Which Non-Contact Safety Switch is Right for Your Application?
Types of Non-Contact Safety Switches
Non-contact safety switches (also called non-contact safety interlock switches) can be grouped into four mainstream categories based on their sensing principles and construction.
1️⃣Magnetic (Reed or Hall) Non-Contact Safety Switches
• Principle: A permanent magnet and a reed switch or Hall element are coupled magnetically. When the guard is closed the circuit closes; when the guard is opened the circuit opens.
• Features: Low cost, simple construction, typical sensing distance 5–12 mm, resistant to dust and vibration, but low coding level (easily bypassed with a generic magnet).
• Typical series: Schmersal BNS 36, IDEC HS6B-M, SICK RE1/RE2, Omron D40Z-M, etc.
2️⃣RFID-Coded Non-Contact Safety Switches
• Principle: A reader head (RFID reader) is mounted on the frame and an actuator (RFID tag) on the guard. The reader recognizes a unique or grouped code to confirm the actuator is “authorized.”
• Features: Safety level up to PL e / SIL 3, sensing distance 8–15 mm (high tolerance), can be wired in series with 30+ units without fault masking.
• Typical series: SICK STR1, Pilz PSENcode, IDEC HS3A (multi-code / single-code), Omron D41D.
3️⃣Inductive (Eddy-Current / Electromagnetic) Non-Contact Safety Switches
• Principle: A high-frequency alternating magnetic field generated by a coil induces eddy currents in a metallic target (actuator), detecting distance changes.
• Features: Highly adaptable to metallic doors or surroundings, but limited coding; typically used for medium or low safety level or position monitoring.
• Typical series: Some vendors classify these as “proximity safety switches,” such as IFI, Turck NI series, etc. (in practice often grouped with magnetic types during selection).
4️⃣Photoelectric / Laser Non-Contact Safety Switches
• Principle: A light path is formed between emitter and receiver. When the guard is closed the light path is blocked or reflected by the actuator, changing the output state.
• Features: Long detection range (up to several meters), suitable for large guards or frameless designs, but sensitive to dust and moisture, requiring periodic cleaning.
• Typical products: Leuze OSSD photoelectric safety switches, some safety light curtains with integrated door-monitoring functions.
Additional Notes
• According to ISO 14119 (Safety of machinery – Interlocking devices associated with guards), the switches can also be classified by coding:
– Type 1: No coding (easily bypassed)
– Type 2: Low-level coding (simple grouped code)
– Type 3: High-level coding (unique pairing, prevents actuator replacement)
– Type 4: Unique full coding (key-lock principle, e.g., unique UID versions of RFID switches)
• When selecting, besides the sensing principle, consider safety level (PL/SIL), sensing distance, series-wiring capability, connector type, IP rating, and fault-masking prevention.
In summary, magnetic switches and RFID-coded switches are the two most widely used non-contact safety switch types today, while photoelectric and inductive types are used in specific applications.
