SCHMERSAL SRB301MC – Dual-Channel Safety Relay Module | Emergency Stop & Guard Door Monitoring
Engineering Background
The SRB301MC is part of SCHMERSAL’s SRB modular safety relay platform — a field-proven series widely deployed across European and Asian manufacturing facilities for machine safeguarding applications. Designed to IEC 62061 and ISO 13849-1 standards, this relay module provides the safety integrity required for Category 4 / Performance Level e (PLe) architectures, making it suitable for the most demanding safety loops in industrial automation.
Product Positioning
The SRB301MC targets procurement engineers and machine builders who require a compact, DIN-rail-mounted safety relay capable of monitoring dual-channel emergency stop buttons, safety door switches, and light curtain OSSD outputs. Its force-guided relay contacts and cross-fault detection circuitry eliminate single-point failure modes, ensuring that safety functions remain effective even under component degradation conditions.
Complete Technical Specifications
| Manufacturer | SCHMERSAL GmbH & Co. KG |
| Part Number | SRB301MC |
| Series | SRB Modular Safety Relay |
| Supply Voltage | 24 VDC (±15%) |
| Input Channels | Dual-channel (2-channel monitored) |
| Safety Category | Category 4 per EN ISO 13849-1 |
| Performance Level | PLe |
| SIL Rating | SIL 3 per IEC 62061 |
| Safety Outputs | 3 NO (force-guided) + 1 NC (diagnostic) |
| Output Contact Rating | 6 A / 250 VAC; 6 A / 24 VDC |
| Response Time | ≤ 20 ms |
| Reset Mode | Manual monitored / Automatic (selectable) |
| Cross-Fault Detection | Yes |
| Mounting | DIN rail (EN 60715 / 35 mm) |
| Housing Width | 22.5 mm |
| Protection Class | IP40 (housing) / IP20 (terminals) |
| Operating Temperature | -10 °C to +55 °C |
| Storage Temperature | -25 °C to +70 °C |
| Weight | approx. 250 g |
| Certifications | CE, TÜV, UL, cUL |
| Standards Compliance | EN ISO 13849-1, IEC 62061, EN 60947-5-1 |
Proven Application Environments
- Emergency Stop Circuits — Monitors single or dual E-stop pushbuttons with cross-fault detection; compliant with EN ISO 13850.
- Safety Door & Guard Interlocking — Compatible with SCHMERSAL AZ/BNS series and third-party tongue-operated interlocks.
- Light Curtain & Safety Scanner Integration — Accepts OSSD (Output Signal Switching Device) inputs from Type 2 and Type 4 AOPDs.
- Two-Hand Control Panels — Supports Type IIIC two-hand control monitoring per EN 574.
- Robotic Cell Perimeter Guarding — Deployed in automotive body-in-white lines, welding cells, and collaborative robot (cobot) safety zones.
- Packaging & Food Processing Machinery — Stainless-steel-compatible wiring; suitable for washdown-adjacent control panels.
Engineering Advantages
- Force-Guided (Positive-Opening) Contacts — Mechanically linked NC/NO contacts prevent simultaneous closure, providing verifiable contact status for diagnostic feedback loops.
- Compact 22.5 mm DIN Profile — Minimizes control cabinet footprint; supports high-density safety relay arrays without additional bus modules.
- Selectable Reset Logic — Manual monitored reset prevents automatic restart after fault clearance; automatic mode available for non-hazardous applications.
- Wide Input Voltage Tolerance (±15%) — Maintains reliable operation across fluctuating 24 VDC bus conditions common in large panel installations.
- Diagnostic NC Output — Dedicated fault-signaling contact enables PLC-based monitoring of relay health without additional hardware.
- TÜV & UL Dual Certification — Satisfies both European Machinery Directive (2006/42/EC) and North American OSHA/ANSI requirements for global machine export.
