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SCAT (Sneak Circuit Analysis Tool)

Can You Afford Not to Do Sneak Circuit Analysis?

Imagine..

  • One brake in an automobile suddenly engages because of an unexpected current flow caused when a turn signal relay disconnects
  • The detonation circuitry in a cruise missile is triggered prematurely because it shares a ground plane with a high current servo control circuit

SCAT the  automated tool for Sneak Circuit Analysis will detect design flaws that can lead to such scenarios by finding all:

  • Reverse current flows (H-patterns)
  • Power source to power source current flows (Y-domes)
  • Ground-to-ground current flows
  • Momentary undesired current paths during switching

For more information, please review our brochure.

What is Sneak Circuit Analysis (SCA)?


Sneak Circuit Analysis is performed on systems that include irreversible functions (e.g., rocket engine firings, squib ignitions, or release mechanisms). The objective of SCA is to ensure that there is no possible system configuration that could induce accidental actuation of such devices.

A sneak circuit exists when under some, usually very rare and unexpected, conditions an output is furnished when not desired, or an output is inhibited when desired. The worst consequences of sneak circuits have been in electro-explosive devices (squibs), and Sneak Circuit Analysis (SCA) has been mandated in many military applications where squibs are used. MIL-STD-1543 requires SCA for most spacecraft, launch vehicle, and missile systems. Although the standard is inactive, the provisions regarding SCA incorporated in the practices of many space and missile agencies. SCA has also become increasingly important for the automotive industry as electrical and electronic devices with complex logic paths are used to control engine, brake, and other vital functions in cars.

The cause of sneak circuits is unexpected and unintended direction of current flow in a branching electrical network. When a load is controlled by a switch from a single source and is connected to a single return (ground) there is no possibility of a sneak circuit. Current will always flow from the source to the return. But as soon as even a single branch is added, current may flow in the direction opposite to that which is intended. The undesired and unintended events occur only under rare conditions or when established procedures are not followed. The objective of SCA is specifically the prevention of these rare but high consequence events. SCA is therefore an appropriate technique for the investigation of the infrequent and unexplained occurrences.

In the simple example shown in the figure, the circuit is designed to drop lower the landing gear and open the cargo door when a normal landing takes place and to open the emergency door but keep the landing gear up in an emergency landing. The red path shows a sneak circuit whereby the closing of both switches will cause the emergency door top open and the landing gear to be lowered simultaneously, an action that could result in a disaster.

A complete SCA will identify, check and verify every possible current path in a complex system

  • Larger systems can have millions of potential current flows
  • Most analysis is done manually today using valuable design engineering time or costly consultants

Tool Overview

What is SCAT?

SCAT (Sneak Circuit Analysis Tool) is a Windows program used for automatically identifying potential sneak paths (i.e., paths which inhibit desired functions or cause undesired outputs) by processing circuit schematics.

SCAT has a modern easy to use GUI that automates both the preparatory work and the actual analysis that are part of SCA. When user input is required (such as identifying ports) the GUI clearly prompts and offers automated menus that induce a streamlined and smooth work experience.

The SCAT Approach to Sneak Circuit Analysis

SCAT differs from conventional SCA (Sneak Circuit Analysis) techniques in that the latter are based upon the generation (usually automated) and analysis (mostly manual) of network trees to identify sneak paths. In contrast, SCAT does not require or even make use of the traditional network trees.

The automated procedure provides the design engineer or reliability analyst with a simple yet powerful tool for rapidly identifying and correcting sneak paths. The automated procedure is based on the fact that sneak paths involve circuit components which can conduct current in either direction depending upon the switching state of the circuit. SCAT exhaustively searches for these bidirectional branches which is more readily automated than searching for specific topological circuit patterns, as done by conventional SCA techniques. Furthermore, the analyst's task is reduced to evaluating the significance of specific potential sneak paths rather than applying "clue lists" to circuit patterns for identifying the sneak paths.

A significant issue that arises is the assurance that sneak paths associated with interconnecting assemblies or subsystem interfaces are not overlooked. This issue is addressed in two ways. First, the system compels the user to identify each interface port of a switching circuit in terms of it being a power input. Interfaces to power and ground are labeled as such regardless of whether they respectively go to power and ground directly or through switched or un-switched loads, and they are included within the sneak path search.

