Schmersal PROTECT safety relay modules serve as core components of industrial safety control systems, fully compliant with EN ISO 13849-1 and IEC 61508 safety standards. They collect and evaluate signals from a wide range of safety sensors. The portfolio includes classic fixed-function SRB300/SRB400 series, new multi-functional SRB-E series, SRB-EXi explosion-proof modules and output expansion modules. Compatible with emergency stop pushbuttons, safety door switches, safety light curtains, rope pull switches and magnetic safety sensors, these modules support dual-channel fault detection, short-circuit monitoring and contactor feedback monitoring (EDM) to ensure safe machine shutdown under fault conditions. Both fixed-function and configurable multi-type variants are available for standalone machinery and complex automated production lines, achieving safety levels up to Cat.4 / PL e / SIL3.
20 mainstream models of Schmersal safety relay modules:
SRB301ST-24V
SRB301MC-24V
SRB301AN-24VAC/DC
SRB400NE-24V
SRB402NE-24V
SRB-E-302ST
SRB-E-402ST
SRB-E-201LC
SRB-E-301MC
SRB-E-402EM (Output Expansion Module)
SRB100DR-24V
SRB200Exi (Explosion-proof Version)
SRB101Exi (Explosion-proof Version)
SRB-E-204PE
SRB301LC/B-24V
SRB-E-302FWS-TS
SRB401EM-230V
SRB-E-212ST
SRB301STV.3
SRB-E-402FWS-TS
Typical application industries: injection moulding & die-casting machinery, stamping equipment, robot workcells, lithium new energy production lines, automated packaging lines, logistics sorting conveyor systems, port lifting machinery, mining conveying equipment, woodworking machinery, food & pharmaceutical processing machines, elevators & automated parking systems, printing machinery, tunnelling equipment, metallurgical production lines and chemical explosion-proof equipment. Common applications include safety gate interlock, emergency stop circuit monitoring, signal evaluation for safety light curtains, rope pull emergency stop systems and two-hand control circuits. These modules are essential components for machinery to meet CE machinery safety certification requirements.
Compared with conventional general-purpose relays, Schmersal safety relay modules feature five core advantages:
First, redundant hardware design for superior safety levels. Independent dual-channel circuits continuously perform self-tests to detect short circuits, cable breaks and contact welding. Safety outputs are forcibly cut off upon fault occurrence to prevent dangerous failure modes, reaching PL e and SIL3 for high-risk machinery applications.
Second, comprehensive product range for diverse working conditions. Classic fixed-function models are ideal for spare part replacement on legacy equipment. The new SRB-E multi-functional variants can be configured via rotary switches to realise more than ten safety logic modes, greatly reducing spare part varieties. Explosion-proof variants and output expanders are available for standard environments and hazardous chemical zones.
Third, advanced diagnostic functions simplify maintenance. Visible LED indicators distinguish operating status, activation triggers and fault codes to locate errors rapidly. Auto-reset and manual-reset modes are selectable, and integrated EDM function monitors the status of main contactor contacts in real time.
Fourth, compact DIN rail mounting and flexible wiring. The slim 22.5 mm housing saves cabinet space. Screw terminals and spring-cage terminals are optional. Wide-range AC/DC power supply and high electromagnetic compatibility ensure stable operation near inverters and high-power motors.
Fifth, wide compatibility and complete certifications. The modules support safety switches and light curtains from most manufacturers. Full TÜV and CE certifications are available; explosion-proof versions carry ATEX and IECEx approvals. Series connection enables expansion for multi-zone complex safety circuits, supporting standardized design for machinery manufacturers.
Standard general relays lack self-diagnosis and cannot satisfy modern machinery safety regulations. As the "brain" of safety circuits, Schmersal PROTECT SRB safety relays process signals from safety devices and execute safety logic. From single machine tools to large intelligent production lines, they build compliant and reliable safety control systems and deliver critical safety protection for automated equipment worldwide.
Related Safety Relays / Safety PLC
Browse the complete Schmersal Safety Relays / Safety PLC range. Representative models available through Glorient:
Safety relay modules are the core of a PL e / SIL 3 architecture. To understand how Category 3 and Category 4 circuits reach these levels, read SIL vs PL Explained: Performance Levels, Safety Categories and Component Selection.
Frequently Asked Questions
What is the difference between the SRB301/SRB400 and SRB-E series?
The SRB301 and SRB400 are classic fixed-function relays designed for a single safety function. The SRB-E series is configurable and can evaluate multiple sensor types - emergency stops, safety door switches, light curtains and magnetic sensors - in one compact unit with built-in diagnostics, making it more flexible for complex machines.
What is EDM (External Device Monitoring) and why does it matter?
EDM monitors the feedback contacts of the external contactors driven by the safety relay. If a contactor welds or fails to drop out, the relay detects the fault and prevents the machine from restarting, ensuring the safety circuit genuinely removes hazardous motion.
What safety levels can Schmersal safety relay modules achieve?
Depending on the wiring architecture and connected safety devices, Schmersal safety relays achieve up to Category 4 / PL e / SIL 3 in accordance with EN ISO 13849-1 and IEC 61508.