Filter Button - AEMC 6550 User Manual

2.4.6 FILTER Button

The FILTER button can be used to activate and deactivate a digital filter for the insulation measurements. This
filter affects only the displayed results (which are smoothed), not the measured values. The recorded data
therefore remains raw (no filter).
This function is useful in the case of high instability of the insulation values displayed, but it is also possible to
estimate the measurement on the bargraph.
Once the measurement starts, if interference is present, press the FILTER button. Start by applying the DF10s
filter. If that is not enough, go to the DF20s filter, then to the DF40s filter. The larger the time constant, the
smoother (and slower) the measurement.
Successive presses on the FILTER button will modify or remove the filter:
■
DF 10: time constant 10 seconds
■
DF 20: time constant 20 seconds
■
DF 40: time constant 40 seconds
■
no filter
The filter is calculated as follows:
RN = RN-1 + (R - R )/N
N-1
If N is set to 20, the time constant of this filter will be approximately 20 seconds.
Selecting digital filtering (DF) is recommended for measurements of fluctuating high insulation resistance values.
Such fluctuations may be due to hand movement, when touching the cables, fluctuating capacitances in the
device tested, insulation that varies because of conducting dust, an ionizing and polarizing effect of this dust,
etc., or again to the presence of an AC voltage superposed on the measurement.
The FILTER button is active before and during the measurement (but is not available in graph mode).
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303.3 MΩ
984 V
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kΩ
MΩ
1 1
10
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FIXED VOLTAGE
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Date 2011.05.23
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