33
4.6. fILtEr kEy
When the instrument detects that the measurement is disturbed by an AC voltage hat is too large, it switches an analogue filter
onto the terminals and so indicates by displaying the DH symbol (Disturbation High).
FILTER
Press the FILTER key. Each press modifies or removes the filter:
DF 10: time constant 10 seconds,
DF 20: time constant 20 seconds,
DF 30: time constant 40 seconds,
no filter.
The filter is calculated as follows:
R
N
= R
N-1
+ (R - R
N-1
)/N
If N is set to 20, the time constant of this filter will be approximately 20 seconds.
10 100 1
10
10
10
100
1
100 1
k
Ω
M
Ω
G
Ω
T
Ω
303.3 M
Ω
3.244 µA
Elapsed Time 00:00:48
984 V
ALARM
DH
I-LIM
Complementing this, the FILTER key can be used to activate and deactivate a digital filter for the insulation measurements. This
filter affects only the display (which is smoothed), not the measurements. The recorded data therefore remain raw (no filter).
This function is useful in case of high instability of the insulation values displayed, but it is also possible to estimate the measurement
on the bargraph.
DF 20s
10 100 1
10
10
10
100
1
100 1
k
Ω
M
Ω
G
Ω
T
Ω
303.3 M
Ω
3.244 µA
Elapsed Time 00:00:48
984 V
ALARM
DH
I-LIM
Selecting digital filtering (DF) is recommended for measurements of fluctuating high insulation resistance values. Such fluctuations
may be due to hand effects, 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 key is active before and during the measurement.
