Slowly, over the last four decades, industry has gradually begun to give Design for Testability the attention it truly deserves. This concept was originally pioneered by Ralph De Paul, Jr. in the mid 1960’s based on diagnostic ideas that he had developed in the 1950’s. At that time, industry was not yet receptive to the idea of implementing within the design process new techniques oriented solely toward improving the testing and “troubleshooting” of a device or system. During its first two decades, Design for Testability remained largely an “outsider” discipline, accepted only by a relatively small group of industry experts, until the idea finally began to take hold in the mid 1980’s.
The Initial Two-Decade Investment
In the 1960’s and early 1970’s, De Paul—who would later found DETEX Systems (today’s DSI International)—began pushing for innovative ways to assure our servicemen of dependable equipment in the field. Recognizing that this was best insured during the design process, De Paul developed a way of representing design functionality as a causal model in what he called Design Disclosure Format, or DDF (later to be known as a dependency model). With DDF, Maintenance Dependency Charts (MDCs) were developed to improve troubleshooting and equipment maintenance. The DDF approach would prove to be equally effective for electronic or non-electronic systems. Emerging from this process in the mid 1960’s was military standard MIL-M-24100, co-developed by Ralph De Paul and the first precursor to future Testability standards. A careful study of this initial standard would reveal that at its core was a design description format that was nearly identical to the format used by LOGMOD—DSI’s first commercially available Testability and Maintenance tool.
With LOGMOD enjoying continual field successes through the late 1970’s, United States Department of Defense studies were conducted and William Keiner (US Navy) sought out DSI and Ralph De Paul to bring this need for Testability analysis before the U.S. congress. Keiner visited DSI on numerous occasions and was ultimately credited with authoring MIL-STD 2165, the first recognized “Testability” standard. This document, however, was heavily influenced by the ideals, techniques and writings that De Paul—ever the diagnostic evangelist—had freely shared with Keiner during this period.
As a result of DSI having been intimately involved in the initial “push” of MIL-STD 2165 (now, MIL-HDBK 2165), DSI was also instrumental in the development of MIL-HDBK 1814, the Integrated Diagnostics standard. The purpose of this document was to better define the broadening scope and diagnostic responsibilities of all contributing parties, both those involved design and support activities. This was the era where Design for Testability began to branch into additional areas and the multitude of design and support disciplines began to coalesce into a more unified diagnostic engineering process that was better suited to evaluate diagnostic performance and support objectives during the design phase of large scale complex programs.