<s>
Safety	B-Algorithm
relays	I-Algorithm
are	O
devices	O
that	O
generally	O
implement	O
safety	O
functions	O
.	O
</s>
<s>
Relays	O
and	O
contactors	B-Algorithm
were	O
used	O
to	O
control	O
plant	O
and	O
machinery	O
in	O
the	O
early	O
days	O
of	O
control	O
technology	O
.	O
</s>
<s>
In	O
the	O
event	O
of	O
a	O
hazardous	O
situation	O
,	O
the	O
actuator	B-Algorithm
was	O
simply	O
isolated	O
from	O
the	O
energy	O
supply	O
.	O
</s>
<s>
Special	O
relay	O
circuits	O
,	O
such	O
as	O
the	O
three-contactor	O
combination	O
,	O
were	O
the	O
first	O
designs	O
to	O
come	O
out	O
of	O
deliberations	O
into	O
how	O
this	O
could	O
be	O
avoided	O
.	O
</s>
<s>
These	O
device	O
combinations	O
led	O
to	O
the	O
development	O
of	O
the	O
first	O
safety	B-Algorithm
relay	I-Algorithm
from	O
the	O
German	O
automation	O
manufacturer	O
Pilz	O
,	O
the	O
PNOZ	O
.	O
</s>
<s>
E-STOP	B-Device
,	O
safety	O
gate	O
or	O
standstill	O
monitoring	O
)	O
is	O
to	O
use	O
appropriate	O
measures	O
to	O
reduce	O
the	O
existing	O
risk	O
to	O
an	O
acceptable	O
level	O
.	O
</s>
<s>
As	O
such	O
,	O
safety	B-Algorithm
relays	I-Algorithm
monitor	O
a	O
specific	O
function	O
.	O
</s>
<s>
When	O
connected	O
to	O
other	O
safety	B-Algorithm
relays	I-Algorithm
,	O
they	O
guarantee	O
full	O
monitoring	O
of	O
a	O
plant	O
or	O
machine	O
.	O
</s>
<s>
The	O
design	O
technology	O
is	O
the	O
main	O
difference	O
between	O
the	O
safety	B-Algorithm
relays	I-Algorithm
:	O
</s>
<s>
Safety	B-Algorithm
relays	I-Algorithm
must	O
always	O
be	O
designed	O
in	O
such	O
a	O
way	O
that	O
,	O
if	O
wired	O
correctly	O
,	O
neither	O
a	O
fault	O
in	O
the	O
device	O
nor	O
an	O
external	O
fault	O
caused	O
by	O
the	O
sensor	O
or	O
actuator	B-Algorithm
will	O
lead	O
to	O
the	O
loss	O
of	O
the	O
safety	O
function	O
.	O
</s>
<s>
If	O
this	O
happens	O
,	O
the	O
machine	O
would	O
continue	O
running	O
if	O
the	O
operator	O
pressed	O
the	O
emergency	B-Device
stop	I-Device
pushbutton	I-Device
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
many	O
European	O
,	O
American	O
,	O
national	O
and	O
international	O
norms	O
and	O
safety	O
standards	O
prohibit	O
the	O
use	O
of	O
simple	O
relays	O
or	O
contactors	B-Algorithm
on	O
hazardous	O
machines	O
.	O
</s>
<s>
The	O
typical	O
design	O
of	O
a	O
first-generation	O
safety	B-Algorithm
relay	I-Algorithm
is	O
based	O
on	O
the	O
classic	O
three-contactor	O
combination	O
.	O
</s>
<s>
This	O
connection	O
is	O
used	O
to	O
check	O
and	O
monitor	O
the	O
position	O
of	O
actuators	B-Algorithm
,	O
which	O
are	O
activated	O
or	O
shut	O
down	O
via	O
the	O
safety	O
contacts	O
.	O
</s>
