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  #11  
Old 01-04-2011, 12:38 AM
mousegun mousegun is offline
 
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Page 251 of Hatcher's Notebook (1947) mentions a Le Boulongé chronograph.

The chronometer is a precision device to measure absolute time with reference to traceable standards. In the era of celestial navigation chronometers with precision movements were built as transfer standards and were periodically calibrated with solar and planetary observation and rated for drift. Consistent drift rate was more important than intrinsic accuracy. Later, electromechanical and piezoelectric standards were used finally culminating in atomic references directly driving chronometric movements. In other words, it's a clock.

The chronograph is a device to record time intervals. A chronograph usually has some form of relative chronometer or timer in it. This is not always the case, such as interval recorders using spark discharge to record motion or periodicity, but generally speaking some form of time interval logging is involved -- usually presented in the form of inverse period (velocity). In other words, a chronograph is a log.

Chronographs have been called chronographs since I can recall interest in them. I've never heard of a device with this specific function called anything else. Doesn't mean it hasn't, just that in almost 50 years I haven't heard it.

Is this important? Probably not. It's just words. With meaning.
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  #12  
Old 01-05-2011, 11:44 PM
Unclenick Unclenick is offline
 
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The Boulangé chronograph is a 19th century electromechanical apparatus that uses a breakwire screen to open connections to solenoids. The first breakwire would cause a zinc rod to drop, while the second breakwire would release a spring-loaded striker that put a ding in the rod at whatever distance it had dropped to. Like its contemporary, the Bashforth chronograph, which traced a line on graph paper on a fast rotating drum during the interval between two wire breaks, this resulted in a graphical representation of time. Hence "chronograph" or literally "time drawing".

The modern direct reading bullet speed meters (what they really are) revived the use of the term, but not with the original meaning. The readout is a graph in the sense that writing is a graph, as in graphology. But it doesn't display time, so I think it's a poorly chosen term for the modern devices. Bullet speed meter just isn't sexy enough, I suppose, even if it's more accurately descriptive.

The early digital ballistic chronographs were built with vacuum tube logic for counting a crystal time base. The crystals were ultimately traceable to the old Bureau of Standards. I don't know the details of the proximity sensing coil system that was developed between the wars for use in place of breakwires as part of a portable system. I only know that, like the electromechanical devices from the 19th century, its response was slow. Without digital logic, the analog instruments need to make a big enough trace or meter movement to resolve small bits of time. That's why the first screen (wire or coil) was at 6 feet and the second was way out at 150 feet, for an average of 78 feet. That's where the military 78 foot rifle velocity measuring distance came from.
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Last edited by Unclenick; 07-13-2011 at 12:55 PM. Reason: typo fix
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  #13  
Old 01-06-2011, 03:38 AM
mousegun mousegun is offline
 
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Great info. Thanks. I wondered just how the Boulangé worked since I haven't encountered one. Just read about its use in Hatcher's book

Had some experience in freshman physics with waxed recording paper on disks and drums using spark discharge. Painful, but clever. Later I worked with gated decade counters with high stability piezo oscillators traced to WWVB with a phase metering receiver. Since '94 I've been working with atomic clocks (rubidium mostly) in simulcast trunking systems, but these have recently been replaced with GPS receivers. Time lurches on.

Tried making a crude chronograph - speed meter - back in the early 70s with a gated counter, but making reliable screens was such a hassle I gave up.

All good stuff.

Insofar as the "bullet speed meter" term is concerned it's probably correct. But since the readout of a "chronograph" in this sense is a simple function of inverse frequency (period) and displacement, it's really an interval recorder rather than a time indicator. I think "chronograph" isn't too far off the mark.
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  #14  
Old 01-06-2011, 02:31 PM
Unclenick Unclenick is offline
 
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No, it's not way off. You know a time base is in there somewhere. But the readout is bullet speed, not time or time intervals. That's why I think of it as a speed meter.

I did build and sell a few breakwire ballistic stop watches at gunshows back in the early 80's. Also messed with, but never sold (too much trouble) a conductive ink pattern silk-screened onto paper to replace the wire. They and the wires were on a PVC pipe frame that set the spacing. Slow work and some bother, but it functioned OK. 4 MHz crystal time base, just as is commonly used today, chosen based on the counter chip's limitations. I've still got one in the basement somewhere. I should probably take a photo to show how technology has advanced.
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  #15  
Old 01-06-2011, 07:59 PM
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Well, I can disagree with you, but you're not wrong.

There was a chronograph speed-meter in the '70s with a printed grid on paper. I thought it might have been a good system but the cost of a pad of traps was more than I could justify and the thought of replacing the traps after every two or three rounds wasn't encouraging. Also, I had my doubts that the distance would hold constant after fiddling with it every few rounds. Had to wait another 25 years...

Enter the Chrony F1 Master. Soon's I got it one modified it to access the additional firmware features. Been pretty effective, but you get what you pay for. Helps to have a black Sharpie for the bullets. Darkened projectiles make it more sensitive.

