Equivalent circuit
The block diagram and equivalent circuit show the measuring principle of
CLAMP EARTH TESTER.
When the auto sweep signal (4kHz to 200kHz, 160mV p-p) is injected into the
circuit, the resonance phenomenon is caused at the certain frequency by
inductance (L) and electrostatic capacity (C
0
) or DC resistance (r) and
electrostatic capacity (C
1
) in the circuit, and the current flow (i) is caused. When
the resonance phenomenon is caused, the current flow (i) become maximum.
The injected current (i) into the circuit is proportional to the earth resistance (R
B
)
and this current (i) is measured by the measuring CT and used for the
computation of the earth resistance value (R
B
) with other calculation factors.
The resonance phenomenon is caused almost at 4kHz to 200kHz frequency in
our field test.
Note
: If the resonance phenomenon is not caused in the circuit, the current
flow (i
2
) is caused and the measured resistance value become R
B
+ R
D
+Z
c
. This resistance value will be higher than the actual value
abnormally, or over range indication “OVER” will be displayed.
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