Failsafe AC Hi-Lo Limit Detector

A very accurate alternating current limit detector is presented. Its design philosophy, specially suited for multi-channel applications is based on dynamic monitoring of both limits through the same channel. Completely solid-state, this limit detector exhibits an accuracy of ± 0.1 % over a temperature range from 0 to 45° C. The design is inherently failsafe; and reliability evaluations were performed for a 1000 channel application. Design philosophy, circuit diagrams and system operation are presented in detail and discussed.