<s>
A	O
heat	B-Algorithm
flux	I-Algorithm
sensor	I-Algorithm
is	O
a	O
transducer	B-Algorithm
that	O
generates	O
an	O
electrical	O
signal	O
proportional	O
to	O
the	O
total	O
heat	O
rate	O
applied	O
to	O
the	O
surface	O
of	O
the	O
sensor	O
.	O
</s>
<s>
Heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
are	O
known	O
under	O
different	O
names	O
,	O
such	O
as	O
heat	O
flux	O
transducers	B-Algorithm
,	O
heat	O
flux	O
gauges	O
,	O
or	O
heat	O
flux	O
plates	O
.	O
</s>
<s>
Some	O
instruments	O
are	O
actually	O
single-purpose	O
heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
,	O
like	O
pyranometers	O
for	O
solar	O
radiation	O
measurement	O
.	O
</s>
<s>
Other	O
heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
include	O
Gardon	O
gauges	O
(	O
also	O
known	O
as	O
a	O
circular-foil	O
gauge	O
)	O
,	O
thin-film	O
thermopiles	O
,	O
and	O
Schmidt-Boelter	O
gauges	O
.	O
</s>
<s>
Heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
are	O
used	O
for	O
a	O
variety	O
of	O
applications	O
.	O
</s>
<s>
There	O
are	O
various	O
examples	O
of	O
sensors	O
that	O
internally	O
use	O
heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
examples	O
are	O
laser	O
power	O
meters	O
,	O
pyranometers	O
,	O
etc	O
.	O
</s>
<s>
One	O
of	O
the	O
starting	O
points	O
in	O
these	O
studies	O
is	O
the	O
mounting	O
of	O
heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
on	O
walls	O
in	O
existing	O
buildings	O
or	O
structures	O
built	O
especially	O
for	O
this	O
type	O
of	O
research	O
.	O
</s>
<s>
Heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
mounted	O
to	O
building	O
walls	O
or	O
envelope	O
component	O
can	O
monitor	O
the	O
amount	O
of	O
heat	O
energy	O
loss/gain	O
through	O
that	O
component	O
and/or	O
can	O
be	O
used	O
to	O
measure	O
the	O
envelope	O
thermal	O
resistance	O
,	O
R-value	O
,	O
or	O
thermal	O
transmittance	O
,	O
U-value	O
.	O
</s>
<s>
Two	O
major	O
differences	O
however	O
are	O
the	O
fact	O
that	O
the	O
thermal	O
properties	O
of	O
a	O
wall	O
generally	O
do	O
not	O
change	O
(	O
provided	O
its	O
moisture	O
content	O
does	O
not	O
change	O
)	O
and	O
that	O
it	O
is	O
not	O
always	O
possible	O
to	O
insert	O
the	O
heat	B-Algorithm
flux	I-Algorithm
sensor	I-Algorithm
in	O
the	O
wall	O
,	O
so	O
that	O
it	O
has	O
to	O
be	O
mounted	O
on	O
its	O
inner	O
or	O
outer	O
surface	O
.	O
</s>
<s>
When	O
the	O
heat	B-Algorithm
flux	I-Algorithm
sensor	I-Algorithm
has	O
to	O
be	O
mounted	O
on	O
the	O
surface	O
of	O
the	O
wall	O
,	O
one	O
has	O
to	O
take	O
care	O
that	O
the	O
added	O
thermal	O
resistance	O
is	O
not	O
too	O
large	O
.	O
</s>
<s>
Also	O
,	O
in	O
walls	O
the	O
use	O
of	O
self-calibrating	O
heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
should	O
be	O
considered	O
.	O
</s>
<s>
A	O
difficulty	O
during	O
this	O
measurement	O
is	O
that	O
the	O
human	O
skin	O
is	O
not	O
particularly	O
suitable	O
for	O
the	O
mounting	O
of	O
heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
.	O
</s>
<s>
Heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
are	O
also	O
used	O
in	O
industrial	O
environments	O
,	O
where	O
temperature	O
and	O
heat	O
flux	O
may	O
be	O
much	O
higher	O
.	O
</s>
<s>
A	O
heat	B-Algorithm
flux	I-Algorithm
sensor	I-Algorithm
should	O
measure	O
the	O
local	O
heat	O
flux	O
density	O
in	O
one	O
direction	O
.	O
</s>
<s>
As	O
shown	O
