Hi again,
I think that the supply voltage, coil and power supply circuitry can be dimensioned to begin with as you say.
First some basics in short:
The maximum current that can be drawn through the coil is mainly dependant on two things, the voltage that is applied to the coil and the winding's resistance.
The coil's resistance depends on the wire's resistivity, the total length of the wire in the coil and the wire thickness.
The magnetic field occuring is mainly dependant on the current through the coil and the number of turns, the physical size of the coil has also influence.
When applying voltage to a coil, the current will rise linearily with time until the maximum current (=voltage/resistance) is reached.
The time to reach the maximum current depends on the inductance of the coil, in turn depending on the number of turns and the coil's "form factor" (thickness/dia).
Thus, it is no point keeping the pulse length longer than this time, all excess power will be waisted and the impulse will also be weakened.
The influence on an object to be found is depending on a lot of stuff, but mainly the distance to the coil and the angle to the coil's center line, simply put.
This influence gives reason to a field emitted from the object when the exciting field disappears.
This emitted field can be picked up by the same coil, or better another coil placed a little offset from the transmitting coil.
The waweform and amplitude of this signal tells much about the material, size and other things on the object, and also the distance/angle to it.
Then, the power supply must be able to cope with this special case of load (short pulse, high current), but the mean (over time) power to the coil depends on the pulse length in relation to the pulse repetition rate.
All other supply currents must of course be added to this to find the power supplie's requirements.
The battery voltage must be selected depending on all previous parameters, or be set to a value and used as parameters in the earlier calculations (which I would do).
Also, as you may see, higher voltage gives possibility to a high coil current ,which not necessarily is a great advantage in overall performance.
It is ,as you might see, important to break down the design in small blocks that can be handled.
Hopefully this will help you and others, I can assist some in the calculations but my time is limited right now because of a rough load at work.
If I missed or mixed something up, I can only refer to my age combined with little time to spend.
Best wishes!
Linkback: You are not allowed to view links.
Please Register or Login
http://www.thunting.com/smf/index.php/topic,60153.msg295413.html#msg295413
|
|
Logged
|
|
