TESK-LA-12ST1 Double Contact Mechanical Interlock Switch IP67 Stainless Steel Machine Guard Lock

1. Product Overview

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The Schmersal TESK-LA-12ST1 is an advanced electromagnetic guard locking safety switch designed for the most demanding industrial safety applications requiring secure access control to hazardous machinery. It integrates robust ​guard door position monitoring, ​high-force electromagnetic locking (500 N holding force)​, and ​critical diagnostic feedback​ into a single, compact zinc die-cast housing rated ​IP67. This switch ensures a guard door (hinged or sliding) remains physically locked until the machine process has reached a verified safe state. Unlike basic interlock switches, the TESK-LA-12ST1 features sophisticated circuitry for ​Direct Opening Action​ and ​Diversity of Monitoring (D.O.M.)​, providing redundant diagnostics on both guard position and lock status. It consists of two parts: an actuator head (typically mounted on the movable guard) incorporating a high-security ​Type G coded magnet cylinder, and the switch body (mounted on the fixed frame) housing the solenoid lock, internal force-guided relays, and monitoring electronics. Its design is essential for complying with the strictest safety standards where unauthorized guard access poses severe risks.

​2. Key Technical Parameters

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Operating at ​24V DC (±10%)​, this safety-critical device features an electromagnetic lock delivering a secure ​500 N holding force, effectively preventing door opening under unsafe conditions. Electrical safety is managed by ​three Force-Guided Relays (FGR)​: 1 NC (Safety) + 2 NO (Monitoring/Auxiliary) channels rated for ​6A @ 250V AC / 10A @ 24V DC. It achieves the highest safety certifications: ​Performance Level PL e (ISO 13849-1, Category 4)​​ and ​Safety Integrity Level SIL 3 (IEC 62061)​. The ​Type G magnet coding​ offers substantial resistance against tampering and defeat. Key monitoring functions include:

• ​Position Monitoring (S2)​: Monitors guard closed position.
• ​Locked Status Monitoring (S3)​: Confirms lock bolt engagement.
• ​Diagnostic Monitoring (D.O.M.)​: Detects internal circuit discrepancies and component failures.
  Operating temperature ranges from ​​-25°C to +70°C. High-visibility ​LED indicators​ show power (yellow), guard closed/position (green), lock engaged (red), and diagnostic alerts. Its mechanical endurance exceeds ​1 million cycles, and locking adheres to ​EN ISO 14119 Type 4 (high safety) requiring Power-to-Unlock. M12 plug connectors provide standardized wiring.

​3. Primary Applications and Use Cases

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The TESK-LA-12ST1 is essential in high-risk applications where preventing guard access during dangerous machine cycles is paramount. It is widely deployed in ​industrial robot cells (welding, assembly, palletizing), large metal stamping/punching presses, plastic injection molding machines, automated CNC machining centers, and ​sensitive automated test/assembly equipment. Its high-security locking force is critical for guarding zones involving crushing, shearing, high-speed cutting, or processes with lengthy cycle times where premature access is catastrophic. Specific uses include securing robotic cell service doors, access hatches for material loading/unloading on presses, enclosures around robotic deburring stations, and perimeter gates guarding automated transfer lines. Its diagnostics are vital in complex machinery where differentiating between a safe guard closure and an unsafe condition (e.g., door closed but lock failed to engage) is necessary for preventing startup failures or hazardous situations. Environments include automotive plants, foundries, and heavy machinery fabrication.

​4. Product Advantages and Functional Benefits

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This switch offers significant competitive advantages:

• ​Highest Safety Integrity (PL e, SIL 3)​: Enables integration into the most critical Category 4 safety circuits.
• ​Enhanced Diagnostics (D.O.M.)​: Monitors lock position, guard position, and internal circuitry independently, providing superior diagnostic coverage and fault detection compared to standard switches.
• ​High-Security Locking (500 N)​: Actively prevents unauthorized access, ensuring personnel cannot open the guard until deliberately unlocked by the safety PLC.
• ​Tamper Resistance (Type G Magnet)​: Highly resistant to defeat using standard magnets or tools, improving security compliance.
• ​Robust Construction (IP67, Zinc Die-Cast)​: Ensures reliable performance in dirty, wet, or high-vibration environments.
• ​Clear Visual Status (Multi-color LEDs)​: Instant operator feedback on safety status (guard position, lock status, power, diagnostics).
• ​Power-to-Unlock Principle: Ensures the guard is only released upon a deliberate "safe" signal from the control system, eliminating accidental openings.
• ​Ease of Integration (M12 Connectors)​: Simplifies wiring and maintenance.

​5. Core Functionality and Monitoring

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The TESK-LA-12ST1 executes a sophisticated safety sequence. When the guard closes, the ​Type G coded actuator magnet​ signals the switch body, changing the state of the ​Safety NC contact (S1)​​ to indicate guard closure. Simultaneously, the ​solenoid locking bolt engages​ mechanically blocking the guard. Crucially, unlocking ​requires​ a deliberate ​24V DC signal​ from the safety PLC applied after confirming the machine has reached a safe state. The ​true power​ lies in its monitoring: The ​Position Monitoring (S2) NO contact​ confirms correct guard closure alignment. The ​Locked Status (S3) NO contact​ verifies the bolt is fully extended and engaged. The integrated ​Diagnostic Output Module (D.O.M.)​​ circuitry continuously cross-checks the functionality of S1, S2, S3, and internal components. If any discrepancy is detected (e.g., S1 says closed, but S2 detects misalignment; lock solenoid failure; internal circuit fault), the D.O.M. logic triggers the associated NO contact and illuminates the diagnostic LED. All monitored signals feed into the safety PLC, allowing it to precisely identify the fault condition, prevent unsafe start-up or operation, and guide maintenance, significantly enhancing machine safety and reducing diagnostic downtime.