Breeze Through Compliance Obstacles With EMI/RFI Test Software EMC TestSoftware Comparison Chart

The flood of requests for test time at independent test labs continues, bolstered by the need to apply testing schemes similar to the European Union’s (EU) harmonized standards. These procedures require that products be certified before they enter the common market. As a result, test labs are backed up several months with the flood gates wide open and no slowdown in sight.

One way to meet compliance regulations and keep scheduling problems at a minimum is to purchase your own EMC test facility. Unfortunately, it is a considerable investment in equipment and personnel that most companies cannot or do not want to make.

Another option is to keep track of your design development and any potential EMC problems by performing the necessary precompliance testing in-house. Then when ready for compliance testing, your product will breeze through in a minimum of time and charge.

Several EMC test-equipment manufacturers provide hardware and software solutions to help you perform precompliance testing. Some even offer software to automate the testing. But do you know what the most important features of EMC precompliance software are?

The features to look for in EMI/RFI test software, according to Joe Sivaswamy at EMC Automation, include:

• Modular design to accommodate additional instrument drivers.

• User-definable correction factors for cable loss, transducer factors and limit-line entries.

• Computer control of turntables, towers and sweeps of the mast.

• Data-reduction techniques that limit data points.

• Automatic identification of ambient signals.

• A manual interactive mode to update existing data files.

More specific recommendations for automated EMC test software depend on what standards you use. For example, several companies such as Amplifier Research offer packages to help you test to the requirements of the immunity standards (see the comparison chart).

The SW1002 Electromagnetic Field Immunity Test Package from Amplifier Research is a stand-alone program that runs in a Windows™ environment, supports automated immunity testing and data collection and provides a report-generation function. It performs 16-point field-uniformity calibration and immunity testing, uses selectable test parameters and has an E-field failure threshold mode for precompliance investigations of equipment susceptibility. Closed-loop leveling for MIL-STD-461 or IEC 801-3 type troubleshooting also is incorporated.

First-time users of immunity test software will be pleasantly surprised by how easy it is to run automated testing. Many of the programs use graphical interfaces that accommodate specific tests such as specified in the IEC 1000-4-3 standard.

For many software packages such as the GSOFT™ immunity program from EMC Automation, you simply create a file and select a test sequence and a test method in the leveling setup procedure. Before beginning the immunity tests, you are led through a series of questions to identify the test equipment, followed by a calibration procedure. You can add, remove and change items such as leveling and graphing setup selections. You also can split frequency ranges into sub-ranges and change the field level of the power output.

For emissions testing, you should look for a flexible and intuitive software program. It should lead you through a predefined testing procedure but not so rigidly that it prevents custom- tailoring.

For example, when performing quasipeak or average testing, look for software that creates a suspect list of signals that is above a specified threshold and that you can edit before performing measurements, said Cliff Morgan at Tektronix. A test-setup menu should give you the opportunity to specify all relevant spectrum-analyzer settings, such as the overall frequency range, input attenuation, reference level, subrange frequencies, resolution bandwidths and sweep speeds. All correction factors and limit lines must be user-definable, he said.

Some programs have features to help you make the most of your time. For example, before starting a quasipeak or average measurement, packages such as the HP 85875A Conducted Emission Test Software from Hewlett-Packard “tune and listen” before measuring. It helps you avoid unnecessary measurements by zooming in on a signal and differentiating between an ambient radio or TV station and an equipment-under-test signal.

For broadband signals, the HP software uses a stepped or swept measurement over a frequency span. The recorded peak, quasipeak and average amplitude data are automatically recorded in the signal list.

The right software also reduces your test time and increases measurement throughput. For example, a spectrum search feature quickly identifies frequency segments that are occupied by suspect-device emissions. The software measures only in these occupied frequency segments, skipping unoccupied segments of the spectrum.

Superior software provides graphical representations of data and compares the EMI levels to the test limits of turntables and tower positions, said Mr. Sivaswamy. The test-equipment lists and setup schematics help you to quickly automate your testing process. They make editing and creating tests simple point-and-click operations.

A sorting option for data tables is another important feature. You can group information with reference to other data and display it in a logical fashion such as by ascending frequency or by turntable position.

The software you select also should include test configurations and libraries for EMI test regulations, such as the European Norms, FCC part 15 and the Japanese VCCI standards. It should have test configurations with the appropriate frequency ranges and test sequences, and have generic setups including the required configurations for screen rooms or semi-anechoic chambers.

Report customization is another important feature because it helps you select and organize parameters that are important to you. You should have the capability to port data from different test files into one report for comparison purposes.

Some reports let you compare data from different lists with Boolean search functions including AND, OR and NOT-AND. For example, a list containing ambient signals can be compared to another list containing ambient signals with device emissions. Signal lists can be derived that only have ambient signals or that just have device emissions that are suspect.

How to Find the Right Software

With many programs on the market today, a comprehensive search for the right software could take some time. To help you zero in on the best prospects for your needs, check the EMI/RFI Test Software Comparison Chart that accompanies this article. It shows you the features available including tests performed, standards supported, operating systems used and report-generation capabilities provided for a variety of software.

April 1997