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Both were Chrony's but different ages.[/quote]

Well, anything that happens must be possible. And now we have another example of one of the older Shooting Chronys going bananas. Hmmmm......

The fundamental system is extremely basic: A start pulse, a stop pulse, a count of the clock pulses in between, and a distance divided by measured time to get speed. Such a system either works right, or not at all. The only guess I can come up with is loss of hermetic seal on the oscillator unit, or some kind of internal contamination that slowly diffuses. I've never actually seen that happen.

So I am perplexed.[/quote]

Denton,

My first Shooting Chrony performed well, as far as I could confirm from shooting various loads (including the .22 rimfire used to test my first chronograph), and it was one of the early ones with cardboard "shades," as I mentioned previously purchased in the early 1990s.

Unfortunately it met its end around a decade later due to a misplaced .41 Magnum bullet. The two I had after that were the later models--which were the ones that declined in accuracy.

One of the things I learned from the Shooting Chrony folks during this period is that dust on the photo-sensors can cause problems, filtering in throgh the slots. Which is why I've placed transparent tape over the slots of every photo-electronic chronographs I've used since, including my Oehler. Tested that by, again, shooting the same ammo from the same rifle over the same chronograph. They all recorded the same velocities.

Well, anything that happens must be possible. And now we have another example of one of the older Shooting Chronys going bananas. Hmmmm......

The fundamental system is extremely basic: A start pulse, a stop pulse, a count of the clock pulses in between, and a distance divided by measured time to get speed. Such a system either works right, or not at all. The only guess I can come up with is loss of hermetic seal on the oscillator unit, or some kind of internal contamination that slowly diffuses. I've never actually seen that happen.

So I am perplexed.[/quote]

Denton,

My first Shooting Chrony performed well, as far as I could confirm from shooting various loads (including the .22 rimfire used to test my first chronograph), and it was one of the early ones with cardboard "shades," as I mentioned previously purchased in the early 1990s.

Unfortunately it met its end around a decade later due to a misplaced .41 Magnum bullet. The two I had after that were the later models--which were the ones that declined in accuracy.

One of the things I learned from the Shooting Chrony folks during this period is that dust on the photo-sensors can cause problems, filtering in throgh the slots. Which is why I've placed transparent tape over the slots of every photo-electronic chronographs I've used since, including my Oehler. Tested that by, again, shooting the same ammo from the same rifle over the same chronograph. They all recorded the same velocities.[/quote]

Thanks for the additional information.

Dust in the optical system sounds plausible. Another might be that the designer saved about $.40 per unit by using an inductor/capacitor oscillator rather than a crystal oscillator. You can get away with that at 4 MHz, where some models ran their clock, but not very well at 12 MHz where my particular model had its clock. But, like you, I sent my Shooting Chrony to a younger shooter and moved on to a newer design.

I suppose that I will die wondering....

John;
Good evening, I hope you all are well tonight.

Well once again I've learned something from you - thanks yet again.

What brand of transparent tape do you use? Do you replace it if it starts to yellow or age?

Without looking at it now, I'm assuming the Pro Chrono can benefit from that as well?

Our range is a dust bowl on a good day so this is likely pretty huge for chronograph accuracy and longevity.

Thanks so much again for sharing these little bits of wisdom with us, I very much appreciate it.

All the best.

Dwayne

Thanks Dwayne,

I have used the typical thin Scotch tape that comes in the palm-size plastic dispensers, but more recently have used their heavy-duty package tape, partly because it's a lot tougher and so far hasn't seemed to turn yellow. But also use it because we always have a pile on hand, since it's what Eileen uses when packaging the books we publish--and yep, I put it on ProChronos as well.

Good hunting,
john

Please don't put tape over the lenses of Oehler Skyscreen III units. While the little lens system might appear trivial, I spent almost a year on its design and did not include the effects of tape.

While I'm sure that others have encountered dusty sensors and may have solved the problems with tape, I recall only one instance where it caused a significant problem. Bruce Hodgdon reported trouble with the photoscreens in his test tunnel. When I stopped by for a visit, we removed the screen covers and found the insides coated with the firing residue from many rounds of Pyrodex and other dirty loads. A convenient air nozzle took care of the residue and operation returned to normal. Incidentally, the light slot did include a clear plastic cover; the junk found another way in.

That makes sense, Ken. I give the sensors a quick squirt of air that I keep with my camera. I presume it helps, as I have never had any problems with residue.

I confess that I did try the tape, but noticed a slight bit of crud on it. I assumed it was dust sticking to the underside.

Ken,

Have never applied tape to my 35P--but have found it helps with various "cheap" chronographs, especially in dusty Montana. As noted, got the suggestion from the Shooting Chrony folks....

Thanks,
John