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In Reply to: RE: SL-12XX strobe AC or DC powered? posted by Bry on September 01, 2014 at 07:44:40
A neon is a form of gas discharge tube which doesn't fade in, it fires quite quickly once the threshold voltage is reached. If set up correctly it will give a very crisp strobe.
Mark Kelly
Follow Ups:
Ah, well the AC driven neon strobes I've seen have had some kind of smearing effect. Maybe it's because they stay on too long.
I don't know what causes that but it shouldn't happen: the Pearson Anson relaxation oscillator works using repeated triggering of a standard neon and they're usually OK to about 20 kHz, so the on /off time for a neon has to be less than 50 microseconds. You shouldn't be able to see that transition.That being said the transition time for a standard* LED is in the nanoseconds so they are the device of choice these days.
* Not white ones, they use a phosphor.
Mark Kelly
Edits: 09/01/14
But at 60Hz the on-time will be much longer. If the threshold is ~60V, the bulb will turn on at ~20° into the half cycle and turn off at ~160°. At 60Hz, the on duration will be ~6.5mS. The edge of a 12" platter will move ~.136" in that time.
The LED method undoubtedly uses a square wave with a low on-time duty cycle to create a crisp display.
Does the neon bulb intensity vary with current between the on threshold and off threshold?
There must be a German word for that which is retropectively obvious.
If I knew it, I'd use it now: I hadn't considered the movement of the platter even though that's what we are trying to measure.
Thanks.
Mark Kelly
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