Using a Chronograph Indoors?

[Kramer Krazy]

I broke down and ordered a Shooting Chrony F-1 last week, and it arrived yesterday. I was hoping to use it tomorrow evening at the indoor range that I go to, so I can check some 45ACP and 38 Spl ammo that I have relaoded. The instructions say that flourescent lighting will often confuse the chrony, giving false readings, and they even offer a $35 light fixture to compensate for the fluttering of the flourescent lights, but I didn't buy the kit, nor can I get one by tomorrow. Looking at cost-effect options, can I simply hang a 100w flood light or trouble light over the chrony? What about attaching a flashlight of some type on top of each diffuser? Anyone have any other options that they have used and had work?

 

[Sport45]

I've never tried a chronograph indoors, but in theory, either should work. The light kit just places an incadescent tube (40w, maybe) over each skyscreen to illuminate them. The cronograph is looking for the bullet to block some of the light to each sensor as it passes. Every flourescent light in the room is flickering off 120 times per second as the AC voltage passes through zero. The flicker isn't obvious to us since the glow "lingers" a bit in the coating and being different distances from various lights blends the effect. The electronics are much more sensitive than our eyes and see this the same as it would a machine gun with a 120 round/sec cyclic rate. It's not hard to imagine it being confused.

Incadescent lights solve the problem because the filament is always hot producing an essentialy constant light.

 

[JNewell]

My experience: indoors with flourescents does not work at all. Haven't tried the obvious yet, though - motivation was low, mostly curiosity.

 

[The Bushmaster]

Hey Sport45..A bit off subject, but...We use flourescent lights in the shop to calibrate our strobe hand tachometers...If the tack aimed at the flourescent light reads 7200 rpm then the tach is calibrated...How does that equate to 120 "blinks" (flickers). I know that 7200 divided by 120 equals 60 which would be the hertz...Would that be the solution??? Which also means that the sine wave would be running across the line twice per cycle (hertz)...

 

[Savage.250]

Sport45
The light kit just places an incadescent tube (40w, maybe) over each skyscreen to illuminate them.

I would go with Sport45 on this one. I got one of the last 3 SkyScreen Oehler 35's on Midway in January but did not get any of the indoor lighted diffuers. They're $30 x 3 plus shipping from Oehler so I just made my own.

I used:
3x 40T8 120v 40W AC tubular incandecent bulb (or something similar)
$7.00 each
6x clips (Couldn't find the ones pictured so I found some clips that are
used to clamp brooms/shovles etc. in your garage.) $6 or $7
3x ordinary corded light buld sockets. $5 each

Just stuff from the local hardware store.
One is needed for each SkyScreen as Sport45 has mentioned. (Pic is off the Oehler site. It's of their lighted diffuser. As you can see it's mostly generic parts.)
Good Luck!

 

[MNgoldenbear]

The flicker isn't obvious to us since the glow "lingers" a bit in the coating and being different distances from various lights blends the effect.

Actually think it has more to do with your "persistence of vision". The coating material of a fluorescent tube emits pretty quickly. Seen a demo where the tube is moved rapidly. You see bright and dark regions where the tube was when it was "on" and "off" during the cycle. (Another neat demo of similar idea was an LED tester that lit green on one polarity, red on the other, and orange on AC. Spinning the tester while hooked to AC revealed that the "orange" was a series of red and green flashes that the eye blended together to make orange.)

Anyway, back to the actual topic. Yeah, the lighting source needs to be continuous, so it should be incandescent if used indoors. To give an idea of why, let's say you're shooting .22 LR and want to measure velocities to within 10 fps (which isn't great accuracy by some standards) using 3 ft between photogates. To tell the difference between 1080 fps and 1090 fps, the chrono has to resolve time-of-flight differences of about 0.00002 seconds. The flicker of the fluorescent is about every .008 seconds, about 400 times as long. Things get worse as the speeds get higher and screen separation gets narrower (and as you demand more accurate readings). Really random whether your equipment will miss the shot completely, see the bullet pass both gates, or only one or the other.

