DESIGN FOR SAFETY: ELECTRICAL AND CONTROL SYSTEMS


🌐 An Overview of Safety Standards

Manufacturers must remain focused on operator safety as they continue to increase automation in their factories. ISO 13849 and IEC 61508 lay out the requirements for the safety-related parts of control systems (SRP/CS) and electrical/electronic/programmable electronic safety-related systems, respectively, for high demand and continuous modes of operation.

πŸ”Œ Single vs. Dual Channel Structures

Safety circuits are vital components in automated machinery, designed to protect personnel and equipment from potential hazards. The ISO standard defines single-channel and dual-channel (or redundant) structures for electrical safety circuits, which are broken up into categories.

  • Category B: Category B is a single-channel circuit at the most basic performance level, using components that meet typical circuit conditions such as voltage and current ratings. These components must be suitable for the application and given environment. A single fault in the safety circuit could compromise the safety function of the device.
  • Category 1: Category 1 is similar to Category B in function but uses “well-tried safety principles” and “well-tried components” recognized by ISO or tested by their manufacturers to meet a component safety standard.
  • Category 2: This category employs periodic scans of the system to detect faults. The machine’s control system monitors the safety functionality and halts operation if a fault is detected. A loss of safety function could happen between scans.
  • Category 3: Category 3 is a dual-channel structure where a single fault in the circuit would not cause a loss of safety function due to redundancy. A comparison between single- and dual-channel structures is shown in Fig. 1.
  • Category 4: Category 4 is of the highest safety reliability, combining the structure of Category 3 with onboard diagnostics to monitor for faults. This category of safety circuit can maintain function with an accumulation of faults.

 

Fig 1. A typical emergency stop (e-stop) push-button with one normally open (NO) and two normally closed (NC) contacts. A single-channel structure (a) with one fault (failure to open) would result in a loss of safety protection, while the dual-channel structure of Category 3 or 4 (b) has a redundant input signal.

πŸ€– Safety programmable logic control (PLC) devices

Safety PLCs have the benefits of 1) reducing the size and complexity of wiring typically found with traditional safety relays and 2) simplifying future expansion and modification since physical infrastructure changes (e.g., rewiring and adding panels/components) are minimized. They are designed to provide control and safety measures for automated equipment and include programming dedicated to error detection. Safety PLCs continuously monitor input signal status to detect malfunctions and are held to high standards for software integrity and lifecycle testing.

πŸš€ MEMCO’s Delivers Safety and Reliability

MEMCO’s controls engineering team designs automation and robotic systems with your operators’ safety in mind using dedicated safety PLCs, dedicated safety input-output (I/O) modules, the latest robot safety system technologies, and Category 3-rated devices.

Contact us (https://memco.ai/contact) and see how we deliver safe, reliable machinery that complies with standards and best practices of the automated manufacturing industry.


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References

  1. ISO 13849-1:2023, Safety of machinery – Safety-related parts of control systems – Part 1: General principles for design. International Organization for Standardization (ISO).
  2. IEC 61508-1:2010, Functional safety of electrical/electronic/programmable electronic safety-related systems – Part 1: General requirements. International Electrotechnical Commission.