How to calculate coil induction.

[Dest]

For my project I using 2 Rx and 1 Tx coil.
Rx coils are in induction balance to exclude ground efect, but I thing they are not calculate properly.

[cheurfi habib]

reequestb

For my project I using 2 Rx and 1 Tx coil.
Rx coils are in induction balance to exclude ground efect, but I thing they are not calculate properly.

hello my friend
I ask my friend. if it can help me to make a coil very sensitive to a depth ideal for detectetion objects
I notified that I make tezoro Aldorado
thank you answer me in the short time

[mikebg]

I guess you use the shown below loop configuration. Each RX winding is placed in induction balance with TX coil. In theory, the mutual inductance M between RX windings is positive and L2 = L2A + L2B +2M. In practice, the M is relatively small, that's why we calculate approximately inductance of each RX winding as L2A = L2B = 0.5L2, where L2 is calculated for resonance with C2.
Calculation of inductances L1 and L2 depends on detector type: narrow band (VLF) or wide band (PI) metal detector.

PI
For wide band MD there are no capacitors C1 and C2, however these capacitances exist in the equivalent network. They are stray capacitances formed mainly by shielding and cables connecting coils to control box. To achieve "fast network", the inductances L1 and L2 are calculated for resonance with stray capacitances at frequency more than 100kHz.

VLF
For TX efficiency of narrow band MD we should use large capacitance C1, for example 1uF. For phase stability of RX tank circuit, we should connect C2 having capacitance more than stray capacitance, for example 2200pF. Then at given operating frequency, C1 and C2 we can calculate L1 and L2. In old search head designs of White's, the RX tank resonates at lower frequency than TX tank because capacitance of C2 is increased.