HIGH VOLTAGE SURGE: TESTING
In the previous chapter IVa, the nature of the surge voltage waveform as described in the standard IEC/EN 61000-4-5 was illustrated.
The coupling of surge waveforms into a system under test has many variations and a full description might not be possible here as I plan to keep it simple at this stage. I plan to describe specific cases some point of time later where I will include a much more detailed description.
There are general concepts that will be discussed here. In practice all testing is done based on a specific test standard and the standards give detailed descriptions as I am referring to IEC/EN 61000-4-5 standard.
Surges can be applied to both power and data lines. The considerations are similar. The test setup must be able to deliver the stress to the system under test without interfering with system operation before and after the application of the stress. The test setup must also prevent damage or upset to electronics needed to exercise the system under test. This is done with a combination of a coupling network to apply the stress to the system under test and decoupling network to prevent damage or upset to auxiliary equipment. This "Coupling & Decoupling Network" is a commonly known by the short form "CDN". An example is shown in Figure 1 for stressing a set of data lines. The network in Figure 1 allows the stressing of any of the data lines with respect to any of the other data lines or ground. The parallel combination of the capacitor and the surge arrestor feeds the stress into the system. In most cases the arrestor is not included and the surge is coupled into the system capacitively. High speed data lines may not be able to tolerate the micro Farad sized capacitors needed for coupling. An arrestor, such as a gas tube, provides a low capacitive alternative.
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| Figure 1: Typical Surge Voltage Set-up on IO ports |
Test setups for stress to power supply lines are similar. The values of the coupling capacitor may be larger and it is unlikely that the capacitance will be too large so that the use of arrestors for coupling is not needed. Resistors would not usually be used in the decoupling network and capacitive filters may be added between lines on the opposite side of the decoupling network from the unit under test.
The test set-up described above is necessary to understand how surge voltage disturbances are applied to system/equipment under test and might make it easier to understand how to protect the equipment against such disturbances. In the next post we will see some examples of design practices for surge protection.
The test set-up described above is necessary to understand how surge voltage disturbances are applied to system/equipment under test and might make it easier to understand how to protect the equipment against such disturbances. In the next post we will see some examples of design practices for surge protection.
