If you are the user of the equipment, how do you properly propose reasonable safety control system PL (performance level) requirements to the supplier and verify whether the equipment meets the requirements after delivery?
If you are a manufacturer of equipment, when you see the technical requirements specifying a PLD requirement for the safety control system, how do you design a safety control system that meets the PLR ( Performance Level Required ) standard?
Safety control systems are a crucial method for risk reduction and play a vital role in mechanical safety design. GB/T 16855.1 / EN ISO 13849-1, as a replacement for EN 954-1 , is the primary safety standard applicable to the design of mechanical safety control systems. Due to the extensive content, we will present it in installments.
Key point! "Different" GB/T16855.1
Although it is a replacement standard for EN954-1, GB/T 16855.1 / EN ISO 13849-1 still has some unique features. Taking the Performance Level as an example, compared with the previous standard EN 954-1 which used a deterministic (reproducible) method, GB/T 16855.1 / EN ISO 13849-1 is based on a probabilistic method to evaluate safety control systems.
In addition to dealing with electrical, electronic and programmable electronic systems, GB/T 16855.1 / EN ISO 13849-1 also considers other control technologies, such as hydraulic transmission.
GB/T 16855.1 / EN ISO 13849-1 retains the categories validated in EN 954-1 , but also quantitatively assesses safety-related attributes using statistical calculation methods. These can be described by the following parameters:
◾ Category (Structure Requirements)
Mean Time Between Critical Failures ( MTTFD )
◾ Diagnostic coverage ( DC )
Common Cause Failure ( CCF )
Risk assessment/risk reduction and safety control system design
Risk assessment, risk reduction, and the design of safety control systems is an interactive process.
Figure 1. Risk Assessment and Risk Reduction
When protective measures to reduce risk require the use of control systems, the design requirements of the safety control system need to be considered.
Figure 2 Iterative Flow of Safety Control System Design
The design of a control system is actually an iterative process that requires multiple steps to complete.
As a safety expert, Pilz is the organizer of the 4th Working Group (Safety Control Systems) of the National Technical Committee on Standardization of Mechanical Safety. It has participated in and led the formulation and revision of many mechanical safety standards. In order to help everyone grasp the requirements of each standard more accurately, in addition to the important standard GB/T 16855.1 for safety control system design, interpretations of other important standards in the field of mechanical safety will be released in succession.
