Assembling a complete test system for immunity and emissions requirements is a challenge because each component has to complement as well as operate in harmony with the others. The key to a test system to provide the required tests and reports is the software. But which software features and functions do you need for your immunity and emissions testing?
The most important feature of EMC software is the capability to control a wide variety of instruments and platforms, said Michael Cagney, vice president of sales at Schaffner EMC. You also need the capability to generate seamless, customized reports. To meet both requirements, it is necessary to have system software with the appropriate drivers to control the hardware and autocalibrate the instruments.
Today’s EMC testing takes longer, especially for companies that perform batch testing with five to 10 tests per batch, said Mr. Cagney. To ensure the tests occur correctly and accurately requires an automated sequence and verification of the equipment-under-test (EUT).
An EMC test-software package also should run under the Windows 95 or NT operating systems, support international EMC regulations, and provide dynamic linking to hardware driver modules, said Joe Sivaswamy, president of EMC Automation. Additional general requirements include a network interface for EUT monitoring and custom applications and a user-friendly operator interface.
Emissions Test
For radiated and conducted emissions, you need on-line documentation, instrument correction factors, graphics capability, simultaneous display of measurements, and control of external devices, said Cliff Morgan, product marketing manager at Tektronix. The on-line documentation function should have a context-sensitive help feature to save time when you are learning to use the software.
Graphics are needed to show limit lines and data in different colors for easy identification, continued Mr. Morgan. Simultaneous display of measurements such as peak, quasipeak, and average is useful because it allows you to see the relative values during a test. For example, you may want to create a continuous line plot of the peak data, then show selected quasipeak or average readings.
The software should be able to provide the complete spectrum of emissions from a device, said EMC Automation’s Mr. Sivaswamy. This is almost always done using peak detection for the fastest possible results. The software must have a utility to reduce this data and generate a signal list by comparing it against a known limit.
A significant amount of data is acquired by test receivers in the peak mode, but generally it is not desirable to test all data points with the quasipeak and average detectors, said Mr. Morgan of Tektronix. It is more useful to divide the data into a specified number of subranges, such as 20, which allows the peak in each frequency subrange to be identified. Then you can run quasipeak and average detector measurements on the highest amplitude points.
The capability to control external devices also is important when making radiated emissions measurements, such as controlling the antenna mast and the device-under-test (DUT) turntable, said Mr. Morgan. For proper operation during conducted emissions measurements, you must be able to switch the receiver input between the high and low leads of the line-impedance stabilization network.
The EMC standards specify a variety of devices that are used to measure the desired emissions, said EMC Automation’s Mr. Sivaswamy. The standards call for the use of different transducers, including antennas for several frequency ranges, and LISNs and current probes for conducted EMI measurements.
Figure 1 shows the various instruments that must be controlled by software. The software lets you perform tests to CISPR recommendations or any required international standards. It should measure, store, and perform analysis of the data. Drivers for controlling antenna masts and turntables also must be available.
Radiated emissions measurements at open-area test sites pose a special challenge because measurements must be made in the presence of ambient signals such as radio and TV stations and cell phones, continued Mr. Morgan. The software should differentiate between ambient signals and the DUT. This may include subtracting the ambient signals or graphing the ambient and DUT traces in different colors.
Emissions software should offer pre- and full-compliance testing to all EMC standards, said Joseph Heins, senior EMC applications engineer at Chase EMC. The software also should be accompanied with an operations manual so factory personnel can program and operate the test equipment.
Test libraries designed for each IEC standard are required for EMC testing, said Schaffner’s Mr. Cagney. As each library is accessed, test objects become available for insertion into your personalized program. Additional library routines also can be installed.
A good EMC software package contains a library of predefined tests and limit lines for common tests such as FCC Part 15B and EN 55022, said Tektronix’s Mr. Morgan. It saves you time because the setup work is done when you install the software.
The software also should let you define macros, said Mr. Morgan. The emissions software should include macros for acquiring raw data, adjusting data for correction factors, graphing the prescans of data, performing subrange peak reduction, performing quasipeak or average measurements at selected frequencies, and printing results.
Additional emissions software features to look for include the capability to lock out setups and results with a password; perform limit line editing, discrete frequency, and amplitude measurements; overlay previous data on existing scans, and run scans while correcting the data with different transducer factors and frequency ranges, said Chase’s Mr. Heins.
Immunity Software
Immunity software typically is a Windows-based package that offers compliance testing to the IEC, ANSI, and military standards, said Mr. Heins. The software should test for radiated or conducted immunity and:
Program test-equipment configuration files.
Control signal generators, spectrum analyzers, power meters, isotropic probes, and dual-band amplifiers.
Store test setup and results files.
Protect setups and results with a password.
Maintain a log of all IEEE and RS-232 transactions for debugging instrument driver files.
Perform discrete frequency and amplitude measurements.
Perform field uniformity calibrations per EN 61000-4-3-1997.
Apply different voltage levels to an EUT in different frequency ranges. For example, 80 MHz to 134 MHz @ 10 V/m, 134 MHz to 147 MHz @ 3 V/m, and 147 MHz to 1,000 MHz @ 10 V/m.
Test for swept or interleaved spot frequencies.
Access IEEE 488 or RS-232 instrument driver files.
