My first proper position as an engineer was classified as a Grade 4 Medical Physics Technician at the London Hospital’s Physics Research Labs in Whitechapel.
My main role at the time was working with the department's physicists to design, prototype, and construct medical and scientific electronic instrumentation. A few months after we received the hospital's first CT scanner, it stopped working.
The tomography in those days was performed by a large rotating gantry which housed the X-ray tube. The gantry would rotate a small number of degrees and then halt, fire the X-ray, then rotate again. This would continue until the required 3D image had been captured by the mainframe computer controlling it.
For some reason, the gantry refused to rotate. First, the maintenance technicians went over the equipment to see if they could figure out what was wrong. Next, a couple of physicists looked it over. Then we called in the company techs. At this point, there was a waiting list of patients who needed a CT scan, and there were not many other facilities we could send them to.
After a lot of head-scratching, program debugging procedures, rebooting endless times, circuit board removal/checking/replacing, and connection testing, one of the company techs remembered something. The graticules on the transparent perspex disk which allowed the opto-electronic sensor to measure the gantry angle had been contracted out to a manufacturer that specialized in that kind of work. An error by the manufacturer on this early production unit had resulted in one graticule being missed.
This error was picked up by the company and, as a temporary fix, it drew a line in black pen by hand. That enabled the system to synchronize. Apparently, over time, this line had become faint until it reached the point where it no longer performed the required function. That turned out to be the cause of the failure. We drew a new line with a black pen, and that new line fixed the whole system on reboot.
This entry was submitted by Daniel Indyk and edited by Rob Spiegel.
Daniel Indyk worked for 10 years as an electronics engineering officer in various R&D positions. He then continued his studies to obtain an M.Sc in Electrical Engineering and an M.Eng.Sc in Power Engineering. He is now a Chartered Professional Engineer and Chartered Physicist working in the power industry in NSW, Australia.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
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