|The Machinery Directive 2006/42/EC and the replacement of EN954-1 with the EN ISO 13849-1 Safety Standard
The new Machinery Directive 2006/42/EC has replaced the Machinery Directive 98/37/EC. The directive has been extended in scope, and the requirements relating to risk assessment are now explicitly stated. Compliance with the new Machinery Directive 2006/42/EC is required before any industrial truck or similar vehicle can be legally marketed within the European Economic Area (EEA). It is the demonstration of compliance with Type B or harmonized Type C standards that allows manufacturers to claim automatic presumption of conformity with the Essential Health and Safety Requirements (EHSRs) contained in the Machinery Directive.
Under the new Machinery Directive, vehicle OEMs are required to perform and document a comprehensive hazard and risk analysis for all vehicle functions according to a Type C harmonized standard such as EN1175-1:1998+A1:2010, Safety of Industrial Trucks or, for vehicle types not covered by a Type C harmonized standard, a Type B standard such as EN ISO 13849-1 Safety Related Parts of Control Systems. This standard is the result of the significant revision of the old EN 954-1 safety standard, which according to the latest update from CEN (European Committee for Standardization) will cease to provide a presumption of conformity at the end of 2011.
In order to understand the new standard it is important to realize that it has two fundamentally different user types: 1.) the designer of safety related sub-systems, and 2.) the designers of safety related systems. In general the sub-system designer (a component manufacturer, such as Curtis Instruments) will need to provide the required data for the system designer to ensure that it is of adequate integrity for the system (the vehicle). This will usually require some testing, analysis, and calculation. The resulting data will be expressed in the format required by the standard as follows:
The system designer (the vehicle manufacturer) will then use this data to perform some relatively straightforward calculations to determine the overall Performance Level (PL) of the system.
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.
New declarations of conformity referencing EN ISO 13849-1 and EN1175-1:1998+A1:2010 will be made available for the controllers listed above, to provide presumption of conformity from Jan. 1, 2012 and beyond. Further, Curtis Instruments will develop future controller products for the industrial truck markets following the methodologies in full accordance with EN ISO 13849-1.