Test Sequence; Test Lead Resistance; Overheating - Megger Ducter DLRO-10 Guia Del Usuario

Test Techniques & Applications

TEST SEQUENCE

Pressing the TEST button starts the test sequence.
Contact resistance is checked by passing 100 µA through the
C1-C2 loop and checking that the voltage is less than 4 V. Then
passing 80 mA through the P1-P2 loop and checking that the
voltage is less than 250 mV. If either value is exceeded the
respective lamp or warning message will be displayed.
When all faults have been rectified the test current is increased
until the voltage on P1-P2 is within the 2 mV to 20 mV range.
This current is then applied in a forward and then reverse
direction to obtain two measurements.
Both measurements are displayed by DLRO 10X along with the
average, while the DLRO 10 displays the average only.
If the combined resistance of the current leads and test sample
is greater than 100 mΩ, testing at 10 A will not be possible.
A 1.9 mΩ resistor will then be tested at the next lowest current
(1 A) and the result will be shown as 1.900 mΩ instead of
1.9000 mΩ.

TEST LEAD RESISTANCE

For testing at 10 A, the combined resistance of the current leads
must not exceed 100 mΩ. This will ensure that the voltage drop
in the leads is less than 1 volt and will enable 10 A testing under
worst case conditions. If you wish to limit test current to no more
than 1 A, on DLRO 10 use current leads with a resistance of
about 1 Ω, or on DLRO 10X select 1A as the maximum test
current on the RANGE submenu.
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OVERHEATING

When performing rapidly repeated tests at 10 A, using current
leads with a combined resistance of 100 mΩ, 10 W of heat will
be dissipated in the leads and 30 W within your instrument. If the
ambient temperature is high this will cause internal overheating
and the message "hot" will appear on the instrument display and
testing will be halted.
After a few minutes to cool down, testing will be allowed to
continue.
If this is a persistent problem, use current leads with a higher
resistance (e.g. 200 mΩ to 300 mΩ). This will reduce the
generation of internal heat.