I/O libraries that typically ship with LXI devices provide one user interface to access all standard PC interfaces such as Ethernet/LAN, USB, or RS-232, as well as test-and-measurement interfaces like LXI, GPIB, or VXI. These libraries provide interface debugging tools and the flexibility to use either drivers or native instrument commands for controlling each instrument.
FIXTURE INTERFACE
When specifying components for a core system, the fixture interfaces are critical. Fixture interfaces should be specified for more than 20,000 fixture changes without maintenance.
OPEN SYSTEM SOFTWARE
Often more than 50% of the cost of implementing a test system is related to software engineering. One key to reducing software development costs is to use commercially available test sequencers coupled with a modular software approach that maximizes code reuse. A successful software strategy includes:
- Choosing programming languages and instruments designed to be “open.”
- Using commercial “off-the-shelf” applications for the intended software environment.
- Using defined software layers APIs to provide docking points for customized functions.
- Reusing instrument code via test step libraries.
- Fast test-sequence execution that meets real-world requirements, including comprehensive user interfaces, reporting functionality, and integration into automated-manufacturing environments.
TEST EXECUTIVE
The test executive includes a runtime engine that interprets and executes test sequences, evaluates test results against the limits defined in the test sequence, and provides APIs for control by the operator interface at runtime. The API also supplies status information to the operator interface, as well as a test sequence development environment.
TEST SEQUENCES
Test sequences define the individual tests used to evaluate a DUT and include test parameters, limits, and the order of execution of test steps. The integrated test-sequence development environment allows test engineers to focus on defining test-sequence content and test methodologies rather than developing instrument-control code, data handling, and other low-level programming tasks.
SWITCH MANAGEMENT
In a micro-PLC system, switch handlers control complex topologies that are defined by a switching topology editor. The user defines the switch route to be used for a given test. At runtime, the software closes all relays on the switch path prior to execution of the test and opens them after execution of the test. OTP-based systems are delivered with switch control software and predefined switch topologies to make it easier to develop test sequences.
INSTRUMENT DRIVERS
Instrument drivers encapsulate instrument complexity and provide programmatic access to the instruments without having to learn the underlying SCPI syntax.
DATA REPORTING AND ARCHIVING
The OTP software architecture separates data reporting and archiving from the individual test sequences and utilizes the APIs provided by the test sequencer. The test executive takes care of collecting data, displaying results, and storing them. The OTP approach enforces consistent data handling for all sequences and helps standardize test data formats throughout the test floor.
OPERATING SYSTEM AND INTERFACE LIBRARY
The OTP software foundation is built on Microsoft Windows. All instruments are programmed using the VISA interface driver framework, which also supports interfaces such as FireWire (VXI), USB, RS-232, and GPIB (IEEE 488.2). The standard system core can be extended to provide test capability for a variety of other industries and applications. This core could work with other applications as well:
- RF and microwave measurements and switching (aerospace/defense, telecommunications, automotive)
- Serial communication interfaces (industrial automation, automotive)
- Higher voltages and currents (white goods, automotive, and industrial automation industries)
- Optical inspection and mechanical stimulus (applications in all industries)
This system used a multifunction switch/measure unit and open software standards to create a standardized open test platform that made it easier to develop and support custom functional test systems. Whether developing a test system in house or using a system integrator, the basic principles outlined here can be used to create a test system that meets a range of needs.
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