One such improvement in system testing is the design of a method that can test systems at various
functional levels. This allows groups of components to be tested as a whole and reduces the time required
to test components individually. One advantage of this method is that complete test plans can be written
to provide the best sequencing of tests for wave shape or voltage outputs for each functional level. This
method of testing has led to the development of special test sets, called AUTOMATED TEST
EQUIPMENT (ATE). These test sets are capable of simulating actual operating conditions of the system
being tested. Appropriate signal voltages are applied by the test set to the various functional levels of the
system, and the output of each level is monitored. Testing sequences are prewritten and steps may be
switched-in manually or automatically. The limits for each functional level are preprogrammed to give
either a "go/no-go" indication or diagnose a fault to a component. A go/no-go indication means that a
functional level either meets the test specifications (go) or fails to meet the specifications (no-go).
If a no-go indication is observed for a given function, the area of the system in which it occurs is
then further tested. You can test the trouble area by using general purpose electronic test equipment and
the troubleshooting manual for the system. General purpose electronic test equipment (GPETE) will be
discussed later in this topic. (Effective fault isolation at this point depends on the experience of the
technician and the quality of the troubleshooting manual.) After the fault is located, the defective part is
then replaced or repaired, depending on the nature of the defect. At this stage, the defective part is usually
a circuit card, a module, or a discrete part, such as a switch, relay, transistor, or resistor.
BUILT-IN TEST EQUIPMENT
One type of fault isolation that can be either on-line or off-line is BUILT-IN TEST EQUIPMENT
(BITE). BITE is any device that is permanently mounted in the prime equipment (system); it is used only
for testing the equipment or system in which it is installed either independently or in association with
external test equipment. The specific types of BITE are too varied to discuss here, but may be as simple
as a set of meters and switches or as complex as a computer-controlled diagnostic system.
ON-LINE TEST EQUIPMENT
Functional-level testing and modular design have been successfully applied to most electronic
systems in use today; however, the trend toward increasing the number of subassemblies within a module
by incorporating microelectronics will make this method of testing less and less effective.
The increased circuit density and packaging possible with microelectronic components makes
troubleshooting and fault location difficult or, in some cases, impossible. The technician's efforts must be
aided if timely repairs to microelectronic systems are to be achieved. These repairs are particularly
significant when considered in the light of the very stringent availability requirements for today's systems.
This dilemma has led to the present trend of developing both ON-LINE and OFF-LINE automatic test
systems. The on-line systems are designed to continuously monitor performance and to automatically
isolate faults to removable assemblies. Off-line systems automatically check removable assemblies and
isolate faults to the component level.
Two on-line systems, the TEST EVALUATION AND MONITORING SYSTEM (TEAMS) and the
CENTRALIZED AUTOMATIC TEST SYSTEM (CATS), are presently in production or under
development by the Navy.
Test Evaluation and Monitoring System (TEAMS)
TEAMS is an on-line system that continuously monitors the performance of electronic systems and
isolates faults to a removable assembly. This system is controlled by a computer using a test program on
perforated or magnetic tape, cassettes, or disks. Displays are used to present the status of the equipment
and to provide data with instructions for fault localization. Lights, usually an LED, are used to indicate