Test Sequence; Test Lead Resistance; Overheating - Megger DLRO-10 Guide De L'utilisateur

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 µA 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.

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
15
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.