1. Introduction: The Imperative Need to Modernize Industrial Safety
Operational safety in industrial environments is a non-negotiable factor, constantly evolving driven by technological advances, stricter regulations and the search for greater efficiency. Legacy safety systems, based on individual safety relays, often have significant limitations in terms of flexibility, diagnostic capability and maintenance costs. Modernization, through the integration of SIL 3 certified programmable safety controllers (PSCs), is not just an option, but an essential strategic investment.
Outdated systems can lead to unacceptable risks, hidden failures, and prolonged downtime. The Machinery Directive 2006/42/EC underlines the importance of maintaining equipment in compliance with the latest safety standards. Furthermore, regulations such as UNE-EN ISO 12100 require continuous risk assessment and the implementation of solutions that minimize said risks. The update to modern technology not only meets these demands, but also optimizes production processes.
2. Evaluation of Legacy Systems: Identifying Critical Points
Before any retrofit process, it is essential to conduct a thorough evaluation of the existing security system. This assessment identifies deficiencies, potential risks, and areas where modernization will have the greatest impact. A detailed analysis must consider the following criteria:
| Evaluation Criteria | Description | Key Indicators |
|---|---|---|
| Antiquity and Obsolescence | Components with exceeded useful life or difficulty in finding spare parts. | Manufacturing date, parts availability (MTBF > 50,000 hours for older components), frequent interruptions. |
| Regulatory Compliance | Adherence to current standards (EN ISO 13849-1, EN IEC 62061). | Declared Performance Level (PL) or Safety Integrity Level (SIL) vs. requested. |
| Wiring Complexity | Extensive point-to-point wiring, making fault detection difficult. | Fault diagnosis time (> 2 hours/incident), complex electrical diagrams. |
| Limited Functionality | Difficulty integrating new features or making changes to security logic. | Lack of real-time diagnostics, impossibility of modifications without rewiring. |
| Maintenance Costs | High costs associated with troubleshooting and replacement parts. | Annual cost of spare parts (> €500/machine), hours of labor in corrective maintenance. |
| Impact on Productivity | Frequent unplanned stops or production slowdowns. | Hours of downtime due to security failures (> 80 hours/year), cost per hour of downtime (> €500/hour). |
3. Modern Alternatives: Programmable Safety Controllers (PSC)
The transition from hardwired safety relays to PSCs such as the SKF KH7D45 (functional equivalent in the area of SIL 3 certified programmable safety controllers) offers substantial advantages. PSCs consolidate multiple security functions into a single programmable device, simplifying architecture and improving monitoring.
| Feature | Legacy Security Relay System | Programmable Safety Controller (PSC) - Ex. SKF KH7D45 (functional equivalent) |
|---|---|---|
| Architecture | Distributed, point-to-point wiring, fixed logic. | Centralized or modular, fieldbus communication, programmable logic. |
| Security Level | Typically PL c/d or SIL 1/2. Limited by wiring complexity. | PL e or SIL 3 (UNE-EN ISO 13849-1 / EN IEC 62061). Greater integration capacity. |
| Diagnosis | Basic, local status indicator. Manual fault detection. | Advanced, remote and real-time diagnosis, event logging, precise fault location. |
| Flexibility | Rigid, requires rewiring for logic changes. | High, allows reconfiguration of the logic via software, integration with PLC systems. |
| Energy Consumption | Higher (e.g. 500W for multiple relays). | Lower (e.g. 100W for centralized unit). |
| Mean Time Between Failures (MTBF) | Minor (e.g. 50,000 hours/component). | Significantly higher (e.g. 200,000 hours/unit). |
| Installation Cost | Lower for direct replacement, higher for new features. | Greater initial investment, less wiring and total start-up time. |
4. Calculation of Return on Investment (ROI)
The modernization of industrial safety represents an investment with a clear quantifiable return. Let's consider a typical production line in the manufacturing sector with the following parameters:
- Energy cost: €0.15/kWh.
- Maintenance labor cost: €40/hour.
- Cost per hour of inactivity (loss of production): €500/hour.
Current Scenario (Legacy Relays)
- Electrical consumption of the security system: 500 W (0.5 kW).
- Annual security system failures: 4 incidents.
