Circuit Block Diagram - Megger MIT520/2 User Manual

terminal, or at least 10 kΩ for the negative terminal.
Conversely, if the positive terminal is grounded, then the negative terminal
will be at a voltage equal to the test voltage relative to ground, which will
result in an increase in leakage current, and worsening of measurement
accuracy.
+ Test V
+
When making measurements above 100 GΩ therefore, the user should
ground the Guard Lead where possible, otherwise parallel leakage paths
may occur.
Alternatively, screened leads are available as an optional accessory from
Megger. The lead to the negative terminal is fully screened. The screen is
plugged into the Guard terminal, diverting any stray leakage currents. This
considerably improves measurements made with a floating output, where
the leads might touch each other or anything other than the test piece.
18
0V
-
Guard
Ground

Circuit block diagram

R1
100 MΩ
High C1
-
voltage
+
source
Ref
Current
Limit
Voltage
control
Current
For 5 kV instruments C1 = 47 nF, R1 = 50 kΩ, R2 = 40 kΩ
For 10 kV instruments C1 = 15 nF, R1 = 156 kΩ, R2 = 110 kΩ
R2
+
Volts
Discharge
resistance
G
Fuse
-
Cable
under
test