Mr Roboto,

The sensors are infrared in the Prochrono. I am not sure if that is the same chrono you are using. I use the IR light bars even when I am using my Prochrono outside and get good results until near dusk. You need diffused light. 2 kilowatts of light is a lot and may not be suitable for the chrono. Heck, you might melt the plastic or at least make he room very uncomfortable. You should be using a light bar if you are indoors (think about the response of the sensor as a function of frequency and amplitude of the light). I get errors when the light conditions are not right. I am guessing that one sensor picks it up and not the other. I have never had to mess with orientation to get rid of it. My guess is that it has to do with your light source and the fact that changing orientation fixes it, sometimes, is just a coincidence. I get none of the sensitivity to trajectory that you are seeing which leads me to believe that your light source is the problem. When I use my shooting machine I can nail the same number no matter where I stick the arrow though the measuring zone. I know that to be the case since my shooting machine walks. Also, I do not see that problem when I hand shoot.

 

Agreed, sounds like a light issue. Do you have the diffusers on?

 

Here is the light kit for your unit. The light kit makes a big difference. You are sure of getting the correct frequencies for the sensors.

http://www.shootingchrony.com/manual_ChronyLedLamp.htm

 

If you want to get accurate and consistent speed readings, I would agree with Hank. The light bar kit makes a world of a difference. I got one for my chrono and I stopped getting errant readings. I used to use CFL bulbs and I am quite certain those bulbs were the source of all my erroneous readings.

 

The light kit is designed for indoors but I use it most of the time. The only time I do not is if I am somewhere where I do not have power. Most of my chrono work is done outdoors at my house where I have power available. If I take it to an outdoor range I use the standard diffusers. I do a lot of measurements. Probably way more than the normal archer with all the bow testing I do. I get good consistent results.

 

The 20 ft/s reduction was very consistent when the arrow flight was 3 inches closer to the sensors. It was interesting that it was a consistent drop as opposed to a random fluctuation. I spent a lot of effort at trying to remove variability in arrow position and angle through the Chrony.

I will look into the Light Bar.

New question,

When I plot out arrow velocity as a function of arrow mass I get a fairly smooth decay in speed as the arrow mass increases. I was testing masses between 320 to 760 grains. Bow efficiency went up as the mass went up. Each string of data consisted of 10 shots.

Now I was getting a standard deviation of about 1.5 ft/s for each of the arrow mass tests.

Now for an average archer, would a 1.5 ft/s standard deviation fall into the normal range of a non-clicker shooting consistency, or is this considered high and that I have a lot of variability in the Chrony due to the lack of a light bar?

 

?? Were you using the diffusers? If not, do so it may take care of the problem.
If you were, then you probably have ambient light reflecting off the bottom of the arrows which would explain the discrepancy you were getting with the various heights above the sensors.
Taping cardboard side shields to the diffuser support rods may take care of that problem.
I never actually measured it but you will get some deviation with height and horizontal alignment (maybe on the order of 2 fps between 3" & 10" up, left and right) nothing near what you are seeing.
I would say 1.5 fps std dev would be in the realm of the average "good" shooter.

 

According to the instructions with my chrony, the bulbs need to be incandescent. They specifically state not to use fluorescent bulbs as they flicker. I made a light bar for mine using (2) 40 watt incandescent light bulbs over the top of the diffusers and have never had a problem. Have used this set up for 20 years.

I believe your problem is the halogen bulbs.

 

Instructions? what is that? The box came without any instructions. Might be why it was in the bargain section at Cabelas and sold "AS IS" no return.

I was told you have to have a lot of light and use the diffusers for indoors. So I have 1000W halogen lights near the Chrony, pointing straight up, and bouncing the light off the ceiling back down to top of the diffusers. I couldn't get any reading without the halogen lights in my garage.

I can try my trouble light. Its got a 100W incandescent lightbulb.

 

I think error is introduced if your arrows are not flying straight. I've had issues with poor releases either in the err1 or err2 errors or inconsistent speed readings. All the chrony knows is when the light sensors get tripped, not by which part of the arrow is tripping them. So if the tip trips the first one and then moves out of range the shaft may trip the second one later giving a false low reading. The opposite can happen too. The eer errors are when one or the other sensor is missed completely so you know this might be happening.

 

That is one of the things I have been wondering about. The width of the sensor window is about 1-1/2 wide. Where as the "V" shaped window is about a foot wide at the diffusers.

The way this unit appears to be working is that the arrow must fly between this very narrow "window" in order to get a reading. Its like most of the area under the diffuser can't be used to read the arrow velocity.

Is this the normal usable area for these chrono's?

 

Too much light , use cheap led flashlights from harbour freight (long ones the same kind of width as diffusers)directly on your diffusers make sure unit is level and your shot is level also, light has to come straight down not from below I think your confusing the unit.
The diffusers are preferable indoors on cloudy days you can do without them outdoors .

Chrony's can be temperamental I use em for precision air rifles oh and make sure your at least one arrow length away.

 

I shoot mine outdoors w/o the diffusers (too lazy) and found you have to shoot close to and right over the top of the sensors. The unit has to be level (parallel) with your arrow, not true level. I shoot mine at a slight downward angle so as to not have to put my target on blocks.

 

Mr. Roboto,

It is time to check your results with what I did awhile back with a shooting machine, to see if our data supports each other.

http://tradtalk.com/forums/showthread.php?t=50984

http://tradtalk.com/forums/showthread.php?t=50972

http://tradtalk.com/forums/showthread.php?t=51222 This one should have said GPP and not grains/inch

 

Thanks for the link to the manual, but my chronograph is the Chrony F1.

One of the things that I want to do with this is measure that arrow velocity at the target at various distances. Need that to calculate coefficients of draw on the arrow. But I am getting concerned that if my model has such a narrow window, that I many not be able to do this even past 20 yards.