Open Loop Pulse Triggering
Results
Coil C
Again
we can determine the wire and coil current densities using the dry firing curve
of fig 1. Coil C data indicates that
the wire diameter is 1.25mm so with a maximum current of 103A, we have a wire
current density of 83.9Amm^{2} and a coil current density of 65.9Amm^{2}.
Note the increase in current density over coils A and B.
FIg
1. Coil current during dry firing
Fig
2. Projectile interaction with coil
Fig
3. Solid projectile No.1 speed and energy data
Fig
4. 4mm cored projectile speed and energy data
Fig
5. 6mm cored projectile speed and energy data
Fig
6. Projectile speed comparison
Coil
Efficiency
Again
we can show the efficiency of the coils at the peak projectile speeds, the data
is tabluated below.
Projectile 
Peak Power (W)

Conduction Loss (mJ)

Commutating Loss (mJ)

Total Loss (mJ)

Kinetic Energy (mJ)

Efficiency (%)

Solid No.1 
2.450E+3 +/ 5.0E+1

1.5742E+4

1.343E+3

1.7085E+4

7.04E+2 +/ 1.5E+1

3.96E+0 +/ 9E2

4mm Cored No.1 
2.450E+3 +/ 5.0E+1

1.4681E+4

1.409E+3

1.6090E+4

6.52E+2 +/ 1.5E+1

3.89E+0 +/ 9E2

6mm Cored No.1 
2.450E+3 +/ 5.0E+1

1.3342E+4

1.458E+3

1.4800E+4

5.42E+2 +/ 1.5E+1

3.53E+0 +/ 1.0E1

Table
1. Energy and efficiency data
The
peak power dissipation is getting quite large now, it's about three times that
of coil A. The efficiency value of 6mm cored projectile No.1 looks a little out
of place being noticably smaller than the others. I don't know if this is significant.
I should really plot the efficiency curves for the projectiles but it takes ages
to cut and paste the raw DSO data into the spreadsheet, process it, get the curve
fits, and finally integrate them to get the energy dissipated. It's possible to
do the integrations in Matlab using the numerical trapezium function. There are
lots of data points in the DSO files so the trapezium approximation gives
quite accurate results compared to the analytical integral solution obtained from
the fitted curve.
