True RMS current for neutral

[EvonneYin]

Hi All,

I hope anyone of you could help me on this one. Does ION7300 have true RMS current for neutral reading?

I found an information which shows I4-residual current calculation as current flow in the neutral.

Is it calculated and not true RMS reading?

Please advise.

Regards,

Evonne

[Anonymous user]

Hi Evonne,

Not sure whether you have found the answer to your question by other means.

Anyway, the ION73xx series does not have I4 current input hence it is not true RMS measurement. The next model up ION7550 & ION7650 have I4 and I5 input for CTs.

Regards

Ed

[JamesAZZO]

As do the new PM556x meters...

[Anonymous user]

"true RMS" is generally accepted to indicate a measurement for any waveshape that is proportional to heat dissipated by a resistive load attached to this signal (as opposed to assuming the signal is sinusoidal).

The 7300 series does not have a physical I4 terminal so it (obviously) is a derived quantity. Derived does not mean that it is or is not true rms, but in the case of the 73xx I4 is a vector summation of fundamental phase currents (so not true RMS).

The PM8000 and 86xx do compute true RMS of a derived residual current. The 75/7650 series has additional terminals to make real measurements.

[engineer_langfo]

One side note: the ION8650 series does not calculate I4 (residual current).   This value (for whatever reason) is missing in the ION8650.

The inputs of the ION7550/7650 will return a 0 if there is no CT in the I4. 

Besrat gave me this great equation to calculate residual current which is only valid for ION OS meters with Power Harmonics Module.  Apparently it is in a KB article, and referenced elsewhere, but I cannot seem to find...

___________________________________________________________________________

- Create a Power Harmonics Module

- In setup registers set the harmonic number to 1 (the fundamental)

- Create arithmetic that acquires values for I1, I2 and I3 magnitude and phase from the PHM above.

- using the arithmetic, decompose these signals into rectangular components with:

Inx = |In|*cos(angleIn)

Iny = |In|*sin(angleIn)

for each phase.

- now seperately add the x and y components of each phase giving a total x and y.

I4x = I1x + I2x + I3x

I4y = I1y + I2y + I3y

- using an arithmetic, find the magnitude of the fundamental I4 with:

|I4| = sqrt((I4x)^2 + (I4y)^2)