NF FRA51615, Инструкция по эксплуатации

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5.9 Error correction
5
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34
FRA 51615
5.9.2 Potential slope elimination
When measuring the impedance of batteries or high-capacity capacitors, etc. the DC voltage of the DUT
will change over time together with the charging/discharging state of the DUT. In that case, the signal being
analyzed will be superimposed on a ramp-like waveform, which, in principle, will result in errors with
ordinary discrete Fourier transform (DFT) processing.
Assuming that the signal being measured is composed of a ramp wave and a sinusoidal wave, the electrical
potential slope elimination function can detect the magnitude and phase of the ramp waveform (potential
fluctuation waveform) and the sinusoidal waveform individually. For the analysis, only the obtained
amplitude and phase of the sinusoidal waveform are used; the results for the ramp waveform component
are discarded.
Figure 5-18 Operation of the potential slope elimination function
When the potential slope elimination function is off, errors caused by potential fluctuation that occurs over
one cycle of the sine wave component such as listed in Table 5-1 can occur (theoretical worst-case).
Table 5-1 Error due to potential slope (theoretical values)
Potential
fluctuation in
one cycle
Amplitude
error Phase error
0% 0% 0 deg
1% ±1% ±0.5 deg
10% ±7% ±4 deg
100% ±70% ±40 deg
When the potential slope elimination function is on, errors such as listed in the above table theoretically go
to zero. Actually, however, error due to noise, deviation from the ramp waveform (nonlinear potential
fluctuations) and other such effects remains. Nevertheless, the effects of potential fluctuation are greatly
reduced compared with when the function is turned off. Depending on the conditions, reduction on the
order of several orders of magnitude may be obtained.
t
V
Only the sinusoidal
waveform is
analyzed
Sine wave (amplitude and phase)
Ramp wave (amplitude)