<s>
A	O
proximity	B-Device
sensor	I-Device
is	O
a	O
sensor	O
able	O
to	O
detect	O
the	O
presence	O
of	O
nearby	O
objects	O
without	O
any	O
physical	O
contact	O
.	O
</s>
<s>
A	O
proximity	B-Device
sensor	I-Device
often	O
emits	O
an	O
electromagnetic	O
field	O
or	O
a	O
beam	O
of	O
electromagnetic	O
radiation	O
(	O
infrared	O
,	O
for	O
instance	O
)	O
,	O
and	O
looks	O
for	O
changes	O
in	O
the	O
field	O
or	O
return	O
signal	O
.	O
</s>
<s>
The	O
object	O
being	O
sensed	O
is	O
often	O
referred	O
to	O
as	O
the	O
proximity	B-Device
sensor	I-Device
's	O
target	O
.	O
</s>
<s>
Different	O
proximity	B-Device
sensor	I-Device
targets	O
demand	O
different	O
sensors	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
capacitive	B-Device
proximity	I-Device
sensor	I-Device
or	O
photoelectric	B-Algorithm
sensor	I-Algorithm
might	O
be	O
suitable	O
for	O
a	O
plastic	O
target	O
;	O
an	O
inductive	B-Algorithm
proximity	I-Algorithm
sensor	I-Algorithm
always	O
requires	O
a	O
metal	O
target	O
.	O
</s>
<s>
Proximity	B-Device
sensors	I-Device
can	O
have	O
a	O
high	O
reliability	O
and	O
long	O
functional	O
life	O
because	O
of	O
the	O
absence	O
of	O
mechanical	O
parts	O
and	O
lack	O
of	O
physical	O
contact	O
between	O
the	O
sensor	O
and	O
the	O
sensed	O
object	O
.	O
</s>
<s>
Proximity	B-Device
sensors	I-Device
are	O
also	O
used	O
in	O
machine	O
vibration	O
monitoring	O
to	O
measure	O
the	O
variation	O
in	O
distance	O
between	O
a	O
shaft	O
and	O
its	O
support	O
bearing	O
.	O
</s>
<s>
A	O
proximity	B-Device
sensor	I-Device
adjusted	O
to	O
a	O
very	O
short	O
range	O
is	O
often	O
used	O
as	O
a	O
touch	O
switch	O
.	O
</s>
<s>
Proximity	B-Device
sensors	I-Device
are	O
commonly	O
used	O
on	O
mobile	B-Application
devices	I-Application
.	O
</s>
<s>
Once	O
the	O
device	O
has	O
awoken	O
from	O
sleep	O
mode	O
,	O
if	O
the	O
proximity	B-Device
sensor	I-Device
's	O
target	O
is	O
still	O
for	O
an	O
extended	O
period	O
of	O
time	O
,	O
the	O
sensor	O
will	O
then	O
ignore	O
it	O
,	O
and	O
the	O
device	O
will	O
eventually	O
revert	O
into	O
sleep	O
mode	O
.	O
</s>
<s>
For	O
example	O
,	O
during	O
a	O
telephone	O
call	O
,	O
proximity	B-Device
sensors	I-Device
play	O
a	O
role	O
in	O
detecting	O
(	O
and	O
skipping	O
)	O
accidental	O
touchscreen	B-Device
taps	O
when	O
mobiles	O
are	O
held	O
to	O
the	O
ear	O
.	O
</s>
<s>
Proximity	B-Device
sensors	I-Device
can	O
be	O
used	O
to	O
recognise	O
air	O
gestures	O
and	O
hover-manipulations	O
.	O
</s>
<s>
An	O
array	O
of	O
proximity	B-Device
sensing	I-Device
elements	O
can	O
replace	O
vision-camera	B-Device
or	O
depth	B-Algorithm
camera	I-Algorithm
based	O
solutions	O
for	O
hand	B-General_Concept
gesture	I-General_Concept
detection	I-General_Concept
.	O
</s>
<s>
Top	O
dead	O
centre	O
(	O
TDC	O
)	O
/camshaft	O
sensor	O
in	O
reciprocating	O
engines	O
.	O
</s>
