Computer control hardware faults

The hardware and software used to implement LIMS systems must be vahdated. Computers and networks need to be examined for potential impact of component failure on LIMS data. Security concerns regarding control of access to LIMS information must be addressed. Software, operating systems, and database management systems used in the implementation of LIMS systems must be vahdated to protect against data cormption and loss. Mechanisms for fault-tolerant operation and LIMS data backup and restoration should be documented and tested. One approach to vahdation of LIMS hardware and software is to choose vendors whose products are precertified however, the ultimate responsibihty for vahdation remains with the user. Vahdating the LIMS system s operation involves a substantial amount of work, and an adequate vahdation infrastmcture is a prerequisite for the constmction of a dependable and flexible LIMS system. 

A traditional approach to fault diagnosis in the wider application context is based on hardware i.e. physical) redundancy methods which use multiple lines of sensors, actuators, computers and software to measure and/or control a particular variable. Typically, a voting scheme is applied to the hardware redundant system to decide if and when a fault has occurred and its likely location amongst redundant system components. The use of multiple redundancy in this way is common, for example with digital fly-by-wire flight control... 

For the water analysis, automation is clearly best achieved with an auto-injector for the mechanical handhng of the samples coupled with on-hne data capture, using the computer to analyse the peak data. Serious consideration was given to employing the very considerable in house automation experience to construct a purpose-built auto-injector. However, in the interests of a speedy implementation of the automatic system, it was decided to purchase a commercially available auto-injector and to concentrate the laboratory s efforts on the area of on-hne data capture. Interfacing the complete system assembly via a data communications network required the development of a special control device (commhox), which allowed the LGC hardware to run unattended hut provided an audible warning in event of a fault condition. 

The fault tolerant design discussed here mainly pertains to computing systems and intelligent systems for real-time computer systems such as DCS/PLC and/or associated intelligent devices. Here, the discussion is on the basics of hardware and software fault tolerant principles in computing systems, whereas that applicable to control systems is covered in Clause 1.2. Two ways in which fault tolerant designs can be developed are hardware technique and software technique. 

Various types of ship-control systems are used in submarines. The ship-control system used in the Seawolf submarine represents the state of the art for such sysfems. This sysfem incorporates various features, including a fault-tolerant computer, automatic modes of control for steering, and flat-panel operator displays [23]. High-speed data buses permit the ship control to interface effectively with the data distrihution system, gyrocompass inertial sensors, and the combat system. Furthermore, hardware redundancy and performance-monitoring software permit the system to function after experiencing malfunctions of ship sensors, control electronics, and the actuation systems it controls. 

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