App-21
IM WT310E-01EN
Appendix
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App
Index
Appendix 5 Measurement Accuracy and
Measurement Error
Instruments such as power meters have specifications for measurement accuracy or measurement
errors. For example, on this instrument, the voltage and current accuracy in the range of 45 Hz to 66
Hz is ±(0.1% of r 0.05 % of range).
Reading Error and Range Error
Reading error: of reading
The error indicated by “of reading” is called reading error. The error is calculated on the basis of the
measured reading. It is an error that is included at a given ratio of the measured values. The larger
the measured value, larger the reading error that is included. The smaller the measured value,
smaller the reading error that is included.
Range error: of range
The error indicated by “of range” is called range error. The error is calculated on the basis of the
measurement range that is used in measurement. It is an error that is included at a given magnitude
in the measured values. The range error that is included is of the same magnitude regardless of
whether the measured value is large or small.
Input signal
Measured
value
–error
+error
Reading error
Input signal
–error
+error
Range error
Input signal
–error
+error
Reading error + range error
Measured
value
Measured
value
0
0
0
To see how much error is included in the measured values, let us look at several computation
examples for a 60 Hz sine wave input signal.
Voltage and Current Measurement Error
Example 1: Measuring 1 Arms Using the 1 A Measurement Range
When the measured value is 1.0000 [A], the reading error and range error are as follows:
• Reading error: 1.0000 [A]×0.1% = 0.001 [A]
• Range error: 1 [A]×0.05% = 0.0005 [A]
The error included in 1.0000 [A] is the sum of the reading and range errors, which is ±0.0015 [A]. This
corresponds to 0.15% of the displayed value.
Note
Application of an input signal whose value is the same as the name of the measurement range is referred to
as rated range input. And, such input signals are called rated range signals.
