Test Techniques & Applications; Test Sequence; Lead Resistance; Interference And Grounding The Sample - Megger DLRO 600 User Manual

TEST TECHNIQUES & APPLICATIONS
It is important that the potential probes are positioned on the test sample
inside the current probes.

Test Sequence

Pressing the TEST button or selecting AUTOMATIC mode starts the test
sequence.
Continuity of the P1-P2 loop is checked by passing an ac current
(approximately 100 mA @10 KHz) through the test leads and measuring
the ac voltage. Continuity of the C1-C2 loop is not checked until the test
is started; the criteria for continuity is that a current of at least 2 A must be
flowing. If this current cannot be established the instrument will display
"CURRENT LOOP FAIL".

Lead Resistance

The use of a four terminal measuring technique means that the resistance
of the leads is not included in the measurement.
Furthermore, since the potential leads do not carry any current the
type of wire used is not important from the measurement point of view.
However, these leads should be adequately insulated and sufficiently
strong mechanically to support their own weight if long leads are being
used.
The size of the current leads will limit the maximum resistance which may
be measured at full current or may limit the maximum current output to
a level somewhat less than 600 A. DLRO600 can generate 600 Amps into a
total current loop resistance of 7 milliohms if the supply voltage is greater
than 208 V r.m.s.
The 50 mm leads supplied as standard with DLRO600 have a resistance of
2
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2 milliohms each at 20 C and so DLRO600 will be able to measure up to 3
milliohms in the item under test with leads at 20
600 A the leads will warm up and their ability to pass current will decrease
as their resistance increases.
Longer current leads are available if required.

Interference And Grounding The Sample

Ideally the test specimen should be grounded during the test. If it is not
grounded, noise pickup (50/60 Hz etc.) can affect accuracy and increase
measurement errors by up to 1% typically.
Excessive noise will cause the "EXTERNAL VOLTAGE" warning to be
shown.
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C. As you pass
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