CE Conformity, Directives and Standards
KeTop T50VGA
142
User's Manual, Version: 1.3
© KEBA 2007
14.2.6 Selection of Safety Categories in accordance with EN 954-1
The Machinery Directive demands that a fault in control circuit logic, or in-
terference or damage thereto, shall not lead to a hazardous situation.
This general approach is substantiated in EN 954-1 “Safety of Machinery,
Safety Related Parts of Control Systems“, which defines safety categories
(B, 1, 2, 3, 4) for control parts that are relevant to safety.
These categories apply irrespective of the technology employed, for exam-
ple to electrical, electro-mechanical or pneumatical systems.
The categories place qualitative requirements on the probability of failure,
the detection of faults and the performance of the controller in the event of
a fault.
The manufacturer of the machine selects the category dependent on the
actual hazard potential, which is determined from the hazard and risk
analysis.
For hazards that can cause irreversible injury or death, safety category 3 or
4 is usually required as a minimum. These categories require single fault
safety, which usually applies to multiple circuit technology in conventional
manner. It is also important in this context that individual faults are detected
in time to avoid a build up of faults, which may finally lead to loss of safety.
Faults that must be detected on electrical and electronic systems, for ex-
ample, are: cross circuits, cut-outs and sticking contacts.
Special certified safety control devices are often used to detect faults in the
individual safety circuits. The safety category quoted for these devices is
only attained, however, if also the whole machine circuit under review lies
within the scope of the respective safety category. The safety categories
must always be considered in relation to a complete safety function and not
as applied to individual components or parts.
The proof of attainment of a safety category can take place with the aid of
an FMEA (Failure Mode and Effects Analysis), in which all the faults that
could possibly arise are simulated, either theoretically or in practice, and it
is demonstrated that the requirements of the category are fulfilled.
14.2.7 Application of Handheld Terminals in Special Operating Modes
For the manual control of machines in special operating modes, where
safety depends on the timely reaction of the operating staff, it is absolutely
essential that the operator can overlook the operating area.
The handheld terminal has the advantage that the operator can get very
close to the control panel.
At the same time, the danger of misuse increases with mobility since, in
remote locations where it is not possible to observe the operating area,