Siemens 3TK2834-1BB40 Safety Relay

The Siemens 3TK2834-1BB40 is a compact dual‑channel safety relay designed for monitoring emergency stop circuits, guard door switches, and safety light curtains in industrial automation. Operating on a 24 V DC supply, this relay provides a reliable safety function that, upon detecting a fault or activation, de‑energises the output contacts to stop hazardous motion. It meets Category 4 / SIL 3 / PL e requirements, making it suitable for high‑risk applications.

The relay features two input channels for redundant sensor wiring, ensuring that a single component failure does not compromise safety. It includes automatic or manual reset options, as well as a diagnostic output for feedback to the PLC. Its narrow housing (22.5 mm) saves panel space, and the LED indicators provide at‑a‑glance status of power, input, and output states. The 3TK2834‑1BB40 is designed for long service life and robust operation in industrial environments.

Technical Specifications

• Supply voltage: 24 V DC (allowable range 19.2‑30 V DC)

• Inputs: 2 channels (for dual‑channel sensors – e.g., NC contacts of emergency stops)

• Output contacts: 2 safety NO contacts (6 A at 250 V AC), 1 auxiliary NC contact (diagnostic)

• Safety integrity level: SIL 3 (IEC 61508), PL e (ISO 13849), Category 4 (EN 954-1)

• Response time: < 20 ms (typical)

• Reset modes: Automatic or manual (selectable via wiring)

• Diagnostic output: Solid‑state output (24 V DC, 50 mA) for fault indication

• Power consumption: 5 W (maximum)

• Operating temperature: -25°C to +60°C

• Dimensions: 22.5 x 90 x 110 mm (W x H x D)

• Mounting: DIN rail (35 mm)

• Certifications: CE, UL, cUL, TÜV, RoHS

Functional Capabilities

• Dual‑channel monitoring: The relay evaluates both input signals; if they disagree, the output is disabled, indicating a wiring or sensor fault.

• Cross‑short detection: Detects short‑circuits between input channels, ensuring a single fault does not prevent the relay from tripping.

• Start‑up test: Upon power‑on, the relay performs a self‑test and only allows machine start if all inputs are in the safe state.

• Expansion capability: Multiple relays can be cascaded to monitor multiple safety zones.

Typical Applications

• Presses and shears: Emergency stop monitoring with two‑hand controls.

• Conveyor systems: Guard door interlocking with positive‑opening contacts.

• Robotic cells: Safety light curtain integration to prevent access during motion.

• Packaging machinery: Safety relay for stop circuits in high‑speed equipment.

Installation and Wiring

Mount the relay on a standard DIN rail. Connect the 24 V DC supply to the A1 and A2 terminals. Wire the dual‑channel input contacts to the S11/S12 and S21/S22 terminals (using two normally closed contacts). The output contacts (13‑14, 23‑24) are connected in series with the machine's main contactor coil. The reset circuit (Y1‑Y2) can be wired for automatic or manual reset; for manual reset, connect a pushbutton across these terminals. The diagnostic output (Y1‑Y2, solid‑state) can be connected to a PLC input for remote monitoring. Use shielded cables for long input wiring to avoid noise.

Compliance and Standards

The relay complies with EN 60204‑1 (machine safety), EN 60947‑5‑1, and IEC 61508. It holds TÜV and UL approvals, and is RoHS compliant.

Conclusion

The Siemens 3TK2834‑1BB40 safety relay offers a compact, high‑reliability solution for implementing safety functions in industrial machinery. Its dual‑channel architecture, diagnostic capabilities, and compliance with stringent safety standards make it a preferred choice for machine builders and system integrators.