Which Non-Contact Safety Switch is Right for Your Application?

We explore the benefits of three different non-contact safety switches

Safety switches are indispensable in any application where safety is required for people and machinery. Commonly used to monitor doors, gates, and other moveable physical guards, safety switches of all varieties are used to separate personnel from a potential hazard. It sends a signal to the machine’s controls system if the guard has been opened, removed, or is out of alignment.

Non-contact safety switches are ideal in applications where precise guidance of guards may be difficult. These devices are typically long lasting, require minimal maintenance, and are resistant to shock and vibrations. By design, a non-contact safety switch generally consists of two pieces, a sensor and an actuator. Both never actually contact one another. SICK offers a large selection of non-contact safety switches, safety locking devices as well as traditional electromechanical safety switches and safety command devices.

When using a non-contact safety switch, it is a requirement for the machine to have the ability to stop fast enough because this type of switch will not prevent someone from opening a door. Small to medium machines typically have a faster stopping time. Machines with longer stopping times require a safe-locking device to ensure no one can open the door until the machine comes to a safe stop or speed. SICK offers three types of non-contact safety switches perfect for safe door monitoring applications.

Magnetic Non-Contact Safety Switches

With magnetic non-contact safety switches, there is up to a 9mm sensing range, which provides a fair amount of tolerance to account for many different situations. For example, if a door is sagging or slightly out of alignment, it is more accommodating to misalignment than a mechanical interlock. It is also tends to result in significantly less wear and tear because it has no contact with the actuator.

Magnetic safety switches from SICK, like the RE switches, can get up to performance level E, as long as you are using safety controls that have test pulses. The test pulses connect to the potential free contacts of the switch to reliably detect short circuits, either by using Flexi Soft or with ReLy safety relays.

However, if magnetic safety switches are wired in series, it could result in fault masking. This can be prevented by wiring the switches in series with Flexi Loop and the Flexi Soft programmable safety controller or by using an RFID non-contact safety switch with OSSD outputs. You can learn more about fault masking in our previous blog post.

RFID Non-Contact Safety Switches

RFID non-contact safety switches, like the STR1 from SICK, prevent manipulation of the guard. With magnetic non-contact safety switches like the RE series mentioned above, any actuator works with any sensor. That means someone could potentially carry a spare actuator with them to keep the door open while running the machine.

With high-coded versions of the STR1, the sensor will only work with the taught in actuator. A low-coded RFID safety switch operates similarly to the magnetic safety switch and is more easily manipulated. High-coded vs low-coded safety switches are discussed in Safety of machinery – Interlocking devices associated with guards – Principles for design and selection (ISO 14119:2013).

In addition, the STR1 RFID non-contact safety switches include OSSD outputs to detect short circuits. Rather than running test pulses from safe controls, OSSD outputs do that automatically. This allows you to cascade or wire the STR1 directly in series of up to 30 switches and not have to worry about fault masking.

However, the diagnostics are limited because the STR1 does not have communication over a BUS system like Flexi Loop does, but it can be connected to a Flexi Loop system to get that level of diagnostics. The advantage of the STR1 is that you can still cascade up to 30 different switches, even without using Flexi Loop.

RFID safety switches achieve performance level e and an IP69K rating with a 14mm sensing range, providing it a higher tolerance. With this higher tolerance, you can even gain accurate detection with, for example, a door that has a gap between the door and frame where it closes. The larger the sensing range, the lower the chances are for false trips to make sure machinery does not stop unexpectedly.

Lastly, the STR1 offers flexibility in mounting and operation due to three sensing areas from both sides and front. The RE magnetic safety switches only have one sensing surface. There are also four different actuator options: standard, flat, compact, and mini.

Magnetic Locking RFID Non-Contact Safety Switches

The last type of non-contact safety switch is used for the same type of applications, but primarily fixes issues with people opening doors and stopping machines mid-process to create unwanted downtime and material waste. Magnetic locking RFID non-contact safety switches provide the benefits of RFID non-contact safety switches with the added benefit of an energized magnet to keep a door closed.

The MLP1 safety switch can help to prevent all of this from happening with a magnet that reaches 500N if energized or 25N if de-energized. A level of 25N will keep the door closed, even if the magnet isn’t energized. This switch provides enough force for process protection, but does not guarantee people cannot open the door so it should not be used for people protection.

It has a high tolerance against misalignment, with a 5mm range in any direction. There is also a version with two pigtails for easy series connection that can be done without T-connectors. This is a unique feature to SICK’s MLP1 safety switch.

The MLP1 offers standard and integrated mounted options. The standard mounting option is simply surface mounting. An integrated mounting option can be mounted into the machine frame to keep it low profile. This is another unique feature exclusive to the MLP1.

In addition, the MLP1 has OSSD outputs that are monitored for short circuits and it is a performance level e device, regardless of safety controls. It can also easily be wired in series with Flexi Loop more comprehensive diagnostics.