Reliable Partial Stroke Test Independent from Valve Status

A partial stroke test is used for testing safety valve functions. According to IEC 61508 and IEC 61511, this procedure is essential in safety applications in order to ensure availability and detect failures. Partial stroke tests:

• Reduce the probability of failure in safety functions
• Reveal malfunctions
• Keep the PFD (probability of dangerous failure on demand) low

Conventional valves in safety applications typically contain two components: a binary input for emergency shutdown according to SIL 3, and an additional positioner for 4…20 mA / HART operation. The partial stroke test is either initiated in active mode via HART communication or by using a second signal connection between the control system and valve.

In case intelligent field devices are used, solutions with the KFD2-RCI-Ex1 are the right choice. The solenoid driver communicates with the field device using one connection. It offers complete diagnostic information even when the valve status is OFF. For this solution, only the single channel isolated barrier is necessary. The solenoid driver converts the digital switch signal of the safety control system into a feed current. The communication with the intelligent field device is independent of the valve status which is defined as a 4 mA ... 20 mA signal that is overlaid by the HART communication.

• The communication with intelligent valves is independent of the valve position.
• The partial stroke test can be executed even in case the valve is in OFF-mode.
• Complete diagnostic information is available at any time.
• The usage of a common 2-wire-connection saves costs and reduces wiring effort.
• The solenoid driver meets all SIL 3 requirements according to IEC 61508.