High availability solenoid system
Houston, Tex. -Expanding on the popular 2oo2 (two out of two) voting design, ASCO (Florham Park, N.J.) and SIS-Tech Solutions (Houston, Tex.) have co-developed the 2oo2D-SOV, an integrated solenoid solution for safety protection systems requiring a high level of availability and reliability.
Suitable for use in areas with Class I, Division II, Groups A, B, C, and D classification, the 2oo2D-SOV (patent pending) combines a keyed bypass switch, two pressure switches, and two solenoids to form a system that provides on-line diagnostics of solenoid status and facilitates on-line testing. When activated, a keyed switch bypasses the pressure switch/solenoid pneumatic circuit and maintains air pressure on the valve actuator, permitting online tests to be conducted without compromising protection integrity or concern for nuisance trips. The pneumatic circuit ensures system integrity by using the pressure switches to verify one solenoid is energized before de-energizing the other solenoid. During normal operation, the pneumatic signal passes through the 2oo2D-SOV from the signal source to the control or block valve actuator. When a trip occurs, air is vented from the process valve actuator, allowing the actuators spring to move the process valve to its fail-safe position.
Connecting the 2oo2D-SOV to a controller requires two digital outputs, one for each solenoid; and three digital inputs, one for each pressure switch and one to indicate bypass switch position. Applications requiring high availability and reliability and/or those protected by safety instrumented systems can improve their overall protection integrity by including the 2oo2D-SOV as part of the protection system design.