MI 3200 TeraOhm 10 kV
Measurements
19
THE PURPOSE OF FILTERING
In simple terms the filters smooth the measured currents by means of averaging and
bandwidth reduction. There are various sources of disturbance:
-
AC currents at the mains frequency and its harmonics, switching transients etc,
cause the results to become unstable. These currents are mostly cross talk through
insulation capacitances close to live systems,
-
Other currents induced or coupled in the electromagnetic environment of the
insulation under test.
-
Ripple current from internal high voltage regulator,
-
Charging effects of high capacitive loads and / or long cables.
Voltage changes are relatively narrow on high resistance insulation, so the most
important point is to filter the measured current.
Note:
Any of the selected filter options increases the settling time with Fil1 to 60 s, Fil2 to 70 s,
and Fil3 to 120 s.
-
It is necessary to pay close attention to the selection of time intervals when using the
filters.
-
The recommended minimum measuring times when using filters are the settling
times of the selected filter option.
Example:
A noise current of 1 mA / 50 Hz adds approximately
15 % distribution to the measured
result when measuring 1 G
.
By selecting FIL1 option the distribution will reduce to less than
2 %.
In general using FIL2 and FIL3 will further improve the noise reduction.
5.4. Voltage measurement
Selecting this function displays the following states (initial state and state with results
after completion of the measurement, see the
Fig. 9
).
Fig. 9. Voltage function display states
Measurement procedure:
-
Connect the test leads to the instrument and to the measured source.
