At a Glance. Machine guarding questions reach us in one of two forms: someone needs a door to be safe, or someone needs a space to be safe. Those are different problems with different standards, and picking the wrong technology is expensive to correct later. Interlocking devices — the family behind the Schmersal safety switch range such as RSS16-I2-D-R-SK, VWS21.1 and TS 336-02Z-M20 — stop a machine when a guard is opened. Electro-sensitive protective equipment — the family behind products such as the SLC440COM safety light curtain — stops a machine when a person enters a monitored field. Most guards listed in safety door switches and safety light curtains belong to one of those two groups.
1. Start from the hazard, not from the catalogue
Before a part number is chosen, three questions define the answer:
- Does the operator need physical access? If the only way to reach the hazard is to open a door, an interlocking device is the natural fit.
- Does the operator need to reach through a gap, or pass through regularly? Frequent material transfer or a walking route points to a light curtain or a safety laser scanner.
- What performance level is required? The risk assessment assigns a required PL or SIL, and that in turn constrains the architecture — single channel, dual channel, coded actuators, monitored outputs.
2. Interlocking safety switches at a glance
Interlocking devices are split by how hard they are to defeat, and standards are strict on this point because a bypassed guard is the classic cause of an accident.
| Type | How it works | Practical fit |
|---|---|---|
| Mechanical, uncoded | Separate actuator inserts into the switch head | Simple hinged and sliding guards, lower risk levels |
| Magnetic / coded | Magnet or coded sensor pair, no mechanical wear | Where alignment is difficult and dust or chips are present |
| RFID / uniquely coded | Electronic coding evaluated by the sensor | High-risk guards, where defeating prevention is essential |
| Guard locking | Guard held closed until a signal releases it | Guards that must stay shut while the hazard runs down |
Representative part numbers from our stock include RSS16-I2-D-R-SK (Schmersal order no. 103010485) and VWS21.1 (order no. 101023721), both belonging to the safety door switch and magnetic switch group. Mechanical position switches such as TS 336-02Z-M20 (order no. 151165264) are frequently used in the same application, either as the guard interlock or as a position-status signal. Always confirm the coding type, performance level and IP rating on the manufacturer datasheet for the exact variant you intend to install.
3. Light curtains and other opto-electronic guards
A safety light curtain protects an opening without a physical barrier. Its two defining parameters are resolution — the smallest object it will detect, which decides whether it protects fingers, hands or a whole body — and protective field height, which must cover the full opening. Add a muting function when pallets or material have to pass through the field without stopping the machine.
Typical applications where a curtain beats an interlocking switch:
- Automatic feed openings that are loaded by conveyor or robot
- Positions where operators reach in several times per shift and door cycles would slow production
- Perimeter guarding where a walking route must be detected rather than blocked
4. Decision table
| Situation | Recommended technology |
|---|---|
| Hinged guard opened only for maintenance | Interlocking switch, optionally guard locking |
| High-risk hazard, defeating must be prevented | Coded or RFID-coded interlocking device |
| Frequent manual loading of a small opening | Light curtain with suitable resolution |
| Automatic material transfer through the field | Light curtain with muting |
| Large area with several access routes | Safety laser scanner plus interlocking devices on doors |
| Guard position must be reported to the PLC | Switch with separate position and safety contacts |
5. What to send us for a quotation
- The existing part number and order number, plus a photo of the device label
- Required performance level and whether a coded or uncoded version is mandatory
- Mounting details: hinge side, approach direction, cable entry position
- For curtains: protective field height, resolution and the safety output type expected by the controller
Schmersal has issued a long series of replacement generations, and two devices with similar model numbers can differ in coding, contact arrangement and connector style. Our team resolves those differences from the order number rather than the model name, which is why the order number on the label is the single most useful piece of information you can send. Browse the full Schmersal range or the light curtain and safety switch categories to see current availability.