Condition And Warning Indicators - Megger BM11D Guide De L'utilisateur

Operation
In cable testing, there may be a path of leakage across the
insulation between the bared cable and the external sheathing,
perhaps due to the presence of moisture or dirt. Where it is
required to remove the effect of this leakage, particularly at high
testing voltages, a bare wire may be bound tightly around the
insulation and connected via the third test lead to the guard
terminal 'G'.
Since the leakage resistance is effectively in parallel with the
resistance to be measured, the use of the guard causes the
current flowing through the surface leakage to be diverted from
the measuring circuit. The tester, therefore, gives more nearly
the true insulation resistance.

CONDITION AND WARNING INDICATORS

FS2
A failed guard fuse will not be detected unless the guard
terminal is in use. If the FS2 indicator flashes when the guard
lead is in use it is likely that the guard fuse (FS2) has ruptured.
If the FS2 indicator flashes when the guard lead is not
connected, it indicates failure of one of the batteries or a battery
fuse (which is not accessible externally). The instrument will
operate normally in this condition, although the operating time
between charges will be reduced, no capacitance readings will
be provided and no warning will be given if the guard fuse
blows.
BREAKDOWN
The BM21 has a breakdown detector which terminates the test
if a breakdown of the circuit occurs. The 'BREAKDOWN'
indicator cursor will then flash to identify the cause of the test
termination. Selecting the 'BURN' mode prior to the test
disables the 'BREAKDOWN' indicator.
11
The BM11D does not have a breakdown detector and is
therefore effectively in permanent 'BURN' mode. When using
the BM11D (or BM21 in 'BURN' mode) testing will continue if
a breakdown occurs in the circuit under test. In very dry
conditions, a high frequency arc can be generated. This may
cause a disturbance to, and possibly a complete loss of the
instrument display. In these circumstances it is important to
remember that the circuit may still be energised.
If in any doubt, switch the instrument to 'OFF' and
manually discharge the circuit before touching any
connections.
EXT VOLTS
Display of the 'EXT VOLTS' cursor, indicates that the voltmeter
is reading a voltage which originates from an external source.
The voltmeter will show d.c. voltage of either polarity or a.c.
voltage.
NOISE (BM21only)
If an external interference (normally 50 Hz or 60 Hz hum
current) is excessive (>2 mA at 5 kV), testing will terminate, and
the noise indicator will flash.
(Note: trips at approx. 1,5 mA at <2 kV).
Error Numbers
Internal faults and errors will cause the display to show 'E'
followed by a number. These error numbers can be invoked by
extreme cases of electromagnetic interference or by internal
faults, in which case the number is of little significance. The
only meaningful error numbers are E5 and E11 which indicate
that a negative current has been measured.
Calibration Errors
At switch-on there is a calibration check which automatically