- Average downtime per incident: 8 hours.
- Corrective maintenance hours per incident: 4 hours (diagnosis + repair).
- Annual cost of spare parts: €500/year.
Annual cost calculation of the legacy system:
- Energy: 0.5 kW * 8760 h/year * 0.15 €/kWh = 657 €/year.
- Inactivity: 4 incidents * 8 h/incident * €500/h = €16,000/year.
- Corrective labor: 4 incidents * 4 h/incident * €40/h = €640/year.
- Spare parts: €500/year.
- Total annual cost of the legacy system: 657 + 16,000 + 640 + 500 = €17,797/year.
Modernized Scenario (SIL 3 Programmable Controller, e.g. SKF KH7D45)
- Initial investment cost (hardware + engineering): €3,000 (controller) + €1,000 (engineering) = €4,000.
- Security system power consumption: 100 W (0.1 kW).
- Annual security system failures: 1 incident (due to increased MTBF and diagnostics).
- Average downtime per incident: 2 hours (rapid diagnosis by PSC).
- Corrective maintenance hours per incident: 1 hour.
- Annual cost of spare parts: €100/year (less need for replacement).
Calculation of annual costs of the modernized system:
- Energy: 0.1 kW * 8760 h/year * 0.15 €/kWh = 131.4 €/year.
- Inactivity: 1 incident * 2 h/incident * €500/h = €1,000/year.
- Corrective labor: 1 incident * 1 h/incident * €40/h = €40/year.
- Spare parts: €100/year.
- Total annual cost of the modernized system: 131.4 + 1,000 + 40 + 100 = 1,271.4 €/year.
ROI Analysis
- Annual savings: €17,797 - €1,271.4 = €16,525.6/year.
- Initial investment: €4,000.
- Payback Period: €4,000 / €16,525.6/year ≈ 0.24 years (approximately 3 months).
This analysis demonstrates that the investment in a programmable safety controller is recovered in an extremely short period, followed by significant savings and a substantial improvement in operational safety and machine availability. The “old system still works” objection ignores the high hidden costs associated with low efficiency, long downtime, and the risk of regulatory non-compliance.
5. Implementation Roadmap: Minimize Disruption
A successful implementation of a modernized security system requires meticulous planning to minimize production disruption:
Planning and Design (Weeks 1-4)
- Detailed Risk Analysis: Risk recertification according to UNE-EN ISO 12100 for the target machine, identifying all required safety functions and their associated PL/SIL.
- Component Selection: Choice of PSC (e.g. SKF KH7D45 or equivalent) and compatible sensors/actuators. UNITEC-D offers a wide range of certified components.
- Architecture Design: Creation of detailed electrical and logical schematics of the new system, including integration with the existing PLC.
- Programming: Development of security software following EN IEC 62061.
Provisioning and Preparation (Weeks 5-8)
- Procurement: Purchase of all necessary security components through certified suppliers such as UNITEC-D.
- Pre-assembly and Testing: Assembly of control panels and functional testing of the PSC in a test environment (staging), simulating the inputs/outputs of the machine.
Installation and Configuration (Weeks 9-10)
- Shutdown and Teardown: Safe shutdown of the legacy system during a scheduled production stop.
- Physical Installation: Assembly of the PSC and new sensors/actuators. The estimated installation time for a complex system can be 16 hours.
- Wiring: Connection of the new system, reducing point-to-point wiring thanks to fieldbus communication.
- Software Loading: Loading of the verified security program in the PSC.
Start-up and Validation (Weeks 11-12)
- Operation Tests: Exhaustive verification of each safety function, including emergency stops, guards and operating modes.
- Integration Tests: Confirmation of correct communication with the process PLC and other control systems.
- Documentation and Training: Update of technical documentation and training of operation and maintenance personnel on the new system.
6. Technical Challenges and Solutions During Retrofit
Modernization can present challenges, but they are surmountable with proper planning and technical expertise:
- Hardware Compatibility: Ensure that new sensors (e.g. photoelectric barriers compliant with EN ISO 13855) and actuators are compatible with the PSC. Solution: Choose components from recognized manufacturers that offer standardized interfaces (e.g. OSSD). UNITEC-D advises on the selection of compatible equipment.
