iv
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Safety Notes
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Accuracy
We define measurement tolerances in terms of rdg.
(reading) values, with the following meanings:
rdg. (displayed or indicated value)
This signifies the value actually being measured,
i.e., the value that is currently indicated or displayed
by the measuring instrument.
Measurement categories
To ensure safe operation of measurement
instruments, IEC 61010 establishes safety standards
for various electrical environments, categorized as
CAT II to CAT IV, and called measurement
categories. These are defined as follows.
CAT II: Primary electrical circuits in equipment
connected to an AC electrical outlet by a
power cord (portable tools, household
appliances, etc.)
CAT II covers directly measuring electrical
outlet receptacles.
CAT III: Primary electrical circuits of heavy
equipment (fixed installations) connected
directly to the distribution panel, and
feeders from the distribution panel to
outlets.
CAT IV: The circuit from the service drop to the
service entrance, and to the power meter
and primary overcurrent protection device
(distribution panel).
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