Monitor, display, and adjust the resultant RF current when the bulk current injection or EM-clamp is used during conducted immunity testing.
Figure 2 shows a turnkey immunity test system. The degree of testing depends on the size of the test object. The system can range from a full-compliance conducted and radiated system complete with an anechoic chamber to a precompliance test cell. The system tests the EUT automatically and records the EMC failure data. The software also controls the rotation of the turntable and any options such as cameras.
A single software interface to control equipment for testing is an advantage when you need to run a variety of tests such as the IEC 1000-3-x, the IEC 1000-4-x, and automotive procedures, said Schaffner’s Mr. Cagney. This is made possible through the use of test libraries that are accessible from the main user interface. Each library contains the necessary interfaces and links for controlling and setting up the hardware.
The required immunity test software features include setups for test parameters, test range, leveling, data display for graphs or tables, and documentation, said EMC Automation’s Mr. Sivaswamy. The test-range setup should provide frequency stepping, manual or user-defined dwell time between steps, and a pause or skip option for selected ranges. Leveling lets you define test levels, output levels, and generator drive levels.
Immunity testing also should provide a calibration function, field uniformity measurements with up to 100 grid points, and step-profile generation for up to 10 levels, said Mr. Sivaswamy. Finally, the system needs a network interface, status monitoring, signal analysis, and computer-controlled video monitoring to complete the package.
EMC Test Software
Software Helps Automate
Radiated, Conducted Tests
The SW1003 Software for radiated and conducted immunity testing helps meet the IEC 1000-4-3 and 1000-4-6 requirements. It features automated calibration, testing, and report generation. Thresholding and closed-loop leveling for precompliance-equipment checks are offered. Test parameters are user selectable and include a manual or an automatic probe, an antenna, and EUT turntable positioning for radiated immunity testing. Automatic data acquisition is provided for eight digital and 16 analog channels. Amplifier Research, (800) 933-8181.
Test Software Measures
Uncertainty Values
AEsoft Uncertainty Software provides tools for determining and applying uncertainty to measurements. The software displays the uncertainty characteristics and frequency dependencies caused by antenna factors, receiver calibration, cable losses, and test- site calibration. It shows the contribution of each element to the overall uncertainty value. An application tool imports measurement data and applies the overall value for viewing in tables and graphs. A statistics tool supplies the calculations to determine the uncertainty for an element. Atkinson Engineering, (540) 347-5716.
Software Is Configurable for
Radiated, Conducted Tests
The CIS9942 PC-Based Software is used to configure immunity tests including bulk current and voltage injection for conducted measurements and chambers or TEM cells for radiated testing. It also offers automatic and manual failure analysis. An edit function helps create or change instrument drivers. Drivers for GPIB-based signal generators, power meters, field sensors, spectrum analyzers, and voltmeters are included. Data for radiated field strength, signal-generator output, RF power output, and monitoring instrumentation is displayed during field calibration and measurements. Chase EMC, (973) 252-8001.
Radiated Immunity Software
Works GTEM Systems
GSOFT™ performs radiated immunity measurements in a gigahertz transverse electromagnetic cell (GTEM) and is designed for testing to SAE, ISO, and IEC regulations. It runs under the Microsoft Windows environment and controls the test process via the IEEE 488 bus. Up to 100 grid points for the field measurement plane, tests for data collection and uniformity verification, and an interactive mode for failure analysis are supported. EMC Automation, (512) 258-9478.
Software Controls Instruments
And Supports Data Analysis
TILE/ICS is an integrated information system that controls immunity and emissions test instruments, supports data analysis, and provides test reports. The instrument control subsystem helps create standard and customized test profiles. The software has tools to send unique instrument commands as part of the normal test execution. It integrates results with a variety of data-base programs. A report-writing system works with most word processors and supports macro creation for customized formats. Quantum Change/EMC Systems, (703) 207-0344.
Single Interface Accesses
Immunity Test Libraries
Powerstar EMC is a Windows-based software package with a single interface to control and operate instruments for testing to all IEC 1000-3-x, IEC 1000-4-x, and automotive immunity requirements. Test libraries are accessible via the main user interface. Each library contains the interfaces and links for the required hardware. Test functions include enable, disable, abort-on-fail, ignore fail, graphing, printing, and branching. Systems can be configured to include RS-232, IEEE, and VXI instrumentation. Schaffner EMC, (973) 379-7778.
EMI Measurement System
Software Is Windows-Based
The 27120A EMI Measurement System performs pre- and post-certification testing. It incorporates the company’s EMC120 Windows™-based software package to help create and modify EMI tests. The software has paths for novice and advanced users; provides on-line help; stores and recalls test setups and data, and offers color graphs to display multiple scans and limit lines. Tektronix, (800) 426-2200, press 3, code 1006.
Software Measures Radiated
EMI Emissions to 2 GHz
The HP 85876B Commercial Radiated EMI Measurement Software controls test equipment and the measurement process. It performs EMI emissions tests from 30 MHz to 2 GHz for commercial, industrial, scientific, and medical applications. The software is compatible with Windows 3.1, 95, and NT 4.0. Data and graphics can be exchanged between spreadsheets and word processors with no additional scripting and programming. Test configurations and libraries for global EMC test regulations are included. Hewlett-Packard, (800) 452-4844.
Copyright 1998 Nelson Publishing Inc.
April 1998