Operation Manual
MI 3121H Smartec 2,5 kV Insulation / Continuity Insulation resistance
25
I
L
I
L
I
L
Ut Ut
I
A
I
A
I
M
I
M
A
A
+OUT +OUT
-OUT
-OUT GUA RD
Figure 5.10: Connection of GUARD terminal to measured object
where:
Ut ........Test voltage
IL .........Leakage current (resulted by surface dirt and moisture)
IM ........ Material current (resulted by material conditions)
IA......... A-meter current
Result without using GUARD terminal: RINS = Ut / IA = Ut / (IM + IL) …incorrect result.
Result using GUARD terminal: RINS = Ut / IA = Ut / IM ……correct result.
It is recommended to use the GUARD connection when high insulation resistance
(>10G Ω) is measured. You need optional 2.5 kV 3-wire test lead (Figure 5.3).
The guard terminal is internal impedance (660 kΩ) protected.