Now that you are sure you will sell electronic products overseas, you may want a crash course on the immunity issues. You need to understand what testing procedures and equipment will help you prepare your product for the European Union (EU).
The EU’s EMC Directive requires all electronic and electrical products to be tested for immunity to both man-made and natural phenomena. It also requires that products not emit unintentional signals that may interfere with the reliable operation of other products.
Compliance with the EMC Directive requires that products be tested in accordance with European Norms (EN) issued by CENELEC, the European committee for electrotechnical standardization. The immunity ENs are developed by the International Electrotechnical Commission (IEC); and as of January 1997, it began using the same numbering scheme as the EN standards. For example, IEC 1000-4-2 changed to IEC 61000-4-2, the same as the EN 61000-4-2 standard for electrostatic discharge (ESD).
The immunity standards developed by the IEC have equipment requirements that are significantly different from the emissions standards and can present problems for U.S. manufacturers that want to sell products in the EU. Choosing the right equipment is just as important as understanding the applicable test procedures. The end result is being able to apply the CE Marking to your product.
The Immunity Standards
There are many immunity test standards available and more coming in the near future. Some of the frequently used test standards presented here address electrostatic discharges, radiated electromagnetic fields, electrical fast transients and surge voltage immunity. Look for information on additional immunity standards in future issues of EE.
IEC 61000-4-2 Electrostatic Discharge Requirements: The objective of this standard is to establish a common reference for evaluating the performance of instrumentation when subjected to ESD. The discharge is checked between people and objects near instrumentation or discharges transmitted directly into the instrumentation.
A typical event described in IEC 61000-4-2 simulates a person with a metal object in hand, such as a screwdriver, approaching a piece of equipment. The standard specifies an air discharge mode and a direct-current discharge mode.
In the air discharge mode, a spark from the test probe of the ESD generator is emitted toward the equipment under test (EUT). The test probe must provide adjustable charging to 8 kV.
The direct-current discharge mode requires an impulse released from the ESD generator while the tip of the generator’s probe contacts the EUT. For this mode, the generator should provide an adjustable voltage to 4 kV.
Another method is the indirect approach that simulates an ESD event that causes a radiated field to be emitted in the vicinity of the equipment. Testing is performed with vertical and horizontal coupling planes.
Current standards require discharges to be made to the edge of the vertical plane and to the surface of the horizontal plane. A discharge to the horizontal coupling plane causes a horizontally polarized field to be radiated into the EUT.
A vertical coupling plane is positioned in front of the EUT and a discharge is made to the edge of the vertical coupling plane. The discharge causes a vertically polarized field to be radiated toward the EUT. All four sides of the EUT must be tested in this manner.
The equipment needed to perform this testing includes a test fixture and an ESD simulator that charges to a minimum of 8 kV.
IEC 61000-4-3 Radiated Electromagnetic Field Requirements: This standard tests the susceptibility of electronic products to radiated EMI fields. For example, it checks how a computer performs when in close proximity to an antenna radiating energy.
The standard states the levels of radiated energy a product should tolerate and still perform correctly. For example, products should withstand electrical and magnetic interference in a strong electromagnetic field generated by a portable radio transceiver, fluorescent light, industrial welder or local TV antenna.
Test procedures and test levels are established by the standard and used as a common reference for the test equipment. The testing frequency is between 80 MHz and 1,000 MHz with 80% amplitude modulation and located at 3m from the EUT.
The test equipment needed to meet these requirements includes a signal generator with a frequency range of 26 MHz to 1 GHz that is used to drive power amplifiers. The power amplifiers must be capable of 100 W minimum and 500 W maximum from 26 MHz to 220 MHz and 50 W minimum from 220 MHz to 1 GHz. A transmit antenna for the 26-MHz to 1-GHz frequency range is needed and may be a biconical for the low end and log periodic for the high end of the spectrum, or a biconilog-type antenna for the whole range.
An isotropic field-strength probe and meter also are needed for verifying energy field flatness. Testing may be conducted in an anechoic chamber with a turntable for the EUT.
IEC 61000-4-4 Electrical Fast Transient Requirements: When an inductive load such as a motor is switched off, electrical fast transients (EFT) known as spikes or bursts can be generated. This arcing occurs between the contacts as the switch is opened.
Initially, arcing happens at a low voltage and high frequency when the contacts are close together, and then at a high voltage and low frequency as the contacts separate. Coupling of the EFT into electronic devices occurs when power cables handling high currents run in close proximity to power, data or I/O cables.
A typical burst is made up of single spikes with a maximum amplitude of 4 kV when coupled onto power supply lines and 2 kV when coupled onto I/O lines. Each pulse within the burst has a 5-ns rise time and a 50-ns pulse width.
The burst generator and a capacitive coupler are typical equipment for testing EFTs. For power lines, the transient is coupled onto the affected lead with a 33-nF capacitor and decoupled with a filter to direct all the transient energy to the EUT.
Transients on signal and control lines are coupled capacitively using a 1-m long clamp. The upper portion of the clamp wraps around the cable and attaches to the generator signal lead. The lower part connects to ground.
IEC 61000-4-5 Surge Immunity Requirements: Surges occur on the AC power lines as a result of switching operations in the power grid and from nearby lightning strikes. The standard defines immunity test methods and recommended test levels for equipment. It describes the unidirectional surges caused by high-energy disturbances on the power and interconnection lines.
Switching transients can be caused by power-system switching, short circuits or resonating circuits such as thyristors. Lightning-induced transients come from high voltages and currents injected through several conducting paths in a system due to a direct strike on the system’s power lines. An indirect lightning strike also can generate transients in equipment.
The main parameters of the surge defined in the 61000-4-5 standard include a voltage impulse waveshape of 1.2 µs on the rising edge and a 50-µs time to half value, with a maximum peak amplitude of 4 kV at the open circuit. A current impulse has a waveshape of 8 µs × 20 µs at short circuit with a maximum peak amplitude of 2 kA.
If the surge is applied to a communications line, the voltage impulse is a waveshape of 10 µs × 700 µs with a maximum peak amplitude of 4 kV at open circuit. The short-circuit current can be as high as 2 kA. Testing requires a combination waveform surge generator, a coupler, a decoupler for I/O and data lines connected to the measuring equipment.
References
1. IEC 1000-4 Series Standards Overview, Test Equipment Corp., 1995.
2. KeyTek Application Note, EMC Compliance, KeyTek Division of Thermo Voltek, July, 1996.
Copyright 1997 Nelson Publishing Inc.
April 1997