Safety switches
What is a safety switch?
Safety switches regulate controlled and safe access to machines and processes.
We supply very robust safety switches for the harshest industrial conditions, as well as compact modular switches with many different integrated control functions.
TüV
certified
Pld / Ple according to
EN/ISO 13849-1
Safety keys
against
containment
Safe door switches and interlocks
Our product range safety switches for doors offers a solution for any application where secure access is required.
Which safety switch do you need?
Ask our specialists
Why do we use safety switches?
Employers are legally responsible for the safety of their employees and contractors during operations. This makes the use of safety switches a requirement when working with machines and processes.
Safety switches are often used to ensure machine safety. The function of these safety switches is to prevent the operator from accessing moving parts or other potentially dangerous energies without safe detection (using safety contacts). As a result, it can be trusted that there is no risk of danger and/or injury when entering a safeguarded area.
Typically, safety switches are placed at guarded access points of machinery and equipment such as; doors, hatches and valves. The basic principle of most safety door switches is that they are redundant, which means that one fault cannot result in the loss of the safety function.
So many different safety switches for so many different applications
Depending on the type of process or machine, you need to choose the right safety switch. This varies between mechanical safety switches with and without interlock function, non-contact safety switches, safety switches for explosive atmospheres or stainless steel safety switches. To help you make this choice, we have listed different types of safety switches.
Do you need help? Use our step-by-step guide. Or contact us.
Safety interlocks that protect during run-down time
A standard safety switch generates a safe stop command when opening, for example, movable guarding. However, often the machine or plant has a run-down time. Machines with a run-out time are, for example, robots, mixers or presses. In this case, access may be obtained only after the run-down time has passed. For applications with a run-down time, you use safety interlocks. Safety interlocks keep the guard locked until the process has come to a complete stop.
Safety interlocks that protect during run-down time
Safety switches with tamper protection
For some applications, it may be a requirement to take safety measures against manipulation or overriding the safety switch. The measures that need to be taken to prevent manipulation are specified in standard EN ISO 14119, this standard describes, for example, using coded safety switches. By using RFID in safety switches, a (uniquely) coded connection can be created between the actuator and the switch, making the safety switch harder to override.
Safety switches suitable as tamper protection
Safety switches with an escape release
For machine safety applications in a safeguarded area with an obstructed view or for machines with full body access, the machinery directive ISO 12100 (2010) describes in §6.3.5.3 the application of an escape release. The B standard EN ISO 14119 §5.7.5 gives as an example for a reactive containment measure the use of an emergency release. By installing a safety switch with an emergency release, it is possible to leave the safeguarded area at any time. Activating the emergency release will immediately stop the machine even if the restart was unintentional.
Switches with an escape release
How to prevent entrapment with safety switches
According to EN ISO 14119 an emergency release has a reactive effect against entrapment. Personal safety keys (mechanical or RFID coded) offer the possibility to prevent entrapment and unintentional restarts. Using safety keys prevents the door or hatch from being locked or the machine from restarting until the key is inserted back into the safety switch.
Another solution against entrapment is to use retro-fit our mechanical interlock blocking switches to increase your machine safety at existing access doors.
Safety switches that prevent entrapment
Modular machine safety solutions
From an efficiency perspective, it is often desirable to combine several functions in one safety switch configuration. In addition to the options described above like an emergency release and safety keys, it is also possible to add simple machine controls like an emergency stop, access request, reset or a tag reader as an integrated module to these safety switches.
Modular safety switches
Mechanical Interlocks for hygienic applications
In both the food processing and pharmaceutical industries, hygiene is priority one. So all safety components used in these environments must also comply with hygiene requirements. Therefore, use 3-A certified safety interlocks specially developed for these types of applications. These interlocks are suitable for chemical washdown environments with high pressure and high temperature. 3-A hygienic interlocks therefore have flat stainless steel surfaces with rounded corners to prevent dirt accumulation. In addition, these hygienic safety switches have a very tight seal (IP69K).
Hygienic safety switches
Robust stainless steel safety switches for extreme applications
Safety switches are used in many different environments. There are applications where the environment is less friendly to safety switches with a standard plastic or steel-coated housing. These include environments with high humidity, exposure to chemicals in washdowns or very cold or hot environments. For these applications, the following requirements are set for the safety solutions: a very good IP value, large alignment tolerance of the operating tongue, right choice of material (stainless steel), large temperature range, impact resistant with a large holding force (Fmax). And in addition, the switch sometimes needs to be resistant to vibration and be designed to minimize the accumulation of dust and grit in the switch head.
