User manual

22 GMC-I Messtechnik GmbH
Start Measurement
Measurement of + pole to
PE
Measurement of – pole to
PE
Final results
Attention!
!
The measurement cannot be started until the test probes
are in contact with the device under test.
If a voltage of U > approx. 3 V is present at the device
under test, a pop-up window appears which warns
against interference voltage.
This error message must be acknowledged and/or
cleared by any desired key. Eliminate the interference
voltage.
If resistance is greater than 10 Ω, OL appears at the dis-
play.
In the case of single-pole measurement, the respective value is
saved to 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.
If the difference between RLO+ and RLO– is greater than 10%
with automatic polarity reversal, RLO+ and RLO– values are dis-
played instead of RLO. The respectively larger value, RLO+ or
RLO–, appears at the top and is saved to the database as the
RLO value.
Resistances which do not demonstrate a stable value until after a
“settling in period” should not be measured with automatic polar-
ity reversal. Measurement with automatic polarity reversal may
lead to varying and/or inflated measurement values, and thus to
an ambiguous reading.
Limit Value Indication
If the measured value is less than or equal to 2 Ω, the limit LED
lights up green. If the measured value is greater than 2 Ω, the LED
lights up red.
Evaluating Measurement Results
Differing results for measurements in both directions indicate volt-
age 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” (previous 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 measuring error, measure resistance
in both current flow directions.
Note
Measuring Low-Value Resistance
If an extension cable is used its resistance must be mea-
sured 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 one after the
other 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 large conductive component
– Contact resistance
Polarity Selection Display Condition
+ pole to PE RLO+ None
– pole to PE RLO– None
± pole to PE
RLO If ΔRLO ≤ 10%
RLO+
RLO–
If ΔRLO > 10%
START