PI coil design

[Anonymous]

Good day gentlemen, Question :- When winding coils for PI is there a particular proved method for ensuring maximum flux linkage between coil turn? It does seem possible that the bunching of the turns associated with the usual DIY method does not maximise the flux linkage between the windings and a better way would be to produce a layer coil winding. Any views on this, or nints & tips on how to get the best of coil designs?

 

[Anonymous]

 

[Anonymous]

Hi Steve,
The difference between a neat layer wound coil and a bunch wound coil would be very small as far as the flux linking goes and I doubt that it would have any significance in practice. What may be significantly different, however, is the winding capacitance, which wants to be kept as low as possible. The winding capacitance, in parallel with the cable capacitance, determines the natural resonant frequency of the coil circuit. Although the coil in a PI is not tuned, this natural resonant frequency determines the damping that needs to be applied to reduce the transmitter field as quickly as possible. This in turn affects the minimum delay time that can be used and the detectors sensitivity to small objects. Printed coils take this a step further in that the coil capacitance is further reduced by the gap between tracks.
Eric.