13
SAFETY
PRECAUTION
Step
Three
Make
a
Fail
‐
Safe
System:
Design
a
fail
‐
safe
system
that
accommodates
the
possibility
of
switch
and/or
power
failure.
OMEGA
ENGINEERING
recommends
the
use
of
redundant
backup
systems
and
alarms
in
addition
to
the
primary
system.
Adding
a
redundant
high
level
float
switch
to
the
system
is
a
cost
effective
means
to
prevent
costly
tank
overflows.
All
of
the
powered
level
sensors
have
a
single
internal
relay.
The
normally
open
(NO)
or
normally
closed
(NC)
operation
is
user
selected
based
on
the
desired
system
control.
Always
design
a
fail
‐
safe
system
that
accommodates
for
the
possibility
of
functional
and/or
power
failure
to
the
instrument.
The
"normal"
relay
state
is
where
the
relay
coil
is
de
‐
energized
and
the
relay
indicator
is
OFF.
Therefore,
if
power
is
cut
OFF
to
the
switch
it
will
de
‐
energize
the
relay.
Make
sure
that
the
de
‐
energized
state
is
the
safe
state
in
your
system
design.
As
such,
if
switch
power
is
lost,
a
pump
will
turn
OFF
if
it
is
connected
to
the
normally
open
side
of
the
relay.