Heavy Duty Stainless Steel Safety Switches
Safety switches with network functionality
Over the past decade, there have been significant developments in safety switches and interlocks for network control systems, such as ProfiNet and Ethernet IP. Machines require more and more functionality with complex logic. With network integrated safety switches, I/Os can be arranged more efficiently and installation and implementation costs can be significantly reduced.
Network Interlocks provide direct communication with Ethernet/IP & CIP Safety or PROFINET & PROFIsafe based systems for industrial safety and control. These network switches are available with various M12 and 7/8″ daisy-chain connection solutions.
As an addition, it is now possible to get network interlocks with PoE (Power over Ethernet), which brings even greater savings on integration, this way no junction boxes are needed and cabling can be further reduced.
Network safety switches
Safety switches for explosive environments
When safety switches are used in Ex environments, they are required to be designed so that there is no risk of explosion. The ATEX 114 standard describes the requirements for electromechanical components, in addition, the standard distinguishes between different Ex zones: Zone 0, Zone 1 and Zone 2 for gas explosions and Zone 20, Zone 21 and Zone 22 for chemical explosions.
The Ex marking on each component indicates the environment for which it can be used. This includes information relating to ambient temperature, Ex Zone, IP value and risk of sparking due to choice of material.
As an alternative to electromechanical Ex switches, a fully mechanical trapped key system can be used. When using this mechanical key system, the electrical insulation is placed outside the zone.
Atex safety switches
Choosing the right safety switch
Safety switches, also called “Interlocking devices associated with guards” in the standard, are available in many different versions. To help you choose the right safety switch for your applications, we have prepared the following checklist.
Step 1: Determine the right safety level
To select the right safety switch, it is necessary to first determine the risk level, using safety standards.
Two commonly used standards for machine safety are EN/ISO 13849-1 and ISO 62061. The combination of the risk assessment (RI&E) and these standards are used to determine the required safety level of the safety switch. Safety levels are expressed from PLa to PLe (according to EN/ISO 13849-1) or from SIL 1 to SIL 3 (according to ISO 62061).
SIL 3 or PLe safety switches offer the highest level of safety. These switches are designed for machines and processes where there is a higher risk of serious injury combined with frequent access. These safety switches are both electrically and mechanically redundant and ensure that 1 fault does not result in loss of safety function.
There are countless different machines, it is impossible to define exactly the requirements for each specific machine, therefore the European Union has created global legislation to comply with: the Machinery Directive 2006/42/EC.
Step 2: Does the machine have
a run-down time?
Yes > Safety switch or interlock
When the machine does not stop immediately after shutdown or isolation or when the response time between the safety switch and the safety controller i.c.w. the distance between the access point and the hazard is too short to ensure safe access, the safety switch must be equipped with an interlock function. This is called a solenoid interlock or safety interlock.
When using this type of safety switch, first an access request is made (on the switch or externally). Then, only after the expiry of the rundown time or standstill detection, the safety switch is unlocked.
In this case, use a mechanical safety switch with interlock.
No > Safety switch, safety sensor or process interlock
When the machine stops immediately after isolation, a safety switch without interlocking may be used, because opening the access point immediately disconnects/isolates the machine.
A type of safety switch where there is a mechanical connection between the head and the actuator (fixed and rotating). The retention force (holding force) ensures proper door closure and guaranteed alignment.
Also called a safety sensor is a type of safety switch whereby the transmitter and receiver are positioned opposite each other on the fixed and moving sides of an access point. When the receiver or actuator is moved out of range of the transmitter, the machine will be isolated. Different techniques are used in non-contact safety switches depending on the application;
Magnetic safety sensors
Magnetism-based non-contact sensors are the simplest way of securing your machines, this technology is robust, resistant to vibration and maintenance-free.
Coded magnetic safety switches
These safety sensors offer the convenience and maintenance of a standard magnetic safety switch. But offer more increased safety in the tamper and override areas. As a result, this type may be used as a low-coded interlock device according to EN ISO 14119:2013.
RFID coded safety switches (transponder)
This type of safety sensor uses RFID technology where a unique coding of each sensor can be chosen. The use of transponders in safety switches therefore ensures high coding according to EN ISO 14119:2013.
When the machine or robot has no run-down time but it is not desirable that the process is disturbed by opening an access point, you can choose a process interlock or magnetic interlock. This is a holding magnet (electromagnet) fitted with a coded non-contact safety sensor.
The electromagnet typically provides a holding force between 500N and 1000N, thereby preventing the unintentional opening of access points. Thanks to the tamper protection, safety magnetic interlocks provide maximum security for processes with no or short rundown time.
Step 3: Is there a risk of entrapment?
When there is full body access for an operator into a protected area, there is a risk of entrapment and an unintended machine restart. In order to prevent entrapment, the standard distinguishes two different types of preventive measures:
Re-active prevention
Entrapment can be prevented by providing a safety interlock with an emergency release function, where the access point can always be unlocked from the inside. In case of, for example, a fire or power failure. For example, a mechanical release button or lever on the inside of the protected area which operates the safety contacts and unlocks the interlock.
No > Safety switch, safety sensor or process interlock
Pro-active prevention
Unintended machine restarts can also be prevented by eliminating the possibility of a restart when an operator accesses the protected zone. The standard distinguishes the following type of proactive solutions for containment.
- Safety switch fitted with a safety key.
- Installing a personal safety padlock to prevent the safety switch from being turned on.
- A safe detection system like radar protection or laser scanners.
- Mechanical entrapment protection for doors or light barriers.
Step 4: Determine the environmental requirements
A. Watertightness or IP value
Depending on the environment, the right choice should be made regarding robustness, material and watertightness (IP value).
B. Construction shape and choice of material
Consider a safety switch with a metal housing, high tensile strength (Fmax) and a high alignment tolerance for heavy machinery with high vibrations and a lot of dirt.
For food processing and pharmaceuticals, you can use hygienic safety switches with a high IP value and full stainless steel housing.
For small packaging machines, compact safety switches or sensors are the most commonly used solution.
C. Explosive environments
In some industrial environments, there can be a risk of a gas or dust explosion. The ATEX directive provides guidance on the correct choice of safety switch.
There are 6 different ATEX zones:
- ATEX Zone 0 and 20: frequent or continuous risk of explosion (> 1000 hours per year)
- ATEX Zone 1 and 21: frequent or incidental explosion hazard present (< 1000 and > 100 hours per year)
- ATEX Zone 2 and 22: occasional explosion hazard present (< 10 hours per year)
Zones 20, 21 and 22 indicate the risk of dust explosion, while zones 0, 1 and 2 deal with the risk of gas explosion.
Step 5: BUS system type & connection
When there is full body access for an operator into a protected area, there is a risk of entrapment and an unintended machine restart. In order to prevent entrapment, the standard distinguishes two different types of preventive measures:
A. Conventional BUS system
This refers to all BUS systems where the safety switches are connected via a cable gland with terminals to the safe outputs of a safety PLC or safety relay. Because of redundancy, to achieve a safety category, each safety switch must be wired back to the PLC or relay.
Nowadays, it is possible to save on wiring in these systems by using safety switches with OSSD contacts, which allow switches to be placed in series without losing their safety function.
Choose for easy installation by using pre-wired plug connections (Quick Disconnects).
B. ASi Interface safety switches
ASi (Actuator Sensor Interface) interface safety switches are a type of safety switches that are compatible with the ASi system. The ASi system is a BUS system used for data exchange between sensors, actuators, and safety components.
An important feature of ASi interface safety switches is their ability to transmit and receive safety signals over the ASi network using a single 4-pole cable that is looped back to the ASi control system. This enables fast and reliable communication between the safety switches and the control components.
ASi interface safety switches often provide additional features such as diagnostic capabilities and monitoring of the safety status. This allows for quick detection of any errors or malfunctions in the system, enabling appropriate measures to be taken to ensure safety.
C. Network safety switches
Using safety switches with network integration (also known as industry 4.0) offers a wide range of benefits, including a smaller number of components, less wiring, fewer connections, faster installation and quicker commissioning.
It is also possible to monitor the status of each module for diagnosis and to better plan preventive maintenance.
Safety switches with integrated networking solutions are available in two different versions: ProfiNet & Profisafe, Ethernet IP & CIP Safety.
Integrate access protection, entrapment prevention and diagnosis of safety components with FRANK.
