Chronograph Fundies

[TAT2D]

Fundamentals of Chronographs?

I've been looking at the chronographs in the Midway catalog wondering, "Just how do those actually work?"

What's the actual 'theory of operation'? Does anyone know? It looks like a pair of 'sensor's spaced some distance (several inches) apart, but how do they sense the passage of the round? They look like inductive loops, but is there enough ferrous metal in the bullet to make 'em react? Is it some other principal, completely?

Inquiring minds, and all that...

Also, I find it kind of funny just how *similar* most of the different brands/designs look. (The sincerest form of flattery.)

MrB

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[NoAim]

They are optical.

Bullet passes over 2 sensors at a known distance apart. Thus, if you know the time difference and the distance you have a speed.

The sensors look for the shadow of the bullet.

The "loops" you are seeing are merely sunshades. If it's too sunny out, the sensors can't pick the shadow of the bullet out of the brightness. The shades provide a light, but not super-bright background instead. Most shooters typically use them as a guide to keep the bullets over the two sensors.

 

[ZeroRing]

And because they are optical, be aware that they may have problems if they are not placed under clear sky.

It's for that reason that I added the indoor lighting kit to mine. The "sun shades" are replaced by a powered LED light bar which provides the "light" necessary for the sensors to detect the shadow of the projectile passing overhead.

Worrying about overhead trees, cloudy days, or covered range shelters affecting the function of the sensors are now avoided.