Hi,
WIth regard to PI detectors,
There is the general belief that higher voltage break down, means faster discharge, and therefore sensitive to smaller targets.
I tried a MOSFET with much 'better' specs : lower resistance, faster turn on and turn off time, higher voltage breakdown (600V).
And it made the detector sensitive to wet sand, this is because an oscillation occurred (to shield, or ground or something) (see attached) I think.
With the standard mosfet: IRF2405, the detector is sooo quite and stable, even in wet sand, and in the water.
However, simply changing the mosfet, can turn it into a noisy piece of garbage.
Observations:
The high breakdown voltage, does not really improve the response to smaller targets, it simply means the discharge will be faster initially at the very start., but as soon as the threshold voltage is reached, i.e for most of the discharge, there will be a good rapid magnetic field change.
Even if the maximum flyback voltage is limited to 75 volts (by a diode), the detector can still be very sensitive to small targets.. intially the discharge is slow, and the voltage is greater than 75V, however when this point is reached, the change in magnetic field, is almost the same as with the higher voltage ...the delta-magfield has only been delayed.
The most important aspect of target sensitivity and fast discharge is COIL CAPACITANCE..
If anyone has any ideas what going on with the above curve, to make the detector sensitive to wet sand, let me know.
Note, with the standard mosfet, I can dig a hole in the sand under the water with the search coil, and it wont beep. (unless there is a target).
WIth regard to PI detectors,
There is the general belief that higher voltage break down, means faster discharge, and therefore sensitive to smaller targets.
I tried a MOSFET with much 'better' specs : lower resistance, faster turn on and turn off time, higher voltage breakdown (600V).
And it made the detector sensitive to wet sand, this is because an oscillation occurred (to shield, or ground or something) (see attached) I think.
With the standard mosfet: IRF2405, the detector is sooo quite and stable, even in wet sand, and in the water.
However, simply changing the mosfet, can turn it into a noisy piece of garbage.
Observations:
The high breakdown voltage, does not really improve the response to smaller targets, it simply means the discharge will be faster initially at the very start., but as soon as the threshold voltage is reached, i.e for most of the discharge, there will be a good rapid magnetic field change.
Even if the maximum flyback voltage is limited to 75 volts (by a diode), the detector can still be very sensitive to small targets.. intially the discharge is slow, and the voltage is greater than 75V, however when this point is reached, the change in magnetic field, is almost the same as with the higher voltage ...the delta-magfield has only been delayed.
The most important aspect of target sensitivity and fast discharge is COIL CAPACITANCE..
If anyone has any ideas what going on with the above curve, to make the detector sensitive to wet sand, let me know.
Note, with the standard mosfet, I can dig a hole in the sand under the water with the search coil, and it wont beep. (unless there is a target).
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