MI 3201 TeraOhm 5 kV Plus Measurements
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5.3 Filter options
Filters are built in to reduce the influence of noise on measurement results. This option
enables more stable results especially when dealing with high Insulation Resistances
(Insulation Resistance, Diagnostic Test, Step Voltage). In these functions, the status of
the filter option is shown in the top right corner of the LCD screen. The table below
contains a definition of the individual filter options:
Fil0 Low pass filter with cut off frequency of 0.5 Hz in signal line.
Fil1 Additional low pass filter with cut off frequency of 0.05 Hz in the signal
line.
Fil2 Fil1 with increased integrating time (4 s).
Fil3 Fil2 with additional cyclic averaging of 5 results.
Table 2. Filter options
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.
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