Glossary · Functional safety
Safety-related part of a control system (SRP/CS)
Also known as: SRP/CS, safety-related part of control system
In functional safety of machinery, a safety-related part of a control system (SRP/CS) is a part of a control system that responds to safety-related input signals and generates safety-related outputs. Combined SRP/CS for input, logic and output perform a safety function.
- Functional safety
- Systems engineering
In one sentence
An SRP/CS is the part of a machine control system that handles safety-related inputs and outputs and is designed under ISO 13849-1.
Example
In a guard interlock on a CNC machine, the door switch, the safety relay and the two main contactors are the SRP/CS that together implement the safety function.
How it applies
- Functional safety: ISO 13849-1 applies to SRP/CS. They are typically split into input (sensor), logic and output (actuator) subsystems, each with its own Category, MTTFd and diagnostic coverage.
- Integrated systems: When machines are combined, an SRP/CS may span several machines, for example a line-wide emergency stop. Define the boundary and the responsible party.
- Technical documentation: Identify which components are safety-related in circuit diagrams and parts lists. Replacing them with non-equivalent parts invalidates the evidence, so the maintenance manual must flag them.
- Evidence: Every safety function should map to the SRP/CS that implement it.
SRP/CS vs. control system
The control system is the whole machine control. The SRP/CS is only the part that performs safety functions and receives the design and validation effort of ISO 13849.