Long before high-speed digital data acquisition, before laptops on carts and touchscreen instruments in the lab, there was the glow of a cathode ray tube (CRT). In the early 1950s, engineers like Greer Ellis and Francis G. Tatnall were pushing the boundaries of experimental mechanics using CRTs to capture dynamic stress-strain behavior — not just for static loads, but for shock, vibration, and high-frequency impacts.
The article they co-authored, “Stress-Strain Records at High Straining Rates,” describes how they used dual-axis X-Y recording to map load-deformation curves in real time. With nothing more than strain gauges, bridge amplifiers, and a Dumont 304-A oscilloscope, they produced oscilligrams of material behavior under extreme loading rates — sometimes down to 0.001 seconds per cycle. These methods laid the groundwork for the real-time diagnostics we rely on today.
🧠 Why Should We Still Care About CRTs?
CRTs themselves are obsolete, but the legacy they left behind is not. They were foundational to the development of modern eddy current testing instruments.
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Dr. Friedrich Förster, the father of eddy current testing, was using CRTs in the 1940s to visualize impedance changes.
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Hugo Libby, another pioneer in electromagnetic NDT, did most of his multifrequency development work using CRTs. His instruments relied on visual signal interpretation, not unlike the analog scopes used in early flaw detectors.
Understanding this history helps us appreciate the evolution of NDT technology — and reminds us that today’s automated, digital, AI-powered test platforms stand on the shoulders of innovators who worked with glowing tubes, vacuum diodes, and analog signals.
⚡ From Oscillograms to Algorithms
As engineers today, we benefit from that analog-to-digital journey. Modern eddy current testing systems still rely on impedance phase and amplitude — but we now process them through software, automate detection routines, and even model flaw responses using finite element tools.
Yet the principles haven’t changed. What the early CRT pioneers showed us was the value of visualization, repeatability, and a passion for understanding materials under real-world stress conditions.
Let’s not forget where it all started.
🔗 Explore more about the history, evolution, and future of eddy current testing at eddycurrent.com — the most comprehensive resource for anyone working in electromagnetic NDT.