 

[Sport45]

Hey Sport45..A bit off subject, but...We use flourescent lights in the shop to calibrate our strobe hand tachometers...If the tack aimed at the flourescent light reads 7200 rpm then the tach is calibrated...How does that equate to 120 "blinks" (flickers). I know that 7200 divided by 120 equals 60 which would be the hertz...Would that be the solution??? Which also means that the sine wave would be running across the line twice per cycle (hertz)...

Exactly. AC voltage is a sin wave that starts at 0, ramps up to a maximum voltage (~+115V), drops through zero to a minimum (~-115V) and then returns to zero. Sixty times a second. The cycle repeats 60 times a second so you have 60 positive peaks, 60 negative peaks, and 120 zero values every second. 120*60=7200 blinks per minute. (Or 7200 flashes per minute depending on your point of view.)

 

[hpcc19]

Another issue

I have the Chrony light and it works indoors about 60% of the time. Lot's of ERR on the monitor.

I don't know about your indoor range though, but at mine the firing line is fixed and the targets are moveable. The Chrony seems to be severely affected by .45ACP muzzle blast*. With mine, you must be about 12' feet away from the Chrony when you shoot. I know my range wouldn't let me set up the Chrony 12' downrange, nor would they let me fire -12' back from the firing line.

Just my $.02

*it seems like the first sensor picks up the muzzle blast and the second sensor picks up the bullet, indicated speed is about 350 for a 750fps load, since the elapsed time is much longer.

 

[Kramer Krazy]

120w Flood Light Failed

Well, I took it to the range last night and it failed miserably. The range I go to has no problem with me removing the countertop in my lane and putting the chrony out a few feet from the firing line (it was 12'-15' from where I was shooting from). There was only one guy in there, my wife, and myself, so set-up was quick and easy. I placed a single 120w flood light above the chrony, but this didn't help. The chrony worked, but every reading was low......factory Winchester .357 mag 110 gr was reading 550-600 fps. I got a reading of 80.16 fps on a 38 Special reload. I shot factory 357 and two different 38 Spl reloads from a 4" Colt Python and two 45ACP reloads from a 3.5" barreled Colt Officers ACP. The manual states that low velocity readings are an issue with lighting...which is what I figured, so.....now I'm going to buy/build the lighting system for placing over the diffusers.

The manual also states that when using the indoor lighting kit, that you should turn off the overhead floursecent lights. I can't do this at the indoor range, but is is necessary? I figure if not anything else, I can rig up an umbrella over the chrony to prevent the floursecent lights from affecting the chrony readings as much. I wish I could shoot in my back yard, it would make testing loads a LOT easier.....I guess I just need to move out in the country.

 

[Kramer Krazy]

Figured I'd post an update.....

I bought the Chrony indoor light setup and went to the range last night. I started off with some 38 Spl reloads and they weren't reading correctly (84.6 to 214.8 fps). I couldn't turn off the flourescent lights overhead, so I threw a B-27 target over the Chrony.....still no help.......I was going to chaulk it up as being worthless indoors, but I switched to the 44 Mag. Surprisingly, it read every shot from the 44. I then switched over to the 45ACP, and it wouldn't read those, either. So, out of about 50 rounds, the chrono wouldn't read the 38/357 nor the 45ACP, but it did read the 44 magnum loads. I think I'll have to start making trips to the outdoor range to chrono future loads. :banghead:

 

[jmorris]

A year or so ago I was helping my brother in-law with a science project and I needed my chronograph to work one night. I used a 2’x3’ sheet of cardboard that had a white surface and rolled it in a circle and set the chronograph where the two over lapped then placed a right angle 7.2v flashlight facing up along side the chronograph. You don’t need the sky screens for the same reason you don’t need them on a cloudy day. It worked for us and was free.