Programmable controller system with failure indicator

摘要

A programmable controller system is taught which uses an oscillator to provide a relatively low frequency low duty cycle series of digital ones and zeros to the gate logic of a load control device regardless of whether the device is in the ON or OFF state. These signals are electrically passed through the system which controls the load for such a short time that the load cannot change state because of electrical momentum and/or inertia thereof. The series of digital ones and zeros nevertheless do pass through the system and sensing means serve to test the correct operation of the output devices. As long as the oscillator generated signals continue to pass through the gate, the capacitor controlled sensing devices will be held in a state such as to provide no indication of failure. The only time a failure indication will take place is if the latter signals do not make it through the array of electronic devices in which case the discharge or charging characteristics of the capacitor controlled sensing circuitry would eventually cause an indication of failure even though the load may remain unaffected. The system as taught gives an indication of failure when the next load state change is unlikely to occur because command signals therefore will not pass through the logic system.