When the radiant energy emitte 1 from a disk source is measured by a radiationmeter located at any distance, it is important to have a knowledge of the relations between the radiant flux and the distance which are obtained from a structural dimension of the radiationmeter.
If the whole distance is devided into three regions to introduce the above-mentioned relations on a radiationmeter, a formula for the radiant flux 4, taking the distance as a variable is given for each region as follows:
(1)
l<
D≤
l(
R0+
r)/
a+
rΦ=π
r2J-
a2/
l2+
a2(φ, independent on the distance,
D) (2)
l(
R0+
r)/
a+
r<
D<
l(
R0-
r)/
a-
rΦ=2π
J∫
r0Z(
D,
x)
xdx=
K(D)J(3)
D≥
l(
R0-
r)/
a-
rΦ=π
r2JR02/
R02+
D2In treating the case (2), a proposed approximation is suggested by the author in calculating the function φ, instead of solving theoretically.
A graph is shown here for the radiant flux incident to the thermopile of the radiationmeter, in case the radiancy of a circular disc source equals unity, taking its radius as a parameter, which was made in applying the above-mentioned approximation.
The use of this graph is desirable for practice where the radiancy and total emissivity of a circular disc source are measured by a radiationmeter.
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