From an electronics systems viewpoint, the typical automobile today looks very much like an airplane. So it’s not surprising that some automotive tester requirements are very similar to avionics subsystems testers of the past.
Factors that impact testing requirements are product safety and the need to demonstrate that a subsystem operates under the conditions that it experiences in the automobile. Avionics manufacturers have dealt with these circumstances for years. But when coupled with the very high production rates found in the automotive industry, the need to test under environmental conditions presents problems seldom experienced in avionics.
Many electronic subsystems are present in an automobile and the number increases each year. Among these are:
Electronic engine controls (EEC).
Anti-lock braking systems (ABS).
Heating, ventilating and air conditioning (HVAC) or climate control.
Air-bag actuation systems.
Audio subsystems.
Ride control.
Transmission control.
Navigation and communications.
While each of these subsystems presents some interesting requirements for testing, we limit this discussion to EEC, ABS, HVAC and air bags.
Technical Issues
Automotive subsystems perform their functions in an electromechanical environment characterized by very high energy and energy conversion levels. As a result, the signal levels and loadings differ vastly from those seen in typical electronic product testing. Generating or measuring spark-plug, brake solenoid, air-bag squib, motor control or similar signals requires combinations of voltage and current levels outside the normal measurement range of typical ATE.
To make matters worse, these signals are often to and from highly inductive or highly capacitive loads that are not kind to typical instruments. Many of the reference-signal inputs to these subsystems also are phase continuous and vary in frequency with time. Arbitrary waveform generators or synthesizers that easily generate such signals over somewhat limited ranges can mean high costs for multiple instruments that end up functioning over a very limited portion of their available ranges.
The need to reduce automobile wiring costs and requirements for service diagnostic tools have driven the industry to use automotive standard data buses. These vary from the CAN bus (Europe), Chrysler Collision Detection, Ford’s HBCC and the newer SAE/J1850 (with multiple protocols) to versions of the MIL-STD-1553 avionics bus on some trucks. Each requires special consideration in the test-system design.
Environmental requirements come into play with ABS and air-bag actuator subsystems. ABS require 100% testing during thermal cycling that takes several hours. The air-bag actuator not only may require thermal testing but also testing under actual shock conditions. Both of these requirements dictate the need to test many products simultaneously to meet production rates.
Table 1 shows the requirements placed on a tester by various automotive electronic subsystems. Common to all of these subsystems is the need to provide variable battery input voltages, often with significant current levels, sensor simulation as variable resistive or voltage inputs, and inductive or capacitive loads.
Solutions
Depending on the product and the volume requirements, it is common to see multiple levels of test on a subsystem production line. Standard in-circuit test/manufacturing defect analyzers can still be valuable as a first test step, and conventional functional test may be found on some lines. But once the product becomes an operational subsystem, the functional tester, be it VXI or rack-and-stack, must be augmented to accommodate the product’s unique signals.
This accommodation may take place in several forms. These include ATE vendor-specific personality boards, load and personality panels specific to the customer’s product, and industry-standard daughter cards for custom requirements.
At least one vendor has developed families of card extenders that create custom switching, loads and signal-generation circuitry to more easily adapt its standard VXI offering to automotive test. This significantly reduces the cost of creating a tester to meet a specific product’s requirements.
When the number of testers is sufficient, some vendors provide a mounting panel on a side cabinet door to affix loads, custom signal sources, measurement circuits, switching and communications circuits so as to be easily maintainable and readily integrated with standard ATE hardware and software environments.
C&H also is developing a family of IndustryPack and M Module (industry standards) daughter cards for automotive bus communications interfaces, wheel-signal generation and other loading and measurement functions. These modules will be used with the company’s VXI IP and M Module carriers to bring more of the functions required back into the VXI rack in a modular and cost-effective manner.
The need for testing tens to hundreds of products during environmental conditioning requires the nearly simultaneous testing of all products. Frequent test cycles and long wiring distances seldom make it practical to use more conventional ATE approaches.
More often than not, some form of tester-per-product architecture is developed to meet specific requirements. These testers—often called load cells from the time when the need to acquire product specific data was not as pressing—generally are processor based to provide an interface between the product and a data collection computer. All loading, signal generation and measurement usually are provided by such a load cell.
Summary
The rapidly growing automotive electronics market has been creating great challenges for the ATE community. As a result, we see modular approaches evolving to make it easier and more cost-effective to integrate both VXI and other forms of automotive test equipment in the future.
About the Authors
Fred Harrison, Ph.D. is the president and CEO at C&H Technologies, and has more than 20 years experience in ATE. Dr. Harrison earned B.S. and master’s degrees from the University of Maine and a doctorate in electrical engineering from Lamar University.
Bennie Kirk is a member of the technical staff at C&H Technologies. He graduated from the University of Texas with a B.S. degree in electrical engineering.
Gary Guilbeaux is the director of design engineering at C&H. He received a B.S. degree in electrical engineering from the University of Texas.
C&H Technologies, P.O. Box 14765, Austin, TX 78761, (512) 251-1171.
Copyright 1997 Nelson Publishing Inc.
May 1997