To date, Curtis Instruments has provided declarations of conformity for its controllers against the Type C harmonised standard, EN1175-1:1998 Safety of Industrial Trucks. Of direct relevance to motor speed controllers used for vehicle traction and hydraulic pump control, clauses 5.94, 5.95, 5.97, and 5.98 call for the safety related control systems to be in accordance with EN954-1 category 1. Additionally, with direct relevance to electric steering controllers, clause 5.9.6 calls for the safety related control systems to be in accordance with EN954-1 category 3.
EN1175-1:1998 has been revised, and the new version EN1175-1:1998+A1:2010 references EN ISO 13849-1 instead of the old EN954-1 safety standard.
EN ISO 13849-1 has introduced many new aspects for functional safety of control systems. The integrity of a system or a sub-system is now stated as a Performance Level (PL), effectively replacing the familiar EN954-1 safety 'categories' of B, 1, 2, 3, and 4. The PL is derived by determining the Designated Architecture, the Meant Time to Dangerous Failure (MTTFd), and Diagnostic Coverage (DC%). The combination of these three criteria define the PL of a system or sub-system on the scale A, B, C, D, E, with A= lowest integrity and E= highest integrity. The Common Cause Failure (CCF) is not used in the determination of the PL, but indicates what measures have been taken to minimize CCF, and is scored 0 (poor) to 100 (excellent).
The first products to have been evaluated against the new EN ISO 13849-1 standard are the Curtis VCL AC motor controller family, namely Models 1238, 1236, 1234, and the new Model 1232. This work is not yet finalized but has progressed enough for us to provide the following preliminary data, to be confirmed later in 2011.
The new Curtis Model 1222 electric steering controller is designed in full accordance with EN954-1 category 3, and a declaration of conformity stating as such is available. This controller will be evaluated against EN ISO 13849-1 and the relevant data published later this year.