Automated Component Level EMC Test Facility

Abstract

An EMC test facility has been developed and constructed by John Deere at the Product Engineering Center, Waterloo, Iowa. This facili­ ty has fully automated the radiated emissions test and the radiated susceptibility test. With this capability and the centralized organiza­ tion of the equipment, the time to conduct a complete EMC test has been reduced by 70 percent compared with manual methods. A typical product can be fully tested for both emissions and susceptibility in seven hours. This paper will describe the hardware and software im­ plemented at this facility. Automated EMC Test Facility automated facility had become a reality. Although 2Vi years had pass­ ed, only 1 Vi man-years was expended to make the facility functional. Seven hours, that is how long it takes to conduct a complete EMC test from setup to report generation of a typical product. The facility shown in the block diagram of Figure 1 and in the photograph of Figure 2 has the following capabilities: 1. Frequency coverage of lOKHz to 1GHz 2. Real time monitoring and control of the RF fields and the device under test (DUT) via the IEEE-488 bus and the HP-3497A data ac­ quisition/control unit. Introduction The development of a large number of new electronic products to be offered by John Deere has required that EMC testing be done by a fully automated test facility. An internal specification was written to meet or exceed regulatory (FCC Part 15) as well as recommended (SAE standard J551 and SAE practice J1113) EMC requirements. Us­ ing this specification, the evolution of the EMC test facility began in the first quarter of 1979. By the second quarter of 1981, a fully 3. Centralized control from the HP-9845S desktop computer. 4. Automatic report generation and archiving using the HP-9872A plotter, a line printer and eight inch flexible disks for mass storage. 5. Storage of calibration data and correction factors. This has increas­ ed measurement accuracy and test repeatability. Figure 1. Automated EMC Test System Block Diagram 3 6 4 6. 16’ x 20’ x 8’ anechoic chamber with pyramidal cones on the walls, floor, and ceiling. The minimum reflection attenuation is 20 dB at 100 M Hz and 40 dB at 1 GHz. A 4’ x 10’ copper ground plane is provided to support the device under test (DUT). See Figure 3. 7. Two video monitors, both with zoom, pan and tilt capability. 8. Shielded or single plate stripline test cells for products which are less than 10 cm on any side. Most of the products tested are in this category. Figure 2. Automated E M C Test Facility Figure 3. Anechoic Test Chamber with a Shielded Stripline In Place Radiated Emission Testing The system used for automating EMI measurements and data col­ lection is an Ailtech (now Eaton) Series VII system. This system is comprised of two field intensity meters, the NM-17/27 A (10 KHz to 32 MHz) and the NM37-57A (30 MHz to 1.0 GHz). Selection of the pro­ per field intensity meter as well as a programmable attenuator between the meter and the selected transducer is performed by the CIU7 con­ trolled input unit (inputs units A and B). The CP-7 acts as a program­ mable controller for both the receivers and the controlled input units. The basic operating EMI system software allows the operator to select from a menu of the main program all necessary functions to operate the CP7, as well as all necessary data manipulation and report generation. The operator has the ability to write, edit, store, list, recall, and execute data necessary to operate the CP-7 from this menu. There are two levels of emission testing, a general test, which re­ quires minimal EMI test experience since it uses a predefined scan algorithm, and a complex test, which requires a trained operator because it allows definition of the scan algorithm. The predefined scan algorithm is generally used to conduct a preliminary emission test. A more detailed analysis of the emissions can be obtained entering “yes” in response to an operator prompt, “Do you wish to define the scan algorithm?”. The operator is then re­ quested to provide values for the eight scan segments, each consisting of the following parameters: