Abstract

Most thermopiles show a decrease in sensitivity when ambient temperature increases. By experimental study of the temperature dependence of the various factors which affect the sensitivity (radiation loss, gaseous conduction and convection loss, and losses through the solid supports) it has been determined that a major contributor to the effect at atmospheric pressure is the temperature coefficient of thermal conductivity of the thermocouple wires. Several ambient temperature independent thermopiles operating at atmospheric pressure have been made either by adjusting the size of the thermocouple wires or by addition of other solid conducting supports between the receiver and the cold junctions.

A mathematical analysis of the thermal system of a thermopile has led to a simplified formula for determining the proper materials and dimensions required to obtain ambient temperature independence. As a direct result of the analysis it can be stated that any thermopile, operated at atmospheric pressure, can be made ambient temperature independent by the proper choice of a thermal shunt between the receiver and the cold junctions. Limitations of the analysis are discussed. Experimental confirmation of the method is presented.

© 1951 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |
  • |
  • |

  1. U. S. Patent No. 1,553,789 (George Keinath).
  2. T. R. Harrison and W. Wanamaker, Rev. Sci. Instr. 12, 20 (1941).
    [Crossref]
  3. I. Amdur and N. L. Brown, Rev. Sci. Instr. 20, 435 (1949).
    [Crossref]
  4. Handbook of Chemistry and Physics, 1947 edition.
  5. U. S. Patent Reissue 19,564.
  6. W. G. Fastie and A. H. Pfund, J. Opt. Soc. Am. 37, 762 (1947).
    [Crossref] [PubMed]

1949 (1)

I. Amdur and N. L. Brown, Rev. Sci. Instr. 20, 435 (1949).
[Crossref]

1947 (1)

1941 (1)

T. R. Harrison and W. Wanamaker, Rev. Sci. Instr. 12, 20 (1941).
[Crossref]

Amdur, I.

I. Amdur and N. L. Brown, Rev. Sci. Instr. 20, 435 (1949).
[Crossref]

Brown, N. L.

I. Amdur and N. L. Brown, Rev. Sci. Instr. 20, 435 (1949).
[Crossref]

Fastie, W. G.

Harrison, T. R.

T. R. Harrison and W. Wanamaker, Rev. Sci. Instr. 12, 20 (1941).
[Crossref]

Keinath, George

U. S. Patent No. 1,553,789 (George Keinath).

Pfund, A. H.

Wanamaker, W.

T. R. Harrison and W. Wanamaker, Rev. Sci. Instr. 12, 20 (1941).
[Crossref]

J. Opt. Soc. Am. (1)

Rev. Sci. Instr. (2)

T. R. Harrison and W. Wanamaker, Rev. Sci. Instr. 12, 20 (1941).
[Crossref]

I. Amdur and N. L. Brown, Rev. Sci. Instr. 20, 435 (1949).
[Crossref]

Other (3)

Handbook of Chemistry and Physics, 1947 edition.

U. S. Patent Reissue 19,564.

U. S. Patent No. 1,553,789 (George Keinath).

Cited By

OSA participates in Crossref's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (7)

Fig. 1
Fig. 1

Thermopile for experimental study of ambient effects.

Fig. 2
Fig. 2

Radiation pyrometer for experimental studies.

Fig. 3
Fig. 3

Photomicrograph of ambient temperature independent thermopile with eight sets of junctions and nickel thermal shunt between receiver and mounting ring.

Fig. 4
Fig. 4

Comparison of performance of typical uncompensated and new thermopile.

Fig. 5
Fig. 5

Thermopile coefficients as a function of total losses through thermocouple wires. Arrowed points represent experimentally determined values.

Fig. 6
Fig. 6

Calculated voltage coefficient of the 2-mil chromel-constantan thermopile of Fig. 3 as a function of fractional loss through a nickel thermal shunt. Arrowed point represents experimentally determined value.

Fig. 7
Fig. 7

Differential thermopile.

Tables (3)

Tables Icon

Table I Effect of radiation loss and evacuation on output and temperature coefficient of thermopile in the ambient range from 80°F to 180°F.

Tables Icon

Table II Effect of ambient temperature and window material on minimum allowed source temperatures.

Tables Icon

Table III Comparison of Stefan-Boltzmann law with Newton’s law of cooling.

Equations (11)

Equations on this page are rendered with MathJax. Learn more.

E r = L g + L s + L r .
L g = G ( 1 + α T ) Δ T ,
L s = S ( 1 + β T ) Δ T ,
Δ V = ( A + C T ) Δ T
L r = R ( 1 + γ T ) Δ T
Δ V = E r ( A + C T ) G + S + R + ( G α + S β + R γ ) T .
C / A = ( G α + S β + R γ ) / ( G + S + R )
1 Δ V d Δ V d T = C / A - ( G α + S β + R γ ) G + S + R .
E r = a ( t s K s 4 - t r K r 4 ) ,
( K r 4 - K a 4 ) b ( 1 + α T ) Δ T .
G α + S β + R γ = 0