- Software Integration: Communication between the PSC and the process PLC (e.g. Siemens S7, Allen-Bradley ControlLogix) can be complex. Solution: Use standard safety communication protocols (e.g. PROFIsafe, CIP Safety) and dedicated interface modules.
- Panel Space: Older control panels may not have space for the new hardware. Solution: Plan a compact PSC design, or consider an auxiliary panel. Modern PSCs are more compact than multiple relays.
- Resistance to Change: Staff may prefer the familiarity of the old system. Solution: Provide extensive training, highlight the benefits (easier diagnosis, fewer failures) and clearly document procedures.
7. Case Study: Modernization of a Hydraulic Press in an Automotive Plant
An automotive components manufacturing plant in northern Spain operated a hydraulic press with a relay-based safety system for more than 20 years. This system featured:
- An insufficient PL c (Performance Level) for the current risk assessment.
- A failure rate of 6 times a year, with each incident causing 10 hours of downtime (total 60 hours/year).
- An electrical consumption of the security system of 600W.
The company decided to modernize the system using a SIL 3 certified PSC. The total investment was €4,500 (€3,500 hardware + €1,000 programming).
Results After Modernization:
- Safety: The system achieved a PL e / SIL 3, meeting and exceeding current regulations.
- Reliability: Failure rate reduced to 1 incident per year.
- Downtime: Hours of downtime due to security breaches decreased from 60 to 2 hours/year.
- Energy Consumption: The electrical consumption of the security system was reduced to 120W.
- Diagnosis: Fault diagnosis time went from 5 hours to less than 1 hour per incident.
KPIs Before and After:
| KPI | Before (Legacy Relays) | After (PSC SIL 3) | Improve |
|---|---|---|---|
| Security Level | PL c | PL e / SIL 3 | Full compliance |
| MTBF Security System | ~4,000 hours | ~8,760 hours | 119% |
| Annual Inactivity | 60 hours | 2 hours | 96.7% |
| Annual Energy Savings | N/A | ~€600 | N/A |
| Total Annual Cost Reduction | ~€25,000 | ~€2,000 | ~92% |
8. Commissioning and Validation: Ensuring Integrity
The commissioning and validation phase is critical to ensure that the modernized security system functions as intended and complies with applicable standards. This process includes:
- Functional Tests: Verification of each safety element (sensors, PSC, actuators) individually and together. This includes activating all emergency stops, checking safeguards and simulating fault conditions to ensure a safe response.
- Electrical Measurements: Checking voltages, currents and insulation according to EN 60204-1 (Safety of machines - Electrical equipment of machines).
- Software Validation: Confirmation that the safety logic programmed into the PSC meets the design and risk assessment. This may require simulation tools and step-by-step testing.
- Generation of Validation Report: Detailed documentation of all the tests carried out, the results obtained and the declaration of conformity with the PL/SIL achieved (according to EN ISO 13849-2). This report is crucial for security audits.
- Final Acceptance: Signing of the acceptance protocol by production, maintenance and engineering personnel, confirming the safe and efficient operation of the new system.
9. Conclusion
Modernizing safety systems from legacy relays to SIL 3 programmable controllers is an indispensable strategy for any industry that aspires to operational excellence, regulatory compliance and sustainability. Beyond the legal obligation, it represents a smart investment that reduces operating costs, minimizes downtime and protects the most valuable asset: staff. By choosing partners with experience and certified components, you ensure a smooth transition and a safer, more efficient industrial future.
Discover the industrial safety solutions that UNITEC-D offers for your modernization in the UNITEC-D E-Catalog.
10. References
- EN ISO 13849-1:2015 - Safety of machines – Safety-related parts of control systems – Part 1: General principles for design.
- EN IEC 62061:2021 - Machine safety – Functional safety of electrical, electronic and programmable electronic control systems related to safety.
- UNE-EN ISO 12100:2012 - Machine safety – General principles for design – Risk assessment and risk reduction.
- Directive 2006/42/EC of the European Parliament and of the Council, of May 17, 2006, relating to machinery.
- SKF, «Application Guide for Programmable Safety Components», 2024 Edition.
- Spanish Association for Standardization and Certification (AENOR) – Industrial Safety Standards.
