Multi-channel safety test
Please first determine whether the corresponding safety unit allows the tested product to use AC voltage or DC voltage, and it should be tested as required. Some products can be tested with AC voltage or DC voltage. Then the manufacturer can decide to use AC voltage test or DC voltage test according to the characteristics of the product. The user must understand the advantages and disadvantages of these two test voltages.
Characteristics of AC Withstand Voltage (ACW) Test
Most products that are tested for withstand voltage will have a certain amount of stray capacitance. When tested with AC, a continuous capacitive current will flow through the stray capacitance.
1. Advantages of AC withstand voltage (ACW) test
◆ Generally speaking, AC test is easier to be accepted by safety regulations than DC test. This is because most of the products use alternating current, and the alternating current test can test the positive and negative polarity of the product at the same time, which is completely consistent with the environment in which the product is used, and is in line with the actual conditions of use.
◆ Unless the product is particularly sensitive to impulse voltage, or the standard requires a slow boost, the AC test can be used to directly apply the full voltage at the beginning.
◆ Generally, there is no need to wait for the discharge after the AC test.
2. Disadvantages of communication testing
◆ If the stray capacitance of the DUT is large or the DUT is a capacitive load, the current generated in the AC test will be much larger than the actual leakage current, so the actual leakage current of the DUT cannot be known.
◆ Another shortcoming is that because the test instrument needs to supply the current required by the stray capacitance, the current that the instrument needs to supply is larger than the current when the DC test is adopted. Sometimes a very powerful instrument is needed to test normally.
Features of DC Withstand Voltage (DCW) Test
During the DC withstand voltage test, the stray capacitance of the object under test will be fully charged, and the capacitive current will eventually drop to zero.
1. Advantages of DC withstand voltage (DCW) test
◆ Once the stray capacitance of the DUT is fully charged, only the actual leakage current of the DUT will remain. Therefore, the DC withstand voltage test can clearly show the actual leakage current of the DUT.
◆ Since it only needs to provide the charging current of the stray capacitance in a short time, and the current required at other times is small, the power of the instrument is much lower than that of the AC withstand voltage test instrument.
2. Disadvantages of DC Withstand Voltage (DCW) test
◆ Unless there is no capacitance on the object under test, the test voltage must rise slowly from “zero” to avoid excessive charging current. The larger the capacitance, the longer the ramp-up time is required, and the voltage that can be increased at a time is also The lower. Excessive charging current will definitely cause misjudgment by the tester and make the test result incorrect.
◆ Since the object under test will be charged during the DC withstand voltage test, after the test, the object under test must be discharged before the next step can be done.
◆ Unlike the AC withstand voltage test, the DC withstand voltage test can only do a single polarity test. If the product is to be used under AC voltage, this shortcoming must be fully considered. This is the reason why most safety organizations recommend the use of AC withstand voltage test.
◆ In the AC withstand voltage test, the peak value of the voltage is 1.4 times the indicated value of the voltage, so most safety units require that if the DC withstand voltage test is used, the test voltage must be increased to the same value.