Time flies when you're having fun.
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  #16  
Old 01-07-2011, 03:18 PM
Unclenick Unclenick is offline
 
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That's why I gave up on the silk screen. Too costly per shot. Later I thought I should have rigged some opposing one-sided clips and reversed the trip from break to make and told people to spray glue foil on both sides of some shirt cardboard and let them use that. If you peel back any foil that bridges one side to the other, the same screen can be used again by aiming a little to the side.

IIRC, Radio Electronics or Popular Electronics published a design in the late 60's or early 70's that counted with individual light bulbs for each number of each digit. Columns of lights. Then when the first decoder/driver chips for Nixie tubes showed up and the design was redone for those. All chronometers (time meters), though. No math being done for fps.

Early 4 bit programmable microprocessors became available that could have been used in that sort of application sometime around the mid-70's. Even a calculator chip could have been adapted, I think. So it could be done. The issue was still cost, though. Even by the time I made my breakwire chronometer it was still cheaper to use a counter chip and LED readout than to mess with most micro's. Retailing at about $50, mine was mainly a cost beater.
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  #17  
Old 01-07-2011, 06:45 PM
mousegun mousegun is offline
 
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Quote:
Originally Posted by Unclenick View Post
That's why I gave up on the silk screen. Too costly per shot. Later I thought I should have rigged some opposing one-sided clips and reversed the trip from break to make and told people to spray glue foil on both sides of some shirt cardboard and let them use that. If you peel back any foil that bridges one side to the other, the same screen can be used again by aiming a little to the side.
Though about doing that with foil/paper sandwich but ran into the fragility problem of trying to keep a usefully large foil trap clamped in suspension on a windy day and still have enough reliability to be useful.
Quote:
IIRC, Radio Electronics or Popular Electronics published a design in the late 60's or early 70's that counted with individual light bulbs for each number of each digit. Columns of lights. Then when the first decoder/driver chips for Nixie tubes showed up and the design was redone for those. All chronometers (time meters), though. No math being done for fps.
The math issue is trivial for a personal instrument - just haul out the trusty HP45 and do the work. In a product that would be a show stopper.
Quote:
Early 4 bit programmable microprocessors became available that could have been used in that sort of application sometime around the mid-70's. Even a calculator chip could have been adapted, I think. So it could be done. The issue was still cost, though. Even by the time I made my breakwire chronometer it was still cheaper to use a counter chip and LED readout than to mess with most micro's. Retailing at about $50, mine was mainly a cost beater.
Until the Zilog chips came out it was pretty pricey and time consuming to do any kind of controller based I/O at that time, not to mention everything would be in assembler. Kinda hard to justify for a one-off hobby item. Also had lots of fun trying to find the magic words to cool the noisy bus problem. By that time I up to my hips in trying to keep a business afloat.

So.. time marches on.
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  #18  
Old 01-19-2011, 06:59 PM
1776 rebel 1776 rebel is offline
 
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As I study history I am sometimes amazed at what folks hundreds of years ago, in a pre-technological age achieved. Well the earliest velocity calculators I am aware of are called ballistic pendulums. You basically shot and hit a pendulum. From the pendulums movement on impact you can work backwards and figure out a number of things about the round. This wiki article is a nice treatment:

http://en.wikipedia.org/wiki/Ballistic_pendulum

Personally I saved up for years to buy an Oehler 35P. Then they stopped making it. Last year at the NRA meeting they announced they were starting up the line again. I got on the list and in October received shipment. I love it.
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  #19  
Old 01-19-2011, 08:46 PM
mousegun mousegun is offline
 
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Quote:
Originally Posted by 1776 rebel View Post
As I study history I am sometimes amazed at what folks hundreds of years ago, in a pre-technological age achieved. Well the earliest velocity calculators I am aware of are called ballistic pendulums. You basically shot and hit a pendulum. From the pendulums movement on impact you can work backwards and figure out a number of things about the round. This wiki article is a nice treatment:

http://en.wikipedia.org/wiki/Ballistic_pendulum

Personally I saved up for years to buy an Oehler 35P. Then they stopped making it. Last year at the NRA meeting they announced they were starting up the line again. I got on the list and in October received shipment. I love it.
Man, I am really glad to see that!
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  #20  
Old 07-11-2011, 12:23 AM
GGaskill GGaskill is offline
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I used a chronograph in the middle '60's that used printed foil screens for start and stop. The screens were good for only one shot which meant you really needed a private shooting area, and expensive, too. The read out was time in milliseconds (max of 999) as I recall and required measuring the spacing and setting it to a value that would allow a near full reading to accumulate but not go over (first time I tried it, we were getting velocities of 40,000 ft/sec from an air rifle; turned out we were wrapping the counter without realizing that.)

Last edited by GGaskill; 07-12-2011 at 10:48 PM.
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