Pact Skyscreen Material

[Milanodan]

I have an old (orig?) Pact chronograph but haven't got any skyscreens. Haven't used it for years, but as I recall I rigged up some homemade skyscreens for it, and it read the speeds about 75% of the time.

Tried it today in my backyard with a .177 air rifle (no skyscreens at all), and didn't get one reading in about 10 shots. Looks like I'll have to make some new skyscreens, so what material works well? Some kind of translucent plastic?

As I recall, it always did much better on cloudy days than on bright sun/blue sky days.

HELP!

[jhrosier]

If you need some transluscent plastic for your screens, try cutting a chunk from the side of a milk bottle.

Jack

[Milanodan]

Ah, didn't think of that. Thanks. I'll try it tomorrow.

[WildmanJack]

Milanodan,
you may have to put two pieces of milk carton together to reach the ends of the upright rods. That ought to be pretty easy with one of those butane lighter torches. I used to use old milk cartons to repair holes in my kayak. Just melt and seal!!!LOL Goood luck..
jack

[AZ-Stew]

Just an FYI...

When electronic chronographs first came on the scene, they used "screens" that were kind of like printed circuit board material, but far thinner, with two layers, each containing part of the circuit traces that were used to trigger the counter in the electronic module. Since the bullet had to penetrate two screens to trigger the "start" and "stop" signals to the calculator, it was nearly impossible to both chronograph and shoot for group with the same string of fire because passing through the screens disturbed the flight of the bullet. In addition, the screens had to be changed after each shot because the start and stop signals were caused by breaking the metallic traces on the screens. One shot and they're gone.

When Oehler came up with the original "Sky Screens", the days of replaceable screens were over, and we were able to shoot for group with the same rounds we fired for speed measurement, because the "screens" were photo sensors set up to catch the shadows of the bullets as they passed overhead, rather than breakable barriers that had to be shot through to trigger the timer.

Point is, the "Sky Screens" are the electronic photo sensors, while what you're asking about are "sun shades", used to prevent false triggering caused by sunlight glinting off the bullets. The "sun shades" trick the "sky screens" into thinking you're always shooting under overcast skys, thereby prevent false triggering. This system works reasonably well, depending on the direction (compass) you're shooting and the hour of the day.

Regards,

Stew

[Milanodan]

I don't think "sun glint" was the problem today--the air rifle pellets are very dark gray and don't reflect much light at all. I guess the best lighting condition would be having the sun directly overhead while using the milk bottle plastic?

[hemiallen]

The skyscreen shade material isn't important, cardboard, etc will work fine. Try painting a pellet with an ink pen, ie felt tipped pen. Every time the conditions are incorrect and I get false or no read errors, painting the bullets black solved the problem.

Overcast days are best, or early or late when the sun is low....

Hope this helps
Allen

[454PB]

Those original screens AZ-Stew mentioned were relatively expensive, since the conductive "ink" was made of silver. As I recall, it was about 30 cents for each shot. This was back in the days when moulds cost $15, and gas checks were $5 per thousand. I began making my own screens using very small gauge wire removed from small electric motor windings. I'd wrap the wire around a cardboard strip about 2" tall and 4" long, then connect the leads to the wire ends. The reading was not direct readout like we enjoy today, but a binary code that had to be translated to feet per second using a tarage table. Just measuring one shot took about 5 minutes to set up. Man I love my skyscreens!

[Milanodan]

I'd love them too if they'd give me info.

Wonder what kind of lighting I'd need to use them indoors. I know fluorescent lights are a no-no.

[hemiallen]

The skyscreens, which btw I have several extra's for sale..lol ( no shades included), are optical sensors. I think you should contact Dr Oehler at his website......

Maybe even ask if he has any of the diffusers for sale seperate from the skyscreens....

I usually bring the bb gun with me to verify they are working, ie all the plugs are installed correctly, etc. Don't want to miss a bullet when shooting a group.

