Designing Products to meet International Regulatory Requirements

As Indian product houses gear up to design and manufacture products for international markets, a key requirement that product designers need to be aware of are the regulatory standards that the products need to comply to, to be able to legally ship to those markets.

In this article we share our experience at Tejas Networks of design, testing and certifying our TJ100 family of next-generation SDH/SONET products to meet worldwide regulatory standards.

Regulatory basics

The most widely recognized international regulatory marking is the CE mark, which, coupled with country-specific deviations, enable a product to be sold in most parts of the world, with the exception of North America.

The CE mark is a combination of standards defining product safety and Electromagnetic Compatibility (EMC) requirements. For information technology products, the CE mark requires conformance to IEC60950 for Safety and a collection of EMC standards (EN55022, EN55024, etc).

North America has additional EMC requirements as defined by the FCC standards.

IEC60950 specifies safety requirements for products with rated voltage less than 600V. This standard is intended to reduce the chances of death, injury or property damage due to hazards in the areas of electrical safety, energy hazards, mechanical safety, heat, fire, radiation and chemical hazards.

The EMC standards specify emission limits for internally generated high frequencies and immunity requirements from radio frequency interference from the external environment, which may cause product malfunction.

Design for Compliance

From a designer’s perspective, regulatory requirements have a significant impact on the design of an electronic product, and they have to be dealt with as an integral part of the design process. However, very often, they are not considered until late stages in design completion and testing, and result in substantial modifications to the product, resulting in time and cost overruns.

Some of the key aspects influenced by the Safety specs are the following:

• The enclosure must prevent access to hazardous moving parts and parts with hazardous voltage or energy levels, even during abnormal operation or product failure.
• The design must protect users from electric shocks and energy hazards by adequate insulation between high-voltage circuits and parts which users will have access to.
• Adequate insulation to be provided between low-voltage circuits and circuits which connect to external telecommunication networks, which could be subject to over-voltages.
• All safety critical components (e.g., switches, fuses, motors, transformers, etc) must be UL-approved.
• Material used for enclosure, internal and external parts (PCB, cables, etc) should have appropriate flammability ratings which are resistant to fire and prevent fire spreading
• Thermal design should ensure that temperatures within and on the surface of the product do not become too high to cause burns or start fires, even in case of failures of fans and other cooling devices.

EMC specs influence product design in the following ways:

• The enclosure should be conductive and should provide an effective shield against signal radiation. Apertures and ventilation holes should be sized appropriately to provide effective shielding.
• PCB stack-up and layout play a key role in controlling EMC. The key objectives in a multi-layer PCB design are:
o Signal layers should be adjacent to and closely coupled with their ground planes
o High-speed signals should be routed in buried layers located between planes. In this way planes act as shields and contain radiation from high-speed traces.
o Adequate number of ground planes and proper ground plane design to provide current return paths, proper separation of digital and interface grounds to reduce common-mode interference
• Filtering – all interfaces, including mains, should be shielded, grounded and filtered adequately using chokes and suppression ferrites to suppress common-mode noise escaping through cables.
• If the equipment is to be used in environments that are subject to high-energy surges, then adequate surge-suppressors are required on all applicable interfaces.

Compliance as part of the design process

To achieve early success, regulatory compliance has to be an integral part of the design & test process for a product design team. At Tejas Networks, it starts by defining the compliance goals for the product as part of the product requirement specs. An extensive set of design recommendations guide engineers through the design creation process.

Prior to prototype manufacture, the designs (schematic, layout, enclosure) are reviewed thoroughly for EMC and Safety compliance.

With the availability of the first prototype, pre-compliance testing becomes one of the early test steps. It is important that the prototype is tested for worst-case conditions (fully-loaded traffic conditions, all interfaces active, proper cabling setup, high amount of software activity) to get accurate information of design marginalities and to cover lab-to-lab calibration variances.

Regulatory test infrastructure in India

While being far from adequate, there is a moderate infrastructure in India to provide product designers with regulatory test support during design, and certification testing prior to production.

Some of the notable test centers available are the ERTL labs in all key metros, SAMEER in Chennai, and testing labs of several public sector units such as BEL and HAL. These labs can be used for both pre-compliance (experimental) and certification testing.

Almost all key international certification agencies – TUV, CSA, UL, etc, have offices in India and can be used for product certification. Many of them are also equipped with labs that provide compliance test support to varying extents.