GOSSEN-METRAWATT
19
Different results obtained when measuring in both directions
of the current point to external voltages on the device under
test (e.g. thermovoltages or element voltages). Particularly
in systems where the protective means „overcurrent protec-
tive device“ (formerly null method) is used without a sepa-
rate protective conductor, the measured results can be
falsified by impedances of operating circuits connected in
parallel and by equalizing currents. To obtain unambiguous
measured results, it is required to eliminate the cause of the
fault.
í
When you briefly press the pushbutton „AUTO /
⊗
“ (2),
the tester switches back to resistance measurement with
automatic polarity reversal.
Notes on measuring low-ohmic resistances:
• A low-ohmic measurement is made in four-wire connec-
tion, whereby the leads are run up to the probes. The
resistance of the fixed test leads does not enter into the
measured result for that reason. If you use an extension
cord, you must measure its resistance and deduct this
value from the measured value obtained.
• To also enable the measurement of larger resistances as
required by DIN VDE 0413 Part 4, the measuring span of
the digital display is larger by one decade (up to 30
Ω
)
than that of the analog indicator (up to 3
Ω
).
• On the low-ohmic measuring range, the tester is pro-
tected against overload by a superquick-acting fuse
FA 0.315 A /1000 V. With a blown fuse, only the voltage
measuring range functions (R
i
= 5 M
Ω
). When you press
the measurement pushbutton in the „
Ω
“ function, the
word „FUSE“ is shown in place of the digital display.
• Resistances that reach a stable value only after a „tran-
sient response“ should only be measured after manual
selection of the direction of the current. A measurement
with automatic polarity reversal can lead to different and
to higher measured values and thus to an ambiguous
display.
Resistances whose values change at the beginning of the
measurement, are, for instance:
• Resistances having a high inductive content
• Resistances of light bulbs whose values change due to
heating caused by the measuring current
• Poor contact resistance at the contact points.
8.3
Finding the max. display values
regarding the maximum service error:
Limit
Ω
Max. display values
Ω
0.2
0.16
0.3
0.25
0.4
0.35
0.5
0.44
0.6
0.53
0.7
0.62
0.8
0.71
0.9
0.80
1.0
0.89
1.5
1.35
2.0
1.80
2.5
2.25
3.0
2.71
3.5
3.16
4.0
3.62