Annex B Safety Knowledge
58
In general, safety regulations will prefer ACW than DCW, for most products use AC
power supply. The ACW can simultaneously test the positive and negative polarity of the
product, consistent with the actual operating environment.
Because the discrete capacity cannot be fully charged during ACW, but there will not be
instant impact current, and it is unnecessary to keep the voltage rising slowly. Apply full
voltage at the start of test, unless such product is sensitive to shock voltage.
Because the discrete capacity cannot be fully charged during ACW, do discharge is
unnecessary after the test, which is another advantage.
2 Disadvantages of ACW
For the current required to charge the discrete capacity of DUT, the output current will
be much higher than the current during DCW. This will increase the danger of the operator.
B.4.3 Features of DCW
For DCW, the discrete capacity of the DUT will be filled, the capacitive current caused
by DCW will drop to zero after the capacity is fully charged.
1 Advantages of DCW
After the discrete capacity of the DUT is filled, only the actual leakage current exists,
which can be displayed clearly.
Another advantage is that the charging current of the DUT is only supplied in a short
time, the current required to supply in other time is low, and the current capacity is much
lower than that for ACW.
2 Disadvantages of DCW
Unless there is no capacity exists, the test voltage must raise slowly from Zero to avoid
too large charge current, the higher the capacity, the longer the ramp time, and the lower the
increased voltage. Too large charge current will cause misjudgment by the analyzer, and the
test results are incorrect.
As the DUT may be charge during DCW, be sure to discharge the DUT after the test
before the next step.
Different from ACW, DCW can only apply for single polarity test. If the product works
with AC voltage, this disadvantaged must be considered. So most safety units recommend
adopting ACW.
For ACW, the peak voltage is 1.4 times of the reading of the meter, which is not
displayed by the meter in general, and not achieved during DCW. So most safety units
require that, if DCW is adopted, the test voltage must be increased to equal value.
B.4.4 Difference between arc detection and ACW/DCW
ARC
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