System Architecture & Signal Flow
The SRB301MC operates on a dual-channel monitored input architecture. Under normal (safe) conditions, both input channels (S11/S12 and S21/S22) are closed, energizing the internal safety relay coil. The three force-guided NO safety outputs (13/14, 23/24, 33/34) close, enabling the downstream power circuit (motor contactor, valve solenoid, etc.).
Upon detection of an open circuit on either input channel, a cross-fault between channels, or a supply voltage dropout, the safety relay de-energizes within ≤20 ms. All NO outputs open simultaneously, interrupting the hazardous energy source. The NC diagnostic output (41/42) closes, signaling the fault condition to the supervisory PLC or HMI. The system remains in the safe state until a valid manual reset pulse is applied (in monitored reset mode), preventing unintended restart.
Typical wiring topology: E-stop → S11/S12 & S21/S22 → SRB301MC → Contactor coil K1/K2 → Motor drive enable.
Sourcing & Quality Verification
- Authorized Distribution Network — Konmask.com sources SCHMERSAL products through verified industrial automation distributors with documented supply chain traceability.
- Authenticity Assurance — Each unit ships with original SCHMERSAL packaging, holographic certification label, and factory test report where available.
- Inspection Protocol — Pre-shipment visual inspection covers housing integrity, terminal block condition, label legibility, and date-code verification.
- Counterfeit Risk Mitigation — SCHMERSAL’s TÜV-certified part markings and unique serial number ranges are cross-referenced against manufacturer databases prior to dispatch.
- Warranty — 12-month warranty against manufacturing defects from date of invoice; RMA process initiated within 48 hours of confirmed fault report.
Procurement Process
- Inquiry Submission — Contact support@konmask.com with your BOM line item, required quantity, and delivery timeline. Bulk pricing available for orders ≥ 5 units.
- Quotation & Lead Time Confirmation — Formal quotation issued within 1 business day; lead time confirmed based on current stock and inbound shipment schedule.
- Purchase Order — Submit PO referencing Konmask item number or SCHMERSAL part number SRB301MC. T/T, L/C, and PayPal accepted.
- Export Documentation — Commercial invoice, packing list, and certificate of origin provided as standard. FORM E (ASEAN-China FTA) available on request.
- Shipping — DHL Express / FedEx International Priority standard; sea freight consolidation available for large orders. EXW Xiamen / CIF destination negotiable.
- After-Sales Support — Technical datasheet, wiring diagram, and application note provided post-purchase. Remote commissioning support available via video call.
Technical FAQ
Q: Can the SRB301MC monitor a single-channel E-stop?
A: Yes. Bridge S11 to S21 and connect the single-channel device across S12/S22. Note that single-channel monitoring reduces the achievable safety category to Cat. 2 / PLd maximum.
Q: Is the SRB301MC compatible with SCHMERSAL’s Protect-IE safety bus?
A: No. The SRB301MC is a standalone hardwired relay. For fieldbus-integrated safety, refer to the SCHMERSAL SRB-E series with AS-Interface Safety at Work or Protect-IE modules.
Q: What is the maximum cable length for the input circuit?
A: SCHMERSAL recommends keeping input wiring below 100 m to avoid capacitive leakage currents that could mask a wire-break fault. For longer runs, use shielded cable and verify leakage current against the relay’s minimum input impedance specification.
Q: Can I use the SRB301MC with a 24 VAC supply?
A: No. The SRB301MC is rated for 24 VDC only. For AC supply applications, refer to the SRB301ST (115/230 VAC variant).
Q: How do I verify the force-guided contacts are functioning correctly?
A: Monitor the NC diagnostic output (41/42) via PLC digital input. If any NO output contact welds, the NC output will remain open even after the safety relay de-energizes, providing a detectable fault signal.
Q: What is the replacement / cross-reference for the SRB301MC?
A: Functional equivalents include Pilz PNOZ X3 (24VDC), Sick UE10-3OS, and Omron G9SA-321. Wiring diagrams differ; consult Konmask technical support before substitution.
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