Appendix 6 Terminology
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Maximum effective peak
voltage
Maximum effective peak
current
The maximum effective peak voltage (current) refers to the maximum peak value (crest
value) for the input waveform that can be processed as a valid measured value by the
instrument. This value indicates the internal circuitry’s dynamic range. For some measuring
instruments, this value may also be called the crest factor. (Since the PW3335’s maximum
effective peak voltage and maximum effective peak current are ±600% of each range, the
crest factor is 6. However, the value is ±1,500 V peak for the 300 V, 600 V, and 1,000 V
ranges and ±60 A peak for the 20 A range.)
When using an instrument whose internal circuitry has a narrow dynamic range to measure
a distorted wave with a small RMS value but a large peak value, the distorted wave’s peak
may become saturated (clipped), preventing accurate measurement.
The following figure illustrates an example in which an input current waveform with a crest
factor of 5.4 (RMS value of 10 mA and peak value of ±54 mA) is measured using the 10 mA
range.
Since the dynamic range for the 10 mA range, with which an RMS value of 10 mA can be
measured with the greatest accuracy, is ±30 mA, portions of the waveform exceeding this
level will be clipped, preventing accurate measurement. While exceeding the internal cir-
cuitry’s dynamic range can be avoided by increasing the measurement range, this has the
effect of lowering the measurement resolution and increasing measurement error.
Since the PW3335 has a dynamic range of ±60 mA for the 10 mA range, the 10 mA range,
which is the optimal range, can be used.
In addition, the peak-over lamps (PEAK OVER U and PEAK OVER I) will light up if input
exceeding this dynamic range is received in order to notify the user that the data is invalid.
MCR
A value used to determine the maximum permitted uncertainty in power measurement as
defined by “IEC 62301:2011 Household electrical appliances – Measurement of standby
power.” Under the standard, MCR is calculated using the following formula:
Maximum current ratio (MCR) = Crest factor (CF) / Power factor (PF)
Terminology Description
Example using an instrument with a narrow dynamic range (crest factor of 3)
PW3335 (crest factor of 6)
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