The test probes should always be in contact with the DUT
before the start key t is activated.
If the DUT is charged with voltage, measurement is disabled if
the test probes are first placed into contact with the DUT.
If you press the Start t key first, and then make contact with
the test probes, the external fuse is blown. Which of the two
fuses has blown is indicated in the popup window with the
error message.
In the event of single-pole measurements, the result is included in
the database as RLO.
Automatic Polarity Reversal
After the measuring sequence has been started, the instrument
performs measurement with automatic polarity reversal, first with
current flow in one direction, and then in the other. In the event of
permanent measurements (press and hold the START key) polar-
ity is reversed every other second.
If the difference between RLO+ and RLO– is greater than 10%
during automatic polarity reversal, the RLO+ and RLO– values are
shown instead of RLO. The higher value for RLO+ and RLO–,
respectively, is shown at the top and is included in the database
as RLO value.
Evaluating Measurement Results
Differing results for measurements in both directions indicate
voltage at the DUT (e.g. thermovoltages or unit voltages).
Measurement results can be distorted by parallel connected
impedances at load current circuits and by equalizing current,
especially in systems which make use of “overcurrent protection
devices” (previously neutralization) without an isolated protective
conductor. Resistances which change during measurement (e.g.
inductance), or a defective contact, can also cause distorted
measurements (double display).
In order to assure unambiguous measurement results, causes of
error must be located and eliminated.
In order to find the cause of the measuring error, measure
resistance in both directions of current flow.
The instrument’s batteries are exposed to excessive stress during
insulation resistance measurement. For measurement with
current flow in one direction, only press and hold the START t key
as long as necessary for the measurement.
Measuring Low-Value Resistance
Measurement cable and 2-pole measuring adapter
resistance is compensated for automatically thanks to the
four conductor method and does not effect
measurement results. However, if an extension cable is
used its resistance must be measured and deducted
from the measurement results.
Resistances which do not demonstrate a stable value
until after a “settling-in period” should not be measured
with automatic polarity reversal, but rather successively
with positive and negative polarity.
Examples of resistances whose values may change
during measurement include:
– Incandescent lamp resistance, whose values change
due to warming caused by test current
– Resistances with a great conductive component
– Contact resistance
Evaluation of Measurement Values
See Table 4 on page 57.
Calculation of Cable Lengths for Common Copper Conductors
If the HELP key is activated after performance of resistance mea-
surement, the cable lengths corresponding to common conduc-
tor cross sections are displayed.
If results vary for the two different current flow directions, cable
length is not displayed. In this case, capacitive or inductive com-
ponents are apparently present which would distort the calcula-
tion.
This table only applies to cables made with commercially available
copper conductors and cannot be used for other materials (e.g.
aluminum)!
Polarity Selection Display Condition
+ pole against PE RLO+ none
– Pole against PE RLO– none
pole against PE
RLO if RLO 10 %
RLO+
RLO–
if RLO > 10 %
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