EN ISO 14119 Safety of machinery - Interlocking devices associated with guards - Principles for design and selection

a. New subdivision of the interlocking devices (see note 1)

Type 1 devices - Uncoded

These can be:

• Rotary cam
• Linear cam
• Hinge

A: Movable guard - B: Actuator (cam) - C: Position switch - 1: Opening direction

Fig. 1 - Rotary camA: Movable guard - B: Actuator (cam) - C: Position switch - 1: Opening direction

Fig. 2 - Camme lineari

A: Movable guard - B: Actuator (cam) - C: Position switch

Fig. 3 - Hinge

Type 2 - Coded

These can be: (see Note 2):

• Position switch with codec tongue actuator
• Trapped key interlocking.

1: Position switch - 2: Actuator (shaped tongue)

Fig. 4 - Type 2 interlocking device - Coded

1: Switch - 2: Bolt lock

Fig. 5 - Trapped key interlocking

Type 3 - Unccoded

These can be:

• Inductive - Actuated by metal of the guard
• Magnetic - Actuated by uncoded magnet
• Capacitive - Ultrasonic or optical

Type 4 - Coded

These can be (see note 2):

• Magnetic - Actuated by coded magnet
• RFID
• Optical - Actuated by coded optics

1: Opening direction - 2: Type 4 interlocking device - 3: coded RFID tag actuator - 4: Movable guard

Fig. 7 - Type 4 interlocking device with position switch actuated by coded magnetic actuator

1: Opening direction - 2: Type 4 interlocking device - 3: coded magnet actuator - 4: Movable guard

Fig. 8 - Type 4 interlocking device - Coded

b. Overall system stopping performance and access time (The gards distance)

The access time shall be calculated by using the distance between the hazard zone and the guard together with the approcach speed (see ISO 13855:2010 for typical values).

c. Logical series connection of interlocking devices

Logical series connection of interlocking device means for NC contacts wired in series or for NO contacts wired in parallel.

Up to now, for a logical series of NC contacts, it is considered a DC = 60%, allowing you to get a PL d (not a PL e). The masking of faults, could lead to a lower diagnostic coverage, so nothing.

Based on DC = λdd / λd (ratio of detected dangerous failures and total) can easily lead to a DC <60%.

d. Interlocking devices based on “fault exclusion”

The standard specifies that the maximum safety level reached by interlocking devices based on “fault exclusion” is generally PLd. In fact there is the possibility that a single mechanical failure resulting in the loss of the safety function.

For example a mechanical failure relating to the key (actuator), or some part of the mechanical device can generate false information on the electrical contact output.

In some cases it is still possible reach the safety level PLe. These are cases of “fault exclusion for the guard locking”.

The safety level reached in these cases is not necessarily limited by the faults exclusion of the mechanical locking device.

However, specific requirements must be verified: the holding force specified (FZH) of the protection guard locking device must be sufficient to withstand static forces planned on locking bolt, it is also necessary to prevent any effect on the protection locking device determined by the forces dynamic due to movement of the protection guard.

e. Guard lock and Guard interlock

The standard emphasizes the fact that the interlock function and the lock function are two separate safety functions with PLR that can also be different (PLr Locking <PLr interlock)

f. Measures to prevent the defeat of the interlock device

Guards and protection devices of the machines should not be easy to by-pass or render non-operational (Directive 2006/42/EC §1.4.1). Measures required to minimize tampering.

Prevent access to the elements which constitute the interlock device:

• Mouting out of reach, physical obstruction / shielding, Mounting in hidden position)
• Preventing substitution of the actuators using encoded interlocking devices
• Prevent disassembly or moving of the interlocking devices (welding, gluing, riveting, etc ..)
• Status monitoring or cyclic testing of the intelocking device
• Adding an additional interlock device with a different principle of implementation. In this case, you will testing diving the plausibility of the state of both devices

The table 3 of the standard ISO 14119:2013 specify the additional measures against defeating interlocking devices depending on type.

The anti-tampering measures in case of magnetic sensors low level encoding(MAGNUS)

Mandatory:

• Mouting out of reach places, or mounting recesses and not visible in the machine, or status monitoring.
• Mounting the actuator so that it is difficult to remove

Advice:

• Second magnetic sensor
• Plausibility check of both sensors

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