Safety Lock Circuits (LTspice + Explanation)
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Safety Lock Circuits (LTspice + Explanation) by Bee Technologies
Safety Lock Circuits (LTspice + Explanation)
- 1. Safety Lock Circuits (LTspice + Explanation) Generated on 2025-08-12 02:40:13 This document summarizes two circuits: (1) Simple single-relay safety lock with manual reset, and (2) ISO 13849 Cat.3/4-like dual-channel safety with monitored reset. Both LTspice netlists are included as separate .cir files in the same folder.
- 2. 1) Simple Safety Lock (Single Relay, Manual Reset) Use when risk level is low and formal Cat.3/4 is not required. Sensor is NC (closed in safe state). If the sensor opens (fault), the relay coil drops and the actuator is de-powered. Manual RESET is required to re-energize after any fault event. Netlist filename: simple_safety_lock_simple.cir In the netlist: S_SENS models the NC sensor, S_RESET models a momentary NO pushbutton, LCOIL/RCOIL model the relay coil, and S_K1 models the power contact closing once coil current exceeds a threshold.
- 3. Sensor (NC) RESET (NO) Relay Coil K1 K1 (NO) Power DC Actuator/Motor Simple Safety Lock Block Diagram
- 4. 2) Cat.3/4-like Dual-Channel Safety (Two Relays, Monitored Reset) Use when higher Performance Level (PL) per ISO 13849 is required. Two independent NC channels must both be safe for coils to energize. Two force-guided relays K1 and K2 provide series contact redundancy on the power path. Manual RESET is monitored via feedback (mirror) contacts; RESET is allowed only when both relays are fully dropped. Netlist filename: safety_lock_cat34_dual_channel.cir In the netlist: S_CH1/S_CH2 model NC safety channels, LCOIL1/2 are relay coils, S_K1/S_K2 are series power contacts, S_K1_FB/S_K2_FB model NC feedback used in the reset path.
- 5. Channel 1 (NC) Channel 2 (NC) RESET (Monitored) K1 & K2 Coils Feedback (NC) K1 + K2 (NO) in Series DC Actuator/Motor Cat.3/4-like Dual-Channel Block Diagram
- 6. Simulation & Implementation Tips To run: open each .cir in LTspice and run a Transient analysis. Waveforms are saved: coil currents, load voltage, and control signals. Edit PWL sources (VSENS_CTL, VCH1_CTL, VCH2_CTL) to create custom fault timings. Edit VRESET_CTL to change reset behavior. Replace abstract switches with vendor safety relays in real hardware. Ensure force-guided contacts and proper diagnostic coverage. Follow IEC 60204-1 and ISO 13849-1. For PL d/e targets, consider certified safety relays or safety controllers and documented MTTFd/DC calculations.