SCAT was developed to enable design engineers to perform SCA early in the project life so that problems can be corrected early and at minimal cost.

Performing a Sneak Circuit Analysis with SCAT
There are three steps in using SCAT: preparation, analysis and evaluation. These tasks have been automated utilizing a concurrent engineering environment comprising the EDIF 2.0 netlist file format for schematic capture and the SCAT software.
Preparation
Preparation consists of automated pre-processing of the schematics, netlist generation, netlist processing, power port selection and optional switch and capacitor modeling.

 

Analysis
SCAT can perform sneak circuit analysis with a single command. A printable session log (audit trail) describing all actions taken by the user during the analysis is stored and can be printed out as analysis documentation. The user can easily change the input parameters to SCAT and rerun previous analyses. The first step is performing a sneak circuit analysis which identifies all the source to sink paths and among them finds all the bi-directional paths. The next analysis is the power-to-power analysis which finds all the source-to-source and all the sink-to-sink paths which are, by definition, bi-directional paths.

SCAT TOOL ACTIVATION

Evaluation
Evaluation consists of viewing the asterisked bi-directional paths on the listing and all the power-to-power (source-to-source and sink-to-sink) paths. Where such a path is encountered the analyst must decide whether it is

  1. An intended bi-directional current path
  2. An unintended bi-directional path through a high resistor that limits the current to a fraction of the actuation load - or
  3. A true sneak circuit that must be eliminated.

    SCAT SNEAK ANALYSIS PATHS LIST

    SCAT POWER-TO-POWER PATHS LIST


Functional Packages:
PREDICTOR

  • 5 Standard Operating Reliability Prediction Methods
  • BOM Builder, Temperature Curves, Mission Profile, and Import Wizard
  • Full set of ready-to-print Reliability Reports
  • Enhanced Report Generator for user defined reports

RELIABILITY PRO

  • 5 Standard Operating Reliability Prediction Methods
  • BOM Builder, Temperature Curves, Mission Profile, and  Import Wizard
  • User Defined Components Reliability Data Module
  • Full set of ready-to-print Reliability Reports
  • Enhanced Report Generator for user defined reports
  • Components Library Module (over 400k components)
  • RBD - Reliability Block Diagram

MAINTAINABILITY PRO

  • Maintainability Module (according to MIL-STD-472 Procedure 5A)
  • Built in libraries for Tasks, Times, STE, Skills, and Materials
  • Maintenance Engineering Report (MEA Report)
  • Maintenance Task Analysis Report
  • Full set of ready-to-print Reliability Reports
  • ILS Supprt Fields (user defined)
  • BOM Builder, Temperature Curves, Mission Profile & Import Wizard
  • Enhanced Report Generator for user defined reports
  • RCM/MSG-3 Module
  • FMECA Module

FAILURE ANALYSIS & ISOLATION

  • BOM Builder, and Import Wizard
  • FMECA (covering both Hardware & Functional) Module
  • Customizable FMECA Worksheet
  • FTA Module
  • FMECA Import/Export
  • Testability Module
  • Full set of FMECA & FTA ready-to-print Reports
  • Full set of ready-to-print Testability Reports including graphical trouble shooting, fault isolation, etc.
  • FMD-97 Library
  • Enhanced Report Generator for user defined reports

SAFETY ASSESSMENT

  • SSA supporting IEC 61508 (Safety Standard for Safety Instrumented Systems) and MIL-STD-882D (SHA, O&SHA), SAE, ARP 4754A, and ARP4761
  • Customizable FMECA Worksheet
  • FTA Module
  • RBD Module
  • Markov Chains Module
  • FMECA Import/Export
  • Full set of ready-to-print Safety Reports
  • Enhanced Report Generator for user defined reports

AVIATION SAFETY

  • SSA & FHA according to SAE, ARP 4754A, ARP4761, and FAR 25 1309b
  • FTA including ready-to print reports
  • MSG-3 (System, Zonal, and Structural) including ready-to-print reports
  • MMEL including ready-to-print 5-column report
  • FMECA including ready-to-print FMECA reports, BOM Builder, and Import Wizard
  • Enhanced Report Generator for user defined reports
  • Report Template Utility for layout customization



 



 

 
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Reliass Reliabilty Safety Software: Managing Reliability Across All Product Lifecycle