Post by: klugesmith on September 27, 2020, 07:08:06 PM
with no "other" that might get, for example, work with microsecond flashlamps.
For little scientific videos I sometimes turn to compact digital camera, mostly idle since starter smartphone arrived.
Still pictures from smartphone often show artifacts of progressive "shutter" when subject is, say, a neon light.
Cheap smartphone's picture and video modes have even fewer control knobs than the point and shoot cam (Coolpix 550).
I wanted to measure the speed of an induction motor from a scrapped vacuum pump.
Nominally 1/4 HP, 3450 RPM, but probably more like 3580 RPM with no load.
It's neat that slip rate of 20 RPM (1/3 Hz) can induce enough rotor current to overcome bearing and windage drag. Will motor turn even faster with cooling fan ports blocked, as do vacuum cleaners when hose is blocked?
Old-fashioned fluorescent lighting didn't give enough stroboscope contrast to be useful.
My power-line-synchronous LED stroboscope is buried in clutter.
Got useful strobe result with a xenon-arc lamp, powered by a NST. Circuit dynamics apparently result in a brief, bright spark once each half cycle. There's substantial but tolerable jitter in time, arc path, and intensity.
Second picture is snipped from one frame of video with CP550. Better production values, and numerical results, to follow.
Here's an old video made with the LED stroboscope:
https://www.flickr.com/photos/r_k_f/3688448113/
Post by: klugesmith on September 28, 2020, 08:16:46 AM
One from a lot of about 20, I think 20 kV 30 mA, bought long ago.
Tonight I had much better results with a microwave oven diode, even though it's not technically rated for NST end-to-end peak voltage. The more pointy lamp electrode was taken to be the cathode. Eye protection was in place. With or without diode, lamp didn't light until NST primary voltage was above 50% of nominal. For this picture the NST was at about 70%, and the apparent phase of light pulse jittered by up to 10% of cycle period.
Slip rate of the motor was about 10 RPM, and decreased to about 9 RPM when I blocked fan air inlet with my hand.
I tried several other lamps with the diode in series: a curly CFL tube, a curly xenon photoflash lamp, and a mercury-arc lamp with a 9-pin minature base!
In those cases the stroboscopic view showed a blurry, very low contrast bright area on one side of motor coupler. Not well suited to measuring apparent rotation rate. Bet we could do better with variac, low voltage transformer, and simple white LED (how about a white and a blue in antiparallel configuration?) The missing stroboscope energizes LED string, via a transistor, with short pulse from a 555 that's phase locked to AC power cycle.
Post by: Zipdox on September 28, 2020, 09:09:45 AM
Post by: plasma on September 28, 2020, 09:15:09 AM
Just some info.
Post by: TMaxElectronics on September 28, 2020, 10:50:31 AM
Might even be able to capture some larger things with it, as the LED could probably to 500W peak when pulsed slowly enough.
If I find the time I'll make up a board with a BNC input for control from a signal generator and try it out :)
Post by: klugesmith on September 28, 2020, 05:14:51 PM
Good point about the peculiar OSRAM bulb maybe being an intentional radiator of ultraviolet light. Label says Spektrallampe.
By the way, regarding eye safety around UVC-emitting things like mercury vapor rectifiers and germicidal lamps.
It makes no difference whether you avoid looking at the lamp.
The geometry that matters is whether the lamp can see your eyes.
254 nm doesn't even penetrate the cornea, much less get focused to a spot on the retina.
There are cases where you can get a good look at the glow, without receiving a hazardous exposure. Protective equipment like real glass glasses or goggles can't hurt.
Post by: Zipdox on September 28, 2020, 06:41:56 PM
Post by: klugesmith on September 28, 2020, 07:36:45 PM
Didn't intend to suggest a cavalier disregard of UVC hazards. As with many toxicological risks, it's best to just stay away if you don't have time to learn the numbers and measure exposure with instruments. UVC is not found in natural sunlight, on Earth, but has been very well studied regarding human health. It's not as sneaky as x-rays made on purpose, or radioisotopes.
Zipdox, have you noticed the recent debate about "deep UVC" excimer lamps?
Their developers claim that 222 nm kills germs while being much less injurious to people, compared to 254 nm, which has represented UVC for most of a century. There are studies, sponsored by makers of traditional 254 nm equipment, that warn "not so fast!".
Post by: Zipdox on September 28, 2020, 08:49:09 PM