
22-26 Electrical Variables
In the second step, an RF power P
RF
is fed to the sensor; the power increase must be compensated
by a dc po
wer
de
crease,
wh
ich
is pe
rformed
by lo
wering
th
e
br
idge
dc su
pply
vo
ltage
E; in th
is
ca
se,
le
tI
be eq
ual
to I
2
.
Si
nce
th
e
po
wer
di
ssipated
in th
e
se
nsor
ha
s
be
en
ma
intained
co
nstant
in bo
th
st
eps,
th
e
po
wer
P
RF
ca
n
b
e
e
valuated
a
s
P
R
I I
RF
= −
( )
4
1
2
2
2
(2
2
.64
)
e
ma
nual bolometer with substitution method
(F
igure
22.31
)
co
nsists
of tw
o
se
quential
st
eps;
in th
e
r
st,
bo
th
RF po
wer
(P
RF
) and dc power (P
dc
) are present, and the power (P
d
) necessary to lead the bridge
to t
he
e
quilibrium
i
s
P P P
d dc RF
= +
(22.65)
Durin