Low-level Fault Research Articles

Design of a Self-Checking Microprocessor for Real-Time Applications

This paper deals with the design of a microprocessor dedicated to safety applications and more particularly to Automatic Train Control. This microprocessor is self-checking i.e. able to detect its own errors. Its name is COBRA for Controller with Built in self-checking for RealTime Applications.In the design of this circuit, low-level fault hypotheses for the N-MOS technology are considered. In this case redundant faults, i.e. undetectable faults, generally exist in any design and thus fault detecting capabilities must be provided for sequences of faults. The functional circuits will process with coded data and will be checked by Strongly Code Disjoint Checkers.COBRA is a microprocessor-type device, its data path processes independently 19 different signals: date out external events, measure frequencies, and supervise 14 level inputs (binary values). 7 independent outputs could be binary values, or clocks, for 3 of them. The data path communicates with an external PROM, used as program storage for COBRA. This PROM is addressed with 14 bits, multiplexed over the 8-bit address/data internal bus of the data path. It contains also one serial I/0, a 64 byte RAM, and 3 independent 14 bits counters. An 8 bit ALU could be used for arithmetical or logical operations. A set of 42 instructions processes all these operations.

Design of a Self-Checking Microprocessor for Real-Time Applications

This paper reals with the design of a microprocessor dedicated to safety applications and more particularly to Automatic Train Control. This microprocessor Is self-checking i.e. able to detect its own errors. Its name is COBRA for Controller with Built in self-checking for Real-time Applications.In the design of this circuit, low-level fault hypotheses for the N-MOS technology are considered. In this case redundant faults, i.e. undetectable faults, generally exist in any design and thus fault detecting capabilities must be provided for sequences of faults. The functional circuits will be Strongly Fault Secure [SMI 78] and the checkers will be Strongly Code Disjoint [NIC 84-2].COBRA is a micropressor-type device, its data path processes independently 19 different signals : date out external events, measure frequencies, 8nd supervise 14 level inputs (binary values). 7 independent outputs could be binary values, or clocks, for 3 of them. The data path communicates with an external PROM, used as program storage for COBRA. This PROM is addressed with 14 bits, multiplexed over the 8-bit address/data internal bus of the data path. It contains also one serial I/O, a 64 byte RAM, and 3 independent 14 bits counters. An 8 bit ALU could be used for arithmetical or logical operations. A set of 42 instructions processes all these operations.

Fault localisation when testing complex circuits

An approach to state functional diagnoses when testing complex integrated circuits is presented. Such an approach can lead in some cases to low-level fault localisation. Experiments using the capabilities of a realised test system (GAPT test program generator, specific tester), illustrating the efficiency of this approach, are presented.

A Better Approach to Motor Circuit Protection

Over the years, various approaches including both thermal magnetic breakers and several types of fusible devices have been used in motor circuit protection schemes with acceptable results. Evidence reported in the trade magazines indicated that the level of protection from these types of devices was not totally effective. For the first time, with the printing of the 1968 National Electric Code, the application of instantaneous trip circuit breakers (without time delay) was allowed provided the pickup could be adjusted above 700 percent to a maximum of 1300 percent of the motor full-load ampere rating. After extensive testing the first product complying with these requirements was introduced to the market in 1969. Experience in motor failures indicates that most faults occur at relatively low levels of fault current just above lock rotor values rather than at higher levels. With rapid clearing of faults in the low-level range such as can be accomplished with the use of instantaneous trip circuit breakers, extensive damage to motors as well as to control equipment can be greatly reduced. By combining low-level protection obtained with the high interrupting capabilities of specially designed current limiters, a full range of coordinated protection is available for both high-and low-level faults.