Megger DET2/2 Guia Del Usuario página 33

VDE 0413 part 7 specification stipulates that these
instructions should contain a table or diagram showing
the maximum value which the instrument must indicate
in certain conditions. An earth test being performed on
any electrode system would normally be carried out to
a particular specification. Therefore, even at the iworst
accuracy of the instrument, the reading is never above
the limiting value required
specification in question.
The table overleaf shows the maximum reading which
shall be indicated by the instrument (at its maximum
error) to ensure that the maximum value of the earth
resistance given in the relevant earth electrode test
specification is met.
Note: The decimal point position in the Maximum
Resistance value column is correct for resistance
readings < 2 Ω. For the 2 Ω to 20 Ω column and the >
20 Ω column, the decimal point should be moved
accordingly. For maximum readings in excess of 200 Ω
use the right hand column and adjust the decimal point
accordingly.
The table gives the maximum reading that would be
allowed for a known maximum resistance value,
assuming the instrument is used as specified.
If a maximum resistance is known, this value is found
from the left hand column. The maximum reading to be
by the particular
given by the instrument is found by reading across to
the appropriate of the three right hand columns,
depending upon the range of the value to be measured.
For example If 10 Ω is the value of the maximum
resistance, since this is less than 20 Ω, the centre
column of the three right hand columns is used. This
shows that a reading of less than 9,49 Ω will ensure
that, allowing for instrument tolerances, the measured
resistance will be less than 10 Ω.
A maximum value may be given to a measurement by
using the table in reverse. For example, a reading of
1,545 Ω would give a maximum limit to the resistance
value of between 1,600 Ω and 1,650 Ω. Interpolation
can be used to increase the accuracy if required.
Note: This table can only be used for readings from a
DET2/2.
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