Sunday, January 8, 2012

Computers in Automated Test Equipment

Computers in Automated Test Equipment (ATE) A computer system can serve as a useful tool for identifying and managing problems that may arise in electronic equipment. Through the use of add-on interface cards and specialized software, a wide variety of testing methods can be applied and numerous instruments can be attached to a computer in order to perform automated testing. Functional and in-circuit are the two most common types of standalone automated testing instruments. Functional testing assesses a device to determine its faults and is an effective method for evaluating printed circuit boards and subassemblies. It provides relatively rapid qualification checks and is accurate in detecting dynamic faults. Functional testing can successfully perform high-volume testing on printed subassemblies, but may require advanced knowledge of a device in order to set appropriate test patterns and programming.

By contrast, in-circuit testing is more of a diagnostic operation used to verify the quality of individual components in a subassembly. It operates by evaluating each component and detecting any failed parts or flaws. While this method offers detailed testing results, it may not always perform at the clock rate of the subassembly being tested and certain abnormalities, such as race conditions and propagation delays, may go unidentified. Both functional and in-circuit automated testing equipment can provide useful information in component quality-control processes and for evaluating performance parameters for test devices. When coordinated with computer systems, these testing methods can have their efficiency further improved.

Accessing Printed Circuit Boards

There are two major ways for automated test equipment to gain access to vital points on a printed circuit board. In the bed of nails method, a subassembly is mounted onto a dedicated testing apparatus using a vacuum or mechanical attachment process. Individual components on the board are examined with probes sent through essential electrical traces. Through a back-driving technique, input from each component is isolated from related circuitry and the component functions are tested. The process is quick but can be relatively expensive, making it better-suited for high-volume subassembly testing and maintenance.

An alternative method involves the use of printed circuit board clips in place of a dedicated testing apparatus. In this process, an operator mounts a series of clips onto specific locations on the board in order to check device functionality. Normally, it is not necessary to maintain simultaneous access to all components on the board, so the testing system relies on less intensive hardware and programming requirements. Some clip systems also include software packages that enable them to test multiple classes of equipment. Testing time for a standard printed circuit board clip may take up to twenty minutes, which is significantly slower than the operation rate for the bed of nails method, and the clip technique is usually more effective in low-volume applications.

Computer Interface Systems

In automated testing, there are several types of interface systems that can be used to connect computers to testing instruments. The general purpose interface bus (GPIB) and the standard serial interface (RS-232) are common nonproprietary interfacing systems that share numerous characteristics while also providing their own distinct benefits. GPIB and RS-232 can both connect multiple measuring instruments to a computer and both are bidirectional, allowing computers to send and receive data from external components. However, the GPIB interface is more frequently used among test instruments, with thousands of different instruments relying on this format.

RS-232 interfaces, by contrast, are more commonly found in computer applications, as well as printers, scanners, and modems. Remote sensing instruments, such as thermometers and frequency signal strength meters, are the most common types of testing instruments that use RS-232 interfaces instead of the GPIB alternative. Each interface format works differently depending on the application. RS-232 is often found already installed in personal computers, making it a popular choice for automation systems, while GPIB is more often seen in test equipment.

Automated Testing Software

Automated testing systems are often equipped with software packages that enable customization of instrument performance to meet application parameters. An operator inputs a series of codes for each instrument required for the testing process, sets the types of measurements that need to be taken, and determines how the testing results will be stored. After the configuration settings have been established, the software program compiles the processing codes for each instrument in order to initiate performance. This level of automatic programming minimizes the need for programming expertise on the part of the operator, and typically offers a simple set of graphic symbols for the user to manipulate.

Computer-Automated Testing Applications

Typical applications for computer-controlled automated test equipment include product qualification, data gathering, and troubleshooting, all of which rely on software that automatically controls the instruments. Data acquisition can sometimes be accomplished using only a computer and a single instrument. A computer can be designated to take numerous readings until a specific event occurs, such as a rise or drop in voltage that exceeds a preset limit or the elapsing of a preset time limit for the test. The computer then stores the readings from various testing points on the device. An automated system can also set its instruments to perform tasks that would be impractical or impossible to conduct manually while controlling the power supplies, generators, and frequency counters that may be included in the testing equipment.

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