Comment by egocodedinsol
9 years ago
Sent this to my father, a control systems engineer. He responded with his own story:
"This is a true story which I saw with my own eyes. In Arkansas... It was in the afternoon, at a boiler plant. Boilers have an induced draft fan that pulls combustion products from the combustion chamber. A big, big fan with an electric operated throttling damper.
The damper began behaving erratically and the operator jumped up, grabbed a firehose and started hosing down the actuator housing. I asked him what was going on. He said that the actuator had overheated and he was cooling it down and went on about it being a bad design.
Anyway, the actuator began working properly. He said this happens when the sun shines on the unit etc. And it was a bad design etc., Etc.etc
Then it happened again at 11:00 PM. Same story. I asked him about the fact it was cooler and the sun wasn't shining on it. Don't recall his answer but he explained it all away, got the fire hose out and fixed it and I got the bad design lecture again.
Turned out to be a loose wire. The shaking from the fire hose always fixed the problem temporarily and reinforced his belief.
He was truly disappointed."
Shaking things often fixes problems. This reminds me of the following story:
> [O]ne of the earliest [applications] of dither came in World War II. Airplane bombers used mechanical computers to perform navigation and bomb trajectory calculations. Curiously, these computers (boxes filled with hundreds of gears and cogs) performed more accurately when flying on board the aircraft, and less well on ground. Engineers realized that the vibration from the aircraft reduced the error from sticky moving parts. Instead of moving in short jerks, they moved more continuously. Small vibrating motors were built into the computers, and their vibration was called dither from the Middle English verb "didderen," meaning "to tremble." Today, when you tap a mechanical meter to increase its accuracy, you are applying dither, and modern dictionaries define dither as a highly nervous, confused, or agitated state. In minute quantities, dither successfully makes a digitization system a little more analog in the good sense of the word.
— Ken Pohlmann, Principles of Digital Audio
> Shaking things often fixes problems.
Oh, indeed. I remember my father, a disabled former engineer, having an expensive McIntosh audio system. He was always fiddling with it, fixing it, applying anti oxidation spray, etc. My parents decided the large wall furniture (in which the audio system was, together with books, TV, etc) was to be replaced.
It turned out that during the giant relocation one of the compartments of his system (IIRC it was the tuner, but it might have been the pre-amplifier or amplifier as well) had become broken. My father, who was nearly blind, made it his project to repair the installation. He was failing, and my parents discussed sending the broken part of the audio system back for repair which would set us back a large sum of money.
Then, at some point, there was an earthquake of 5,5 on the Richter scale. (Having just looked it up the epicenter being 5,8 it was the largest earthquake ever registered in The Netherlands.)
The damage: a photo of a family member, protected by glass, had fallen and the glass was broken. In our wall, a rift appeared. Many things just weren't on their correct place. The radio? Ah, the radio. It worked again when it was put on!!
A similar phenomenon occurs with aircraft altimeters. They move smoothly in small propellor planes but tend to stick and then jump maybe 50ft at a time in gliders. Tapping the altimeter is standard procedure if you want to see small movements.
And also with humans! Vibrating insoles can make the elderly less prone to falls, because adding noise can bring the signal of differential pressures on parts of the foot high enough for them to feel that they're off-balance before they're unable to recover.
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Or as Arkwright always said "just j-j-jiggle it a bit".
It can also help with some occasional minor digestive issues.
A classic!
I had a mouse that would stop working occasionally. The pointer would jigger and shake, or get "sticky" on some parts of the screen.
After a few weeks I narrowed the problem down, it happeneed in the late afternoon, but it worked fine in the evening. It also worked when it was raining.
So it had something to do with the sun shining through the window.
So I took the mouse apart and found that it had little rollers inside, each roller had a small black disc with holes in it. An LED one one side and a photoreceptor on the other... I assume it worked by counting the flashes of light through the holes in the disc.
The plastic cover on the mouse must be semi transparent and when hit by the sun, the photoreceptor was giving weird readings. I covered the mouse in black tape and never had the problem again.