faults in the individual safety circuits, which already have a certain PL. The
overall PL quoted for these devices is only attained, however, if also the whole
machine circuit under review lies within the scope of the respective PL.
The PL must always be considered in relation to a complete safety function and
not as applied to individual components or parts.
A guide for easily calculating the PL for a safety function consisting of several
individual components can be found in standard EN ISO 13849-1 chapter 6.3
and appendix H and I.
If safety components are being connected in series, the individual component
with the least PL determines the PL of the whole safety function. For example
a safety function consisting of 3 components, one with category 4 PL e, another
one with category 3 PL d and a third component with category 2 PL c will have
a PL c for the whole safety function. This means that a fault will lead to loss of
safety, although components with category 4 PL e are integrated into the safety
function, as one of the components being used has category 2.
When chaining several Performance Levels (PL) the overall PL can decrease,
see also EN 13849-1 standard chapter 6.3.
The proof of attainment of a safety category can take place with the aid of an
FMEA (Failure Mode and Effects Analysis). In this analysis 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.
Application of Hand-held Terminal
in special operation modes
For the manual control of machines in special operation 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 Hand-held Terminal has the advantage that the operator can get very close
to the operating area.
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, machine move‐
ments can also be set in motion with the Hand-held Terminal, knowingly or
unknowingly.
The machine operator, therefore, has to find the right compromise between
necessary flexibility and a reasonable limitation of the working range when se‐
lecting the corresponding cable length for the Hand-held Terminal.
It is not possible to limit the the working range of radio-operated hand-held
terminals by means of the cable. Therefore additional technical solutions are
required for these hand-held terminals.
If the machine or equipment is operated with the Hand-held Terminal, care must
be taken at this time to ensure that operation can only be controlled by the
Hand-held Terminal and cannot be operated from any other point on the equip‐
ment. The hazard zone may only be entered by the person who is operating
the Hand-held Terminal. If it should be necessary for more than one person to
work in the hazard zone at the same time, each person present requires an
enabling button and machinery movement may only be allowed after all the
enabling buttons have been activated.
Notes on the "emergency stop" but‐
ton
●
In theory, a perfectly designed machine should not require an emergency
stop button, because the Machinery Directive demands that a machine
must be safe throughout its lifetime and in all operation modes. In practice,
however, one is aware that unforeseen situations arise, in spite of all pre‐
cautions.
In order to enable a fast shutdown of the machine in these cases, or to
avert danger, an emergency stop button is provided on most machines.
The following figure shows that, a machine is permanently in the hazard
Bosch Rexroth AG
DOK-SUPPL*-VCH*08.1***-PR02-EN-P
Rexroth IndraControl VCH 08.1 Hand-held Terminal
40/117
Technical Data