Chroma 66203, Руководство пользователя

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Operation
4-9
4.4 Computing Equation for Measurement
Parameters
Following explains the computing equation for the measurement parameters of true rms
value, mean value, maximum value, crest factor, integration and frequency.
The 66203/66204 Digital Power Meter will sample the input voltage and current waveform
simultaneously. The calculation of rms values includes both AC and DC portions while the
AC waveform could be distorted, thus the rms value is true rms value. The calculation of
delivered power and received power also includes the AC and DC portions of voltage and
current waveform, thus the value of active power (
W
) is true power value and the
positive/negative sign indicates the power direction. The power factor definition is the
proportion of average power and apparent power which is from the viewpoint of providing the
average energy required. In fact, the power factor is between 0~1 without positive/negative
sign; however, it often has positive/negative sign on the power meter to indicate phase
relationship of current leads or lags voltage. The positive sign indicates a leading current
and the negative sign indicates a lagging current. The power factor calculation of the
66203/66204 Digital Power Meter contains the portion of fundamental wave and all harmonic
distortion. It also takes the displacement power factor caused by the phase difference
between voltage and current fundament wave as well as the calculation of distorted power
factor caused by harmonic portion into consideration. Thus, it is the true power factor.
Besides the measurement of rms value, the 66203/66204 Digital Power Meter also has DC
measurement. If the input voltage and current waveform has AC and DC portion, the period
average of AC waveform is able to get the average value of voltage and current while the
power is the product of average voltage and average current.
The measurement of maximum voltage and current is to get the maximum of positive and
negative half waves from the waveform period. The crest factor (CFi) is calculated from the
peak amplitude of the current waveform divided by the rms value of the current waveform.
The crest factor of sine wave is 1.414. For distorted or rectified waveform, the CFi is usually
larger than 1.414.
The 66203/66204 Digital Power Meter follows the definition of IEC to total harmonic
calculation to compute the ratio of the sum of the squares of the rms value at all higher
harmonic frequency waveforms to the square of the rms at the fundamental waveform. The
power meter gets the voltage and current sampling data through the analog/digital converter,
and sends the sampling data back to DSP for Fourier conversion to get the valid value of
fundamental wave and harmonic of each level for THD. For the detail of THD measurement,
please see section 4.6.2.
The integration is to calculate the average energy and power for a period of time. The time
can be defined by the user. The average energy measurement is often applied to evaluate
and monitor the usage of house appliance in a long period of time. The average power
measurement is applied to the UUT running under a period of time or certain mode to
measure the input or output average power repeatedly for efficiency evaluation. The function
of average energy and average power measurements can work in parallel as both of them
can be operated separately.