Crosstalk is one example of this test area. In this process, a signal is coupled from one line into a parallel line – as is the case when tapping into telephone lines.
Crosstalk is also the reason that, for example by switching large loads, several kV of energy can act on the cables of your device. This effect is simulated by the burst test. If a lightning strike occurs in the power grid, a very strong energy wave propagates on the power grid. This phenomenon is simulated by the surge test. In case of long cables, however, electromagnetic fields can also couple into the cables and generate high-frequency interference energy; this effect is also simulated in the EMC. This area includes short-term voltage fluctuations or failures in the supply network.
The standards and procedures in this area include the following:
- IEC 61000-4-4 – Burst
This test with recurrent fast transients is a test with pulse packets (bursts) consisting of a number of fast transient electrical disturbances coupled into power supply, control, signal, and earth or ground connections of electrical devices. Characteristic of this test are the high amplitudes, short rise time, high repetition frequency and low energy of the transients. The test is intended to demonstrate the immunity of electrical devices to certain types of transient disturbances, such as those arising from short-term switching operations, interruption of inductive loads or bouncing of relay contacts.
- IEC 61000-4-5 – Surge
A surge is a transient electrical current, voltage or energy wave propagating in a line or circuit and characterized by a rapid rise time and a subsequent slow fall (examples include significant switching surges due to switching of capacitor batteries, short circuits and faults with arcing in the plant's grounding system, or a lightning strike into the circuit). Air gaps, gas arresters or varistors are used to protect against this destructive phenomenon with peak currents of several hundred amperes.
- IEC 61000-4-6 – Conducted high frequency
This test simulates the coupling of electromagnetic disturbances for example from high-frequency radio transmitters into the connecting cables of the test object in the frequency range between 150 kHz and 80 MHz. In this process, the disturbance is impressed as a voltage via a coupling network onto all lines that are suitable for coupling one after the other, and the reaction of the test object is monitored. For frequencies above 80 MHz, the test method according to IEC 61000-4-3 is used, since generating electric fields in the frequency range of up to 80 MHz is very expensive and complex (the wavelength for a frequency of 150 kHz is 2 km). Very large antennas are required to couple such fields, which in most devices are only formed by the long connecting cables.
- IEC 61000-4-11 – AC grid fluctuations
The voltage quality of the grid voltage is essentially affected by the quality of the generation, by impacts during transmission and by reactions of the consumers themselves. The consumer (customer) is obligated by the operator of the electrical grid to keep reactions of his electrical installations within permissible limits in order to avoid affecting "neighbors". Disturbances can be caused by defective devices or devices that do not comply with the standards. EDP and telecommunications systems are particularly sensitive to voltage quality. A "dirty" power supply system can cause frequent system crashes and hardware failures. There are various measures to remedy this. The simplest measure with the least effect is to use additional line filters. An uninterruptible power supply (UPS) also provides protection against power failures. The most effective measure is a voltage stabilizer or power conditioner, although uninterruptible power supplies sometimes have the same functions. Arc short-circuits in the extra-high voltage grid with 220 kV and 380 kV, typically in overhead lines, like those caused for example by a ground fault, can usually be eliminated through an automatic restart of 0.3 s. This causes a brief voltage drop at the end user’s, which is noticeable in the form of brightness fluctuations in incandescent lamps.
- IEC 61000-4-16 – Audio frequencies
This test is intended to demonstrate the immunity of electrical and electronic equipment to conducted asymmetric disturbances such as those caused by currents in supply lines and by leakage currents flowing back into the earthing/grounding systems. Except in industrial installations, actual disturbances caused by the above-mentioned disturbance phenomena are relatively rare. The disturbances are typically generated by power supply systems with their fundamental frequency and their harmonics and inter-harmonics, as well as by power electronics and their filters. Coupling the source of the disturbance with power supply, signal, control and communication lines of the test object ensures that the disturbances are transmitted to the connections of the device under test. An example of such disturbance are ground loops in a HiFi system.
- MIL-STD-461 CS115 – Impulse Excitation
This requirement serves to prove the functionality of the test object in the case of steep-flank pulses such as those caused by a lightning strike, switching large inductive loads such as a gun motor, or an electromagnetic pulse (EMP).
- MIL-STD-461 CS116 – Damped Sinusoidal Transients, Cables and Power Leads
In contrast to CS115, which stimulates natural resonances, this requirement is to simulate the waveform as an attenuated sine wave. In cables, stimulation with steep-flank pulses can cause damped sine waves in resonances. A wide frequency coverage (10 kHz to 100 MHz) is included in this process in order to account for as many phenomena as possible and to demonstrate high immunity to disturbances.
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Carsten Möller Carsten Möller
Head of EMC Laboratory