Megohmmeter
Model 24508
Page 41
Technical data
General informa
-
tion
Pr
eparations for
use
Contr
ols and con
-
nections
Manual operation
of the unit
Contr
olling the
unit r
emotely
Maintenance and customer service
APPENDIX
General information on the meg-
ohmmeter
Basically a megohmmeter consists of a precision voltage source connected in series
with a measuring circuit that enables measurement of the current flowing through an
object under test. The value of this current can be very small (less than a few nA); this
means that errors in the reading can easily occur as a result of various forms of interfer-
ence or even unwanted leakage currents flowing in parts other than the object under
test (cable insulation, holders etc.). Using screened cables and a reference potential - a
potential very close in value to the test voltage - it is possible to reduce these interfer-
ence effects and to perform cable screening tests when required.
The most common test situation:
The test voltage connected to ground is applied to the „Rx“ point of the object under
test. The „X“ input (protected by the guard potential) of the megohmmeter is connected
to the „hot“ point of „Rx“.
Cable-screening measurement case
The leakage currents are diverted away via the guard potential, and have no effect on
the current flowing through the object under text „Rx“. This principle lets you perform
numerous of applications (see examples).