before	O
in	O
the	O
figure	O
to	O
the	O
left	O
,	O
heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
generally	O
have	O
the	O
shape	O
of	O
a	O
flat	O
plate	O
and	O
a	O
sensitivity	O
in	O
the	O
direction	O
perpendicular	O
to	O
the	O
sensor	O
surface	O
.	O
</s>
<s>
For	O
better	O
understanding	O
of	O
heat	B-Algorithm
flux	I-Algorithm
sensor	I-Algorithm
behavior	O
,	O
it	O
can	O
be	O
modeled	O
as	O
a	O
simple	O
electrical	O
circuit	O
consisting	O
of	O
a	O
resistance	O
,	O
,	O
and	O
a	O
capacitor	O
,	O
.	O
</s>
<s>
Usually	O
,	O
the	O
thermal	O
resistance	O
and	O
the	O
thermal	O
capacity	O
of	O
the	O
entire	O
heat	B-Algorithm
flux	I-Algorithm
sensor	I-Algorithm
are	O
equal	O
to	O
those	O
of	O
the	O
filling	O
material	O
.	O
</s>
<s>
The	O
temperature	O
dependence	O
of	O
the	O
thermocouple	O
causes	O
the	O
temperature	O
dependence	O
and	O
the	O
non-linearity	O
of	O
the	O
heat	B-Algorithm
flux	I-Algorithm
sensor	I-Algorithm
.	O
</s>
<s>
Another	O
possibility	O
to	O
minimize	O
the	O
temperature	O
dependence	O
of	O
a	O
heat	B-Algorithm
flux	I-Algorithm
sensor	I-Algorithm
,	O
is	O
to	O
use	O
a	O
resistance	O
network	O
with	O
an	O
incorporated	O
thermistor	O
.	O
</s>
<s>
Another	O
factor	O
that	O
determines	O
heat	B-Algorithm
flux	I-Algorithm
sensor	I-Algorithm
behavior	O
,	O
is	O
the	O
construction	O
of	O
the	O
sensor	O
.	O
</s>
<s>
Summarizing	O
:	O
The	O
intrinsic	O
specifications	O
that	O
can	O
be	O
attributed	O
to	O
heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
are	O
thermal	O
conductivity	O
,	O
total	O
thermal	O
resistance	O
,	O
heat	O
capacity	O
,	O
response	O
time	O
,	O
non-linearity	O
,	O
stability	O
,	O
temperature	O
dependence	O
of	O
sensitivity	O
,	O
uniformity	O
of	O
sensitivity	O
and	O
sensitivity	O
to	O
lateral	O
fluxes	O
.	O
</s>
<s>
By	O
varying	O
the	O
hot	O
and	O
cold	O
sides	O
of	O
the	O
stack	O
,	O
and	O
measuring	O
the	O
voltages	O
of	O
the	O
heat	B-Algorithm
flux	I-Algorithm
sensor	I-Algorithm
and	O
temperature	O
sensor	O
,	O
the	O
correct	O
sensitivity	O
can	O
be	O
determined	O
with	O
:	O
</s>
<s>
While	O
heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
are	O
typically	O
supplied	O
with	O
a	O
sensitivity	O
by	O
the	O
manufacturer	O
,	O
there	O
are	O
times	O
and	O
situations	O
that	O
call	O
for	O
a	O
re-calibration	O
of	O
the	O
sensor	O
.	O
</s>
<s>
Especially	O
in	O
building	O
walls	O
or	O
envelopes	O
the	O
heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
cannot	O
be	O
removed	O
after	O
the	O
initial	O
installation	O
or	O
may	O
be	O
very	O
difficult	O
to	O
reach	O
.	O
</s>
<s>
The	O
interpretation	O
of	O
measurement	O
results	O
of	O
heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
is	O
often	O
done	O
assuming	O
that	O
the	O
phenomenon	O
that	O
is	O
studied	O
,	O
is	O
quasi-static	O
and	O
taking	O
place	O
in	O
a	O
direction	O
transversal	O
to	O
the	O
sensor	O
surface	O
.	O
</s>
<s>
The	O
case	O
that	O
the	O
heat	B-Algorithm
flux	I-Algorithm
sensor	I-Algorithm
is	O
used	O
as	O
a	O
radiation	O
detector	O
(	O
see	O
figure	O
to	O
the	O
left	O
)	O
will	O
serve	O
to	O
illustrate	O
the	O
effect	O
of	O
changing	O
fluxes	O
.	O
</s>
<s>
Generally	O
,	O
heat	B-Algorithm
flux	I-Algorithm
sensors	I-Algorithm
are	O
quite	O
slow	O
and	O
will	O
need	O
several	O
minutes	O
to	O
reach	O
95%	O
response	O
.	O
</s>
