8
Safety Information
We define measurement tolerances in terms of rdg. (reading)
and dgt. (digit) values, with the following meanings:
rdg. (reading or displayed value)
The value currently being measured and indicated on the
measuring instrument.
rdg. (reading or displayed value)
The smallest displayable unit on a digital measuring instrument,
i.e., the input value that causes the digital display to show a “1”
as the least-significant digit.
This instrument complies with CAT III safety requirements.
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.
Using a measurement
instrument in an
environment designated
with a higher-numbered
category than that for
which the instrument is
rated could result in a
severe accident, and must
be carefully avoided.
Use of a measurement
instrument that is not
CAT-rated in CAT II to CAT IV measurement applications could result in a
severe accident, and must be carefully avoided.
Accuracy
Measurement categories
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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