mpec SA380-IT, Руководство пользователя

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The graph below shows a typical measurement current trace of the SA380-IT:
By applying a test pulse of alternating polarity, the test pulse current becomes a "differential" current reading, whilst the current due to the
supply circuit becomes a "common" current reading.
2.6) Core-to-Core Resistance Effects
2.7) Earth Integrity Measurement
Every 30 seconds the integrity of the SA380-IT functional earth connection is validated by measuring the resistance between the primary
(Functional Earth) and secondary (Loop Earth) earth connections.
This gives confidence that the earth connection is "good" and therefore reliable Resistance to Earth measurement of monitored circuits can
be conducted.
In the case where two wholly independent earth points have been provided (1), it verifies that the functional earth connection is
intact, and that connection to the physical mass of the earth is also of sufficiently low resistance.
In the case where two independent wires have been run to a common earth point, (2) it verifies that the wiring of the functional earth
connection is intact.
Single & Double Earth Points:
By taking the difference of the measured current for the positive and negative measurement pulse signals, the "common" current is
eliminated allowing the calculation of equivalent resistance to earth (R ).
L
By taking the sum of the measured current for the positive and negative measurement pulse signals, the "differential" current is
eliminated. In the case of DC circuits, this allows the direct calculation of the resistance of each circuit leg R and R .
B N
Please note:
When R > 20 x R . Then the accuracy of
B N
R will
B
/-5%
When R > 20 x R . Then the accuracy of
N B
R will
N
/-5%
This is due to it becoming increasingly difficult to measure a large resistance to earth in one leg of a circuit, when the resistance to
earth in the other leg of the circuit becomes relatively small.