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.
This is what I love about the Sherlock Ohms postings. You can turn the equipment upsidedown to find the problem, but in the end, it was a line that had to be drawn darker. This is a common solution to difficult problems -- look at what was difficult at an earlier stage in the equipment's development.
So they were able to fix a CT scanner by drawing a line with black ink...Sometimes, I think it takes a better "detective" to find find a simple solution, like this one.
I agree, Chuck. Like many of the Sherlock Ohms blogs, it's hard to imagine how they figured out such an off-the-wall solution. It is certainly not intuitive. The trick here was remembering something odd from the past.
I would guess they went for a permanent stripe, since they would know that the improvised ink line would eventially fail, just as the frist improvised ink line failed.
Yes, this is the second temporary repair. In some ways the first temporary repair is the most suprising since it sounds like it was done by the vendor during the installation process.
There was no final fix in this story, Ann. Perhaps we'll see another Sherlock Ohms story in a couple years when the next set of engineers try to figure out this eventual failure.
Sounds like a bad way to repair something. Could they have not repaired the wheel with a permanent solution. They should have replaced the wheel with a new and good one.
If I were their manager, I would not have allowed that type of repair. It will come back to haunt someone else in the future.
I guess in today's highly regulated environment, this temporary black pen fix would not be enough. In addition to solving the problem immediately, a root-cause countermeasure would also be needed to be performed by the equipment manufacturer so this problem would not occur again years later.
Insufficient contrast is a very subtle failure mode indeed. The system goes from functioning to intermittant to failed and nothing shows up as the cause. Hartridge has a similar problem with the linear encoders in their fuel injector system teststands, except that it is dirt, not fading. The normal fix is a new encoder for about $450, and two hours wait, and hope the new encoder is in stock. My cheap fix was to clean the scale in the encoder with denatured alcohol and a soft lense wipe tissue. Materials cost is about ten cents and the labor time is about five minutes and no recalibration is needed. But the profit is less, so the customer gets the _____.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 5
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This radio show will show what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
12 
