The Schmersal SRB031MC series is a compact safety monitoring module (safety relay) specifically designed for signal processing of outputs connected to potentials (AOPDs), such as safety light grids and light curtains. It is also ideal for evaluating signals from contact-based safety devices like emergency stop command devices, safety position switches, solenoid interlocks, and magnetic safety sensors. With its ultra-slim 22.5 mm width and DIN rail mounting, it offers a space-saving solution for safety circuits in control cabinets.

This safety relay module supports STOP category 1, featuring an adjustable drop-out delay that can be set to 0.4, 0.7, 1.1, or 1.5 seconds via internal switches. It provides three safety contacts (3 NO) and one auxiliary signaling output (1 NC), ensuring reliable isolation and monitoring of hazardous machine motions. The SRB031MC meets the highest safety standards, including EN ISO 13849-1 (PL d / Category 3 for Stop 1) and IEC 61508 (SIL 3 for Stop 0 applications).

Key Features & Advantages

Comprehensive Safety Monitoring: The SRB031MC is suitable for both potential-free contacts (emergency stop, position switches) and active optoelectronic protective devices (AOPDs) like safety light grids. It integrates seamlessly into safety circuits for sliding, hinged, and removable safety guards.

Adjustable Drop-out Delay (STOP 1): The module supports STOP category 1 with a field-adjustable drop-out delay ranging from 0.4 to 1.5 seconds. Four preset time delays (0.4s, 0.7s, 1.1s, 1.5s) can be selected via internal DIP switches, providing flexibility for applications requiring controlled stopping.

High Safety Integrity: Certified to PL d (Stop 1) and SIL 3 (Stop 0), with a PFH_D value of 2.00 × 10⁻⁷ /h and a mission time of 20 years. The module complies with EN ISO 13849-1, IEC 61508, IEC 62061, and EN IEC 60947 series standards.

Robust Output Configuration: Features three safety contacts (NO) with Ag-Ni contacts, self-cleaning and positive drive mechanisms. Switching capacity: AC-15 (230 VAC / 6 A) and DC-13 (24 VDC / 6 A). Includes one auxiliary signaling output and two normally closed (NC) contacts.

Advanced Diagnostics and Protection: Built-in diagnostic functions include wire breakage detection, cross-circuit detection, earth leakage detection, and an electronic fuse. A feedback circuit ensures proper external contactor monitoring. Four LED indicators provide clear status of operating voltage, channel states (K1, K2), and internal operating voltage.

Flexible Start and Reset Options: Supports both automatic start and monitored start (start button) with integrated feedback circuit. The module also includes an automatic reset function and supports bridging of voltage drops up to 3.5 seconds.

Wide Operating Range and Rugged Design: Operates on 24 VDC or 24 VAC power supply. Designed for harsh industrial environments with an operating temperature range of -25°C to +60°C, storage temperature from -40°C to +85°C, and protection ratings of IP40 (housing), IP20 (terminals), and IP54 (mounting area).

Compact, Space-Saving Form Factor: With a width of just 22.5 mm, the SRB031MC is one of the most compact safety relays in its class, allowing high-density installation on DIN rails. Mechanical life exceeds 10 million switching cycles.

Technical Specifications Summary

• Standards Compliance: EN ISO 13849-1, IEC 61508, IEC 62061, EN IEC 60947-5-1, EN IEC 60947-5-3, EN IEC 60947-5-5, EN IEC 60204-1, EN IEC 60947-1
• Performance Level (Stop 1): PL d
• Category (Stop 1): 3
• Diagnostic Coverage (DC): > 60%
• Common Cause Failure (CCF): > 65
• Safety Contacts: 3 NO (positive drive)
• Auxiliary Contacts: 1 NC (signaling), 2 NC
• Contact Material: Ag-Ni, self-cleaning
• Switching Frequency (max): 1,200 /h
• Mechanical Life: 10,000,000 operations
• Terminal Type: Screw terminals, M20 x 1.5, rigid or flexible
• Wire Cross-Section: 0.25 mm² to 2.5 mm²
• Tightening Torque: 0.6 Nm
• Rated Impulse Withstand Voltage: 4 kV
• Overvoltage Category: III
• Pollution Degree: 2
• Shock Resistance: 30 g / 11 ms
• Vibration Resistance: 10-55 Hz, amplitude 0.35 mm
• Housing Material: Glass-fibre reinforced thermoplastic, ventilated

Applications

The SRB031MC series is ideal for a wide range of safety applications, including:

• Signal processing for safety light grids and light curtains (AOPDs)
• Emergency stop monitoring with cross-circuit detection
• Guard door monitoring for sliding, hinged, and removable safety guards
• Safety position switch and solenoid interlock evaluation
• Magnetic safety sensor signal processing
• Two-hand control systems requiring STOP 1 functionality
• Industrial machinery requiring controlled stopping with adjustable time delay