A Program for Successful Testing of Network Equipment Building Systems

A Program for Successful Testing of Network Equipment Building Systems

Compliance with test requirements defined in GR-1089 and GR-63 is no problem for those who are prepared.

The first step in preparing for a successful NEBS compliance program is to review the test requirements as defined in Telcordia Technologies's standards GR-1089, "Electromagnetic Compatibility and Electrical Safety—Generic Criteria for Network Telecommunications Equipment," and GR-63, "Network Equipment Building System (NEBS) Requirements: Physical Protection." Each of these documents contains absolute requirements, objectives, and conditional requirements (taken together, called R&Os) which are itemized in checklist tables found in the specifications. These tables help determine which tests are

Once the R&Os checklist is complete, the compliance engineer can begin to develop the GR-1089 and GR-63 test procedures, or approach a test laboratory to develop them, for review by the regional Bell operating company (RBOC) or other service provider. The procedures will require a review of the equipment under test (EUT) in order to determine its worst-case configuration. The worst-case configuration for one test is not necessarily the worst-case configuration for all tests, so a thorough understanding of each test setup is crucial.

If enough EUTs are available, it is advisable to make a system for each scenario available for parallel testing in order to minimize time spent reconfiguring systems for each required test. Two configurations at least are recommended: a fully loaded and functioning system for operational testing, and a unit with operating fans and nonfunctional cards to constitute a full fuel load for the fire test.

GR-1089 Test Regimen

The GR-1089 standard comprises some half-dozen major test groups: electrostatic discharge (ESD; Section 2), radiated emissions and radiated immunity (RE and RI; Section 3), conducted emissions and conducted immunity (CE and CI; Section 3), lightning and power cross (transients; Section 4), power induction (Section 5), electrical safety (Section 7), and bonding and grounding (Section 9).

Preparation for each test group is important. For GR-1089 testing, all EMI and transient protection devices—EMI gaskets, filtering, connectors, and so forth—must be properly installed and checked prior to the start of any test procedure. The proper operation of the unit must be defined, and testing personnel must understand what it is. This is critical for determining the pass-fail criteria for the immunity and transient tests. In addition, all ports must be properly terminated and functioning.

ESD. ESD tests require that the EUT be operating during application of as many as 40 discharges at all physically accessible locations. This calls for a clear understanding of the physical configuration of the test device in operation. If the unit has a panel or door that is normally closed during operation, the door should be closed for this portion of the test. ESD test points should be detailed in the test procedure. They can be quite numerous. All test points need to be checked for compliance to Section 2 of GR-1089.

The unit being tested also must operate after the application of discharges to areas that are accessible during maintenance and repair. This specification requires testing with the doors open. Again, the test points need to be clearly defined in the test procedure and referenced in a maintenance manual or user guide. There is no requirement to test areas that are not accessible during normal operation or maintenance. If the EUT fails to meet any of the ESD requirements, compliance with GR-1089 can be achieved by the placement of warning tags on the unit.

Radiated immunity testing is required to be performed in a room that will not affect the uniformity of the radiated field. Such rooms would be qualified to EN 61000-4-3 or MIL-STD-461D/E. If a semianechoic room is used, a small patch of ferrite tiles can be placed on the floor to meet the EN 61000-4-3 field uniformity requirement. This recipe is an important time-saver because it eliminates the need to disassemble and move equipment to a new test facility for immunity testing after radiated emission testing is completed. In fact, all GR-1089 testing can be performed in the semianechoic chamber if so desired.

When radiated immunity and emissions testing is conducted properly, all support equipment (except antennas) is outside the chamber in a control room. This requires cable runs of 30–40 ft for a semianechoic chamber and up to 50 ft for
an OATS.

CE and CI. For the conducted tests, each type of data and signal port needs to be defined and tested separately. The distinctions should be clearly delineated in the test procedure. Ac and dc power lines also must be tested. (Equipment on the test client's premises that is powered by alternating current will be required to meet the conducted and radiated emissions requirements of the FCC.) Analog voice-band leads have a separate CE limit.

The pass criteria for radiated and conducted immunity tests vary depending on equipment functionality within the network. Typical compliance requires that the equipment be manually reset, reset itself, or operate continuously.

Testing for NEBS compliance with the R&O of GR-63 involves five major areas: heat dissipation, operating temperature, transportation and storage, fire, and earthquake. Preparation for each of these test groups is important.

Some RBOCs demand that altitude testing be performed in addition to the test to establish compliance with temperature and humidity requirements. The altitude component makes the test more difficult to pass than might be supposed at first, because it requires that a large environmental and vacuum chamber be employed.

The crates are mounted on a vibration table and subjected to a low-grade profile in order to simulate a typical on-off loading experience and truck ride.

The office vibration test normally performed sequentially with the earthquake test is also required. The purpose of this test is to verify unit or system operation under a lower-level, longer-duration fatigue environment.

While NEBS compliance testing can be a long and problematic process, following the foregoing suggestions and choosing a qualified test laboratory with knowledgeable personnel can make the road smooth. Compliance can be achieved at each test milestone. The safety and fire tests ought to have top priority. Once those challenges have been met, all the other requirements will most likely be satisfied with few or no further system modifications.

Having access to an experienced testing or consulting organization that possesses knowledge of all aspects of NEBS is of great value when redesign or compromises are required. Such an organization is especially valuable early in the equipment design phase, when it can offer guidance that will prevent any need for time-consuming redesign later at the testing stage.

James Press is national EMC director for National Technical Systems (NTS; Boxborough, MA). Press is responsible for all the company's EMC technical issues and developments, including expansions of EMC test and engineering capabilities. He can be e-mailed at jimp@ntscorp.com.

Mark Betts is EMC lab manager responsible for all EMC testing at NTS's facility in Tinton Falls, NJ. Betts is certified as an EMC test witness engineer and as a technical construction file assessor. He may be reached via e-mail at markbetts@worldnet.att.net.

John Ngo is compliance manager at NTS in Fullerton, CA. Ngo has more than seven years' experience in EMC design and testing, and more than three years' experience in the product safety arena. He can be contacted via e-mail at johnn@ntscorp.com.

Mike Cantwell is EMC manager of NTS's newest facility in Plano, TX. Cantwell, who is NARTE certified and has more than 10 years of EMC testing experience, oversaw expansion of the facility into a fully compliant GR-1089 and GR-63 test laboratory. He receives e-mail at mcantwell@ntscorp.com.