve University in Cleveland. She has been assisting Keithley customers with instrument applications since 2001.