Downloaded from https://www.everyspec.com ADS-79D-HDBK loop, so the loop is said to be ―open.‖ Examples of open loop tests include lamp and gauge tests, switch tests, and other tests that usually involve operator controls and displays There are generally two kind of testing environments, in-situ or depot environment. There resources available for each environment would greatly effects the diagnosis. H.3.3.3 Testing in In-Situ Environments In situ tests are executed at the O-level, with the UUT installed in its normal operating environment. In situ test are often referred to as Built-in Tests (BITs) and can also be categorized by their execution time relative to system state.
In situ test and BITs can be conducted offline or online. Offline tests are executed outside of normal system operation, often in a specialized test environment. Online tests are a collection of background diagnostics that can run in parallel with normal system operation without affecting it. Offline and online in situ test and BITs are described in more detail in the following sections. H.3.3.3.1 In situ offline Tests In situ offline tests are characterized by when and how they are executed. Typically, a collection of tests is run when the system is powered-on and initiated, with additional tests being run on request.
These tests are executed when the prime function of the system is non-operational, or ―offline.‖ The power-on and initiation tests directly support the Verification of Operational Readiness diagnostic, while operator-initiated tests more directly support the Fault Isolation, Repair of Repairable, and Other Maintenance Action diagnostic. Offline in-situ tests can include power-on BITs, power-on self-tests, and initiated BITs, which are described in more detail in the next section. H.3.3.3.1.1 Type of BIT: Power-on BITs, often referred to as PBIT (power-on BIT) or IBIT (initial BIT) tests, are tests that run automatically when a system is powered-up and initialized.
They are typically closed loop and support the Verification of Operational Readiness mission. PBIT tests can have an additional sub-category of tests called power-on self tests (POSTs). POSTs are a subset of PBITs. POSTs are a set of low-level tests, usually developed by a commercial off-the-shelf (COTS) hardware vendor or specialized hardware developer. They are hosting in non-volatile memory and execute prior to system software boot. One of the jobs of PBIT is to collect the diagnostic information from the various POST tests. Initiated BITs, (IBITs) also referred to CBITs (commanded BITs) are tests that run when an operator initiates them.
IBITs support the Fault Isolation and Diagnosis and Repair of Repairable missions. Initiated BITs usually consist of a subset of PBIT tests augmented with additional diagnostics. The additional diagnostics can include open loop tests to verify controls and displays and tests to verify proper communication and interaction with other connected systems. Initiated BIT tests can run as a single iteration or as a repeating set of one or more tests. Repetitive execution of the tests is necessary to help detect and isolate intermittent failures. H.3.3.3.1.2 Online Tests In situ online tests are run periodically or continuously in the background during normal system operation.
Continuous BITs or periodic BITs are online tests that run in the background to support the Fault Detection and Characterization diagnostic mission. They are typically either closed loop tests or statistics collection activities that attempt to verify that data is flowing properly across the entire system. Examples of continuous BIT tests include the collection of network interface error statistics (such as checksum failures or parity errors) and other closed loop tests that can be run without affecting normal system operation. 140