All the products designed in the market might have to be operated in not so condusive environments. For this it has they have to be tested before releasing to the market. There are several compliance tests in the market to certify a product. Electrical Fast Transient (EFT) Immunity test is one of the common compliance test in embedded systems. It is important the system is immune to EFT. IEC 61000-4-4 defines the standards for the EFT. This standards helps designers to understand the test procedure to be followed to qualify a product. One has to understand that passing EFT test is more of a internal design aspect of the system rather than the whole system. Many designs which didn't have a proper protection fail in the compliance tests and have to go back to the lab taking out lot of time and design efforts, design modifications leading to long product lead times. These all lead to the companies getting into losses in that particular product model.
In a real time scenario, when there are loads like motors, other inductive loads connected to the circuit, there can be a chance that a short time-period transient with high-frequency may be generated. Electrical Fast Transients (EFT) are caused by transient currents during a make or break of contact. This is also called arcing. These transients can damage the system. So, an appropriate protection mechanism need to be employed.
IEC61000-4-4 defines the following in it's standard:
As a part of IEC61000-4-4 test, EFT pulses are injected into the power lines of the equipment under test, external interface connectors which include signals
1. Test voltage waveform that is applied to a system which is similar to the transients that are created during inductive load switching.
2. Also, the case where such transients occur when there is fact switching of load.
3. The test cases for both the above methods have been defined in the standard.
4. The waveform applied to the system as a part of EFT test will have low energy
5. The waveform applied to the system has a high amplitude (0.5 - 4 kV) @2.5KHz
6. The waveform has a short rise time
7. The pulses are applied to the system at some repetition rate (Like for example 100ms for a period of 2 seconds and these specifications depend on the standard your product prefers)
8. The current is low for the pulse that is applied
Other tests under EFT whose standards are derived from IEC61000-4-4:
EN 55024 - for IT equipment
IEC 61547 - Lighting equipment
To pass EFT tests:
1. Use Ferrite bead in series and capacitor to ground to filter out the transients
2. Use TVS diodes at the input of the connector
3. Take appropriate measures in the layout like avoid any routing near the connector and the signal input at the connector should see the decoupling capacitor.
4. Whatever energy that comes to the circuit through the connector should be routed back to the connector with a shortest and low impedance path.
]]>
0 Comments