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 Post subject: Chronographs
PostPosted: Fri Jul 05, 2019 6:07 am 
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Lieutenant Colonel
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Joined: Tue Apr 06, 2010 4:17 am
Posts: 1793
Location: Whitemouth R., up the Escarpment
This seems the likely spot for Chronograph info.

As of late, I've been seeing a bit of misdirection and, or, plain old lack of knowledge on chronographs and their use on just about every board I read.

I guess the most important thing is that these machines are designed to read against their diffusers, and not the light source. The light source is to illuminate the diffusers, so's the sensor can pick up the interruption in the light against the diffuser.

For most of us shooting indoors, artificial light can create problems. Fluorescents pulse, and that interferes with the way the sensors output data. There are a couple of ways around this. Good old incandescent lamps are about the easiest, and most straight forward solution. I simply suspend a 100 W bulb between 8" and 18" above the center of the diffusers, and let fly. I get readings consistent with normal outdoor daylight this way.

If an absolute need to go to L.E.D. lighting is present, battery operated units are pulseless. They should illuminate the diffusers from above. I see a lot of l.e.d. units suspended below the diffusers~ which can lead to false readings. Normal household current pulses at 60 cycles, and will add a pulse to a plug-in style l.e.d. lamp.

Batteries. I have gotten the most consistent, and long term performance from good old copper top. In my F-1 chrony, a new one lasts about 2 years. A new one outputs between 9.6 v and 9.8 v. I find the F-1 starts giving repeated error readings when the battery drains to around 8.8 v. to 8.9 v.

I shoot from 12" to 18" away from the primary sensor with my air guns and .22's. For center fire, I use a minimum of 2 feet away from the primary sensor. This prevents gas, powder, flash, and oil (from air guns) from interfering with the sensors.

Hope this makes some sense. Just trying to prevent a bit of grief for those new to the chronograph idea. Now that I think about, my chrony has become indispensable...

Regards,

Doc Sharptail

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 Post subject: Re: Chronographs
PostPosted: Fri Jul 05, 2019 5:59 pm 
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Major
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Joined: Sat Aug 04, 2007 3:40 pm
Posts: 1091
Location: Georgia
I did not think about the ac powered leds. I probably would have checked some if I had an oscilloscope. I used to know human flicker fusion threshold and I thought it was about 24 flashes per second. Naturally the semiconductors are much faster and some can switch on in nanoseconds.


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