Resolve measurement of I1, I2 and I12 into Ic and Id

This calculator takes values of the magnitude of I1, I2 and I12 (being I1+I2) and resolves it into its common mode (Ic) and differential (Id) components.

Measure:

• I₁, the current in one conductor;
• I₂, the current in the other conductor;
• I₁₂, the current with both conductors passing through the sensing core.

Note that I₁₂ must not be greater than I₁+I₂, if it is, then the measurements are in error.

The above form allows calculation of I_c  (the common mode component of current), I_d (the differential mode component of current), θ_dc (the magnitude of phase difference of I_d wrt I_c, θ_1-2 (the magnitude of phase difference of I₂ wrt I₁). (The instrument does of course directly read Ic as I_1-2.)

Note that external fields are principally due to 2I_c (or measured I₁₂).

The calculator tries to use the number entered, negative numbers will be changed to positive, missing data 0, NaN means Not A Number (correct the input if needed), results will not be calculated when I₁₂ > I₁+I₂.

CMR (common mode reduction) (or CMRR for some) is the the magnitude of the ratio of differential current to common mode current expressed in dB.

The low meter range is the most useful range, as meaningful readings can be made at relatively low power. Keep in mind that Ic=0.1A flowing in each conductor in a common mode choke with an R component of Z (the effective RF resistance of the choke) of say 1000Ω means (2*0.1)^2*1000=40W of dissipation in the choke.

Fig 1:

Above is a phasor diagram of resolution of currents I1 and I2 into differential and common mode components.

The calculator does not do a lot of error checking, if you enter nonsense, it will probably produce nonsense.

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© Copyright: Owen Duffy 1995, 2021. All rights reserved. Disclaimer.