Ventura Aerospace was presented with a unique challenge from a customer. Their current Solid State Relay (SSR) solution for opening and closing a valve was experiencing start up failures. The typical failure mode of an SSR is to fail to the closed position. The problem was that if the SSR failed at start up the connected valve would open out of sequence resulting in possible test article damage.

The solution was to design a dual SSR circuit that was triggered from a single digital line that would provide fail safe coverage. To accomplish this, one SSR is used for power while the other is used for ground. Both SSRs are triggered by the same digital input. If one SSR fails to open position on power up the connected valve will not operate as the circuit path is not completed. Individual LEDs are provided for each SSR which allows for a quick visual diagnostic. An optically isolated diagnostic circuit provides a TTL level trigger for each channel that can be monitored in the LabVIEW executable to determine whether a failed SSR is present and provide a closed loop feedback if desired. This diagnostic circuit is triggered from the high-power output of the SSRs which provides the most reliable method for detecting a SSR failure.

This board is tested using a National Instruments cDAQ and a custom bench mounted load circuit that stresses each SSR pair to 100% of load capacity. This automated test reduces the Quality Assurance overhead required to complete the part while providing a better solution to our customer.

For information on this product or any of the other solutions that Ventura Aerospace offers please contact us.