Product reliability has always been of uppermost importance at Phoenix International, an electronics company owned by Deere & Co., the manufacturer of John Deere farm and garden equipment. Heightened customer expectations have emphasized the importance of both equipment reliability and durability.
Phoenix International designs and manufactures OEM electronics for many agricultural and commercial applications, including John Deere. To ensure that its products perform properly in different environments and to minimize unforeseen field failures, the company has adopted a formal design validation program.
The Implementation
Design validation is the process of environmentally stressing any given component or system to force a failure. These stresses often are defined in industry specifications derived from the product’s projected end environment and developed or distributed by organizations such as the American Society of Agricultural Engineers (ASAE), the Society of Automotive Engineers (SAE), the International Special Committee on Radio Interference (CISPR), and the International Electro-technical Commission (IEC). Some companies develop their own internal specifications that dictate how products must perform. The same requirements serve as specifications for component or subassembly vendors.
When Phoenix International hired me as its design validation engineer for the Springfield, IL, facility, the North Dakota plant already had a successful Design Validation Department. With a new building under construction, I was assigned the responsibility of designing the new laboratory and implementing the validation program.
Detailed construction of the laboratory included working with the facility manager to design electrical power distribution and ventilation. Computer network drops were placed, distribution of deionized water for environmental-chamber humidity was arranged, and an isolated concrete pad for vibration equipment was poured. Now, we were ready to begin validating the design of new products with a series of tests.
Accelerated Life Tests
Design validation tests cover every aspect of a product’s operation. One of the most demanding is the 100-day accelerated life test, a version of the industry’s highly accelerated life test (HALT). During this process, we can vary the temperature from -70°C to +175°C and humidity from ~0 to 95%. In association with the environmental profile, we cycle the input voltage. All this is accomplished on a very strict time schedule controlled by LabVIEW software from National Instruments running on a standard PC using Windows 98.
An environmental chamber runs a preprogrammed temperature/humidity profile. A 4-bit digital signal is acquired from the chamber via a National Instruments acquisition module to allow the test designer to coordinate all aspects of the test, including environmental cycling, voltage cycling, and measurements.
To know if stresses are affecting the product, a system monitors its operation. The setup is complex because at least six products of the same type are tested in parallel to provide a better statistical sample and remove the possibility of error in the test setup.
Test sequences depend on the products being tested. Output lines are monitored, and input lines are stressed appropriately. When possible, actual loads are incorporated into the test.
The philosophy is to ensure that the test setup is as close to the real-life environment of the product as possible. For example, if an engine controller is tested, the fuel injectors, a production control panel, and relays are used.
ESD Testing
Electrostatic discharge (ESD) testing is a part of design validation. We use a Schaffner NSG 432 ESD Gun to pulse the product as it rests on a special surface. This setup is per the IEC 1000-4-2 standard. A pulse from -25 kV to +25 kV can be generated with various source impedances. The test surface is connected to ground directly or through a 470-W resistance, and the station and operator are on a metal ground plane during the test.
The ESD test can uncover problems ranging from fundamental design flaws to faulty components. In many cases, components could pass incoming inspection and even pass the standard functional tests. However, substrate contaminants or bad lead junctions represent warranty claims waiting to be realized.
BCI Tests
Bulk current injection (BCI) testing to industry standards also is part of our design validation program. In this test, we try to induce a signal into a cable harness and measure the opposite end of the harness to determine how much of the signal is actually conducted. We use a circular injection probe manufactured by Fischer Custom Communications with an RF amplifier from Amplifier Research. At the opposite end of the harness, we have a spectrum analyzer manufactured by Agilent Technologies. The system is on an isolated ground plane to remove any possibility of external interference.
GPS Reception Problems
Several of our products use global positioning system (GPS) receivers to determine their locations during normal use. To validate the design of the GPS function in those products, we must access GPS signals in our design validation area.
However, we had difficulty because our large building with its metal roof significantly degraded the incoming GPS signals. We tried a splitter to divide the signal into several streams, but experienced crosstalk and signal degradation. A GPS reradiator kit consisting of a GPS antenna, a linear amplifier, and a rebroadcast antenna, seems to have corrected the difficulty.
Acknowledgement
I appreciate the support I received from my direct supervisor, Bob Mallett of the Fargo division, as well as the others in Phoenix International and John Deere management who entrusted this project to a young engineer. They provided guidance when I needed it and were pivotal in affording me freedom to implement the design validation program in Springfield.
About the Author
Brandon M. Keafer, a design validation engineer at Phoenix International, recently graduated from the University of Illinois with a degree in electrical and computer engineering. Phoenix International, a John Deere Co., 5300 Rising Moon Rd., Springfield, IL 62707, 217-483-9050, e-mail: [email protected].
Published by EE-Evaluation Engineering
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December 2000