33
Making Leakage Tests
When testing for leakage on large capacitors, the first
reading returned by the LC103 may be outside the
normal leakage limits because the capacitor is charging.
In the case of electrolytics, several readings may be
needed before the capacitor drops to a “GOOD” level,
since an electrolytic usually takes some time to charge.
This means that the computer software should ignore the
first few readings in order to accept a meaningful
reading.
There are several ways to handle this in the software. For
example, the program could place the LC103 into the
leakage function (with the “LKI” listener code) and then
set a software timer to insert the correct delay (based on
the normal charging time of the capacitor) before
reading the leakage value. During this time, the
computer could work with other instruments on the bus
to keep the delay from slowing down other steps in the
automated system. Rather than a fixed time delay, the
software can be written to ignore a certain number of
readings before recording the one which is to be checked
for value.
In either case, the computer can base its decision on
whether the capacitor is good or bad by using the
GOOD/BAD Indicator in the returned data. For the
automatic GOOD/BAD test to function the capacitor's
value, voltage, and type must be sent to the LC103 prior
to the test. This allows the LC103 microprocessor to
compare the leakage readings to the internal formulas
and tables.
Making ESR Tests
The capacitor test for Equivalent Series Resistance may
cause unexpected program errors if your software does
not handle the returned data correctly. Remember that
ESR tests are only valid on electrolytic capacitors with
values larger than 0.01 microfarad. Also remember that
some capacitors may have such high levels of ESR that
the value is above the measuring range of the test.
Therefore, make certain that your software tests for the
following conditions.
1.
An “ERR 1” occurs if any component type other than
ALM, DBL, HIR, or TAN has been sent to the
LC103 in its listener mode.
2.
An “ERR 3” occurs if the capacitor under test
measures less than 0.01 microfarad.
3.
An “ERR 7” occurs if the amount of ESR is above
2000 ohms.
4.
The leads must be zeroed (either manually or by
using the “LDS” listener function) before making
ESR tests, or the added lead resistance may cause
erroneous results.