User Manual

SAFETY
Safety handbook page - 18 -
PNSPO
5.0 Door monitoring and interlocking
Door monitoring and interlocking switches are one of the most important types of
protective devices to prevent dangerous situations by taking power off from the
machine.
When it is decided to protect the machine with protective fences, we must be sure that,
only way inside the dangerous area is through the guard. If the guard is opened,
mechanically actuated position detector stops the machine. In every guard in the fence
must have mechanically actuated position detectors (safety limit switches) to ensure
the safety of personnel. Basic requirement is that if the door is opened, machine must
stop before anyone can reach the hazardous moving parts of the machine.
The most important selection criteria of an interlocking device are:
•
the conditions of use and intended use (EN292-1)
• the hazard present at the machine (EN292-1)
• the severity of the possible injury
• the probability of failure of the interlocking device
• stopping time and access time considerations
•
the frequency of access
• the duration of person exposure to the hazard
• performance considerations
The position switch shall be actuated in the positive mode. The break contact of the
position switch shall be of the “positive opening operation” type. (EN 60947-5-1)
The security of an interlock switch is dependent on its ability to withstand attempts to
“cheat” of defeat the mechanism. An interlock switch should be designed so that it
cannot be defeated in a simple manner. This means that intended operation achieved
manually or with a readily available abject. Readily available objects may be:
• screws, needles, sheet-metal pieces;
• objects in daily use such as keys, coins, tools required by the intended use of the
machine
5.1 Standards EN 1088, EN 1037
The European standard EN1088 “Interlocking devices associated with guards” gives a
guidance of interlocking devices and it is intended to be used together with
EN60947-5-1 for electromechanical switches and EN1037 “Prevention of unexpected
start-up“.