A fault model is an engineering model of something that could go wrong in the construction or operation of a piece of equipment. From the model, the designer or user can then predict the consequences of this particular fault. Fault models can be used in almost all branches of engineering.

Basic fault models in digital circuit

Digital circuit

Digital electronics represent signals by discrete bands of analog levels, rather than by a continuous range. All levels within a band represent the same signal state...

s include:

• the stuck-at fault
  Stuck-at fault
  A stuck-at fault is a particular fault model used by fault simulators and automatic test pattern generation tools to mimic a manufacturing defect within an integrated circuit. Individual signals and pins are assumed to be stuck at Logical '1', '0' and 'X'...
  
   model. A signal, or gate output, is stuck at a 0 or 1 value, independent of the inputs to the circuit.
• the bridging fault
  Bridging fault
  A bridging fault consists of two signals that are connected when they should not be. Depending on the logic circuitry employed, this may result in a wired-OR or wired-AND logic function...
  
   model. Two signals are connected together when they should not be. Depending on the logic circuitry employed, this may result in a wired-OR or wired-AND logic function. Since there are O(n^2) potential bridging faults, they are normally restricted to signals that are physically adjacent in the design.
• The open fault model. Here a wire is assumed broken, and one or more inputs are disconnected from the output that should drive them. As with bridging faults, the resulting behavior depends on the circuit implementation.
• The delay fault model, where the signal eventually assumes the correct value, but more slowly (or rarely, more quickly) than normal.

A fault model in an Aerospace context is a set of structured information which helps users or systems to identify and isolate a problem that occurs on an engine, Line-replaceable unit

Line-replaceable unit

A line-replaceable unit is a modular component of an airplane, ship or spacecraft that is designed to be replaced quickly at an operating location. An LRU is usually a sealed unit such as a radio or other auxiliary equipment...

 (LRU), or Auxiliary power unit

Auxiliary power unit

An auxiliary power unit is a device on a vehicle that provides energy for functions other than propulsion. They are commonly found on large aircraft, as well as some large land vehicles.-Function:...

 (APU) during a flight. Associated with this fault model may be a suggested repair procedure along with references to Aircraft maintenance manuals (~ Light maintenance manual ).

See also

• Automatic test pattern generation
  Automatic test pattern generation
  ATPG is an electronic design automation method/technology used to find an input sequence that, when applied to a digital circuit, enables automatic test equipment to distinguish between the correct circuit behavior and the faulty circuit...
  
  
• Single Stuck Line
  Single Stuck Line
  Single stuck line is a fault model used in digital circuits. It is used for post manufacturing testing, not design testing. The model assumes one line or node in the digital circuit is stuck at logic high or logic low...
  
  
• Fault coverage
  Fault coverage
  Fault coverage refers to the percentage of some type of fault that can be detected during the test of any engineered system. High fault coverage is particularly valuable during manufacturing test, and techniques such as Design For Test and automatic test pattern generation are used to increase...