- RFID and magnetic safety switches
- Technology
Safety door switches technology explained
Functional safety standards
In manufacturing, there is no such thing as zero risk. Risk can be evaluated and reduced to a tolerable level. “Functional safety” involves determining how much harm a situation can cause and control it by means of safety-related devices.
ifm cannot perform risk assessment on applications. We promote light curtains and grids with the highest protection ratings:
- Type 4
- SIL 3
- SIL cl 3
- PL e
There are several standards for machine safety.
- IEC 61508 is an international standard for functional safety for electric, electronic and programmable electronic devices. It defines the requirements for design, operation and maintenance of systems to meet a certain Safety Integrity Level (SIL). It is the reference standard, but other sector-specific standards are derived from IEC 61508.
- ISO 13849-1 defines the requirements for Performance Level (PL) for electric, electronic and programmable electronic devices specifically for machinery.
- IEC 62061 defines the requirements for Safety Integrity Level claim limit (SIL cl) for electric, electronic and programmable electronic devices as well as non-electrical machinery such as hydraulics and pneumatics.
- IEC 61511 defines the requirements for Safety Integrity Level (SIL) for process automation.
- IEC 61496-1 and -2 define the requirements specifically for photoelectric devices like light curtains and grids (Type).
Coding levels
Coding of door switches/actuators provide different levels of tamper-resistance and safety.
Uniquely coded actuators
When the actuator leaves the factory, it is permanently paired with a sensor and cannot be modified. Defective products must be replaced as a pair. This is the highest level of coding and is offered in RFID door switches only.
Codable actuators
During installation, the actuator is programmed and assigned to a specific sensor. Actuators can be reprogrammed as necessary and defective products can be replaced individually. This level of coding is offered in RFID door switches only.
Coded actuators
The actuator is not assigned to a specific sensor. All ifm sensors detect each ifm actuator. Defective products can be replaced individually as necessary. This level of coding is offered in both magnetic and RFID door switches.
Comparison of RFID and magnetically coded safety switches
Both RFID-coded and magnetically-coded safety switches operate without physical contact and are, therefore, maintenance free.
 |
 |
|
| RFID-coded safety switch | Magnetically-coded safety switch | |
|---|---|---|
| Coding level | +++ | + |
| Series connection | +++ *Up to 32 with same safety integrity (Only for codable and uniquely coded sensors!) |
+ *Up to 32 with reduced safety integrity |
| Sensing range | +++ | ++ |
| Display and LED | +++ | - |
| Service life | +++ | ++ *Reed contacts have limited life |
| Cost | + | +++ |
Principle of operation - RFID-coded switches
The RFID-coded safety sensor (MN7xxS series) transmits a high-frequency magnetic field with an identification number. The actuator senses the signal and transmits its identification number. The sensor receives the actuator’s identification number and sets the output as shown.
If the two identification numbers match: (Fig. 1)
Output = 1 and the door is closed
Fig. 1
If the two identification numbers do not match (Fig. 2)
Output = 0 and the wrong actuator is detected
Fig. 2
Principle of operation - Magnetically-coded switches
Magnetic door switches consist of 2 reed switches. Sensor consists of 2 reed switches.
- If the magnetic fields from an actuator are not present (Fig. 1), both reed switches are open.
Output = 0
Fig. 1
- If the magnetic fields are present (Fig. 2), both reed switches are clsoed.
Output = 1
Fig. 2
- Both reed switches must be clsoed for the output to switch.