Good luck

Allen

[AZ-Stew]

Direct sunlight hitting the bullet at an angle (dependent on the direction of the sun) will cause glint and false triggering of the sensors. A clear blue sky will cause problems, as well, but I can't remember exactly what Dr. Oehler said about it in an article by him that I read regarding the potential inaccuracies of using light sensors as bullet detectors. The article was in Shooting Times about a year and a half ago.

The sun shades provide a uniform background for the sensors to "see", and when that uniform background is disturbed by the bullet, the timer is triggered.

454PB filled in some additional background info for you, and is correct about the early readouts. My chrono use doesn't go back quite that far, but I remember the earliest one I used required a couple of the big square 6V lantern batteries with the coil terminals on top. You were lucky to get a couple of hours of use from them because of the high current drain of the early ICs in the chrono. This made it expensive to run, even with "sky screens". I took the cover off once to see what was inside (it was the club's machine) and I'll tell you, there must have been a hundred 14 and 16 pin DIPs in there. Today's chronos use a single custom IC built on CMOS technology that will run for several days of shooting on a single 9V transistor battery.

Regards,

Stew

[fourarmed]

Another good source of material for diffusers can be found in any housewares department. It is the flexible plastic cutting boards. Flat, reasonably cheap, and plenty big enough. I built a box to set over my Pact sensor bar on clear sunny days. (I set the bar on an old hospital patient table instead of a tripod. Much easier to get aligned.) It has a window above each sky screen that is covered with one of the cutting boards. Hasn't missed seeing a bullet since.

[Crooked Creek]

The 60 cycle "flickering" of the lighting, that you don't see but the chrono does, is what I understand to be the problem with using chrono's indoors with artificial lighting. I've seen screens advertised that will work indoors, check with your unit's manufacturer.

[MtGun44]

The flickering at 60 cycle is only an issue with flourescent lights. I have
done chronoing indoors many, many times, but you must have incandescent
lighting.

You should be OK with no background, but it won't hurt. Make sure you are
shooting directly above the slots so the sensor can "see" the pellet, too
close is bad, too far is bad. Try for about 4-6" above the sensors, and you need
to be REALLY certain you are shooting over them. I use visual guides on either
edge (wire pins) of the skyscreens and align this so I am looking at a target
over them. Then shoot at the target so the pins are aligned on either side
from your benchrest position.

Bill

[Milanodan]

Didn't get a chance to make the sunshades yet, but I did a few "experiments" trying to get this Pact to indicate something. I set it up in a dark room, and swung a strong flashlight beam from the start skyscreen to the stop one, as fast as I could swing the beam. No response.

Then I turned on a bright overhead incanden. light fixture, and rapidly swung a few items over them--fast enough to whooosh like a baseball bat. Nothing.

Not having the instructions any longer, I tried pushing both red buttons on the front, and the display read "chronograph running". No help, still no speed readings.

Getting fed up with this Pact--must have a defect somewhere inside. Guess I'll be looking for one of the newer CED's/whatever.

[fourarmed]

If you think it is really dead, call PACT. When my first one - an original PC - went bad, I called them. The guy said "Send it in with five bucks." Couple of weeks later I got a refurbed Model One with upgraded skyscreens in the mail. Can't do much better than that.

[Milanodan]

Update

Found a new pair of skyscreens that I had ordered years ago. Thinking that my stick-swinging might be too slow to register, I taped the pair together such that the slits were 3/4" apart.

Put them outside late in the day, and I got readings every time I swung the stick--a 30" piece of 3/4" gray plastic conduit. After correcting for the close spacing, I could only manage ~60 MPH (~85 FPS). Then I removed the original skyscreens and tried them together, and got the same readings. It even worked indoors with an overhead light shining directly down into the skyscreens.

Took the new screens out to my favorite shooting place, and got readings EVERY shot-cast and jacketed. Total of ~50 shots. This time I sent the bullets a little higher than I used to--~5-6" above the screens.