PROCESSING PROCEDURES 



When the index correction is added, Sverdrup's 

 formula for the total correction to protected 

 thermometer reading is: 



AT. 



(T'+V,)( .T'-t) 



'K-{T'+V,)-{T'-t) 



+ 1. 



The above formula may be simplified if used 

 for computing the correction directly. In the 

 denominator of the fraction shown above, Kis 

 usually 6100 or 6300, and the sum of the other 

 terms is roughly 100. Since most reversing 

 thermometers are read to hundredths of a degree 

 centigrade, the correction is desired to the same 

 accuracy. This accuracy can be obtained when 

 the denominator of the fraction is taken to be 

 K—100. Thus, an approximate formula for 

 the correction to be applied to the protected 

 thermometer reading to obtain water tempera- 

 ture in sitv is: 



AT = 



iT'+Vo){T'-t ) 

 K~-100 



+ /. 



The correction of unprotected thermometers 

 is more direct than the correction of protected 

 thermometers because the value of T^ has 

 already been determined. The expression for 

 thermal expansion is: 



C= 



(T.+ V.){T„~t„) 



where the only unknown on the right is T^. In 

 a development parallel to that given above for 

 the Sveidrup formula, letting Tu=T',-\~C, it is 

 found that: 



^"^ A'-(r„-u 



Tu—tu will not exceed 30° C, and may be 

 neglected in the denominator in comparison 

 with K. Including the index correction, the 

 practical formula for the correction to be applied 

 to the unprotected thermometer reading is: 



a7'= 



AT:+Vo){T„~t,) 



+/. 



Slide rule, graphs, or tables may be used as 

 aids in solving quickly the formulae for correc- 

 tion of both protected and unprotected ther- 

 mometer readings. A special slide rule has 

 been designed by D. L. Cole, utilizing the 

 approximate formula, with K— 1 00 and K as 

 divisors for protected and luiprotected ther- 

 mometers, respectively, to obtain the thermom- 

 eter correction, C. Figure 3 shows the design 

 of the rule for K=6100. The logarithmic 

 scales of the rule give respectively, T'-\-V„, 

 K or A'- 100, T'-t or T„-^, and C. For 

 example, if T' + Vo equals 112.1° C. for a 

 protected thermometer and T" — ^equals —10.6° 

 C, the thermometer correction may ])e found 

 by use of the rule as follows; Against T'-\-V, 

 (112.1) on the upper fixed scale is placed the 

 appropriate index mark (PROTECTED 

 THERMOMETER) on the upper edge of the 

 slide, and opposite T' — t (—10.6) on the lower 

 edge of the slide is read C (-0.20° C.) on the 

 lower fLxed scale. Sign of C is the same as 

 T'-t or T^-tu. 



For unprotected thermometers the "UN- 

 PROTECTED THERMOMETER" mark on 

 the upper edge and Tu,—tu on the lower edge 

 of the slide are used. 



Graphs and tables may be constructed for 

 general use in finding the expansion correction, 

 C, for any protected or unprotected thermom- 

 eter. A general table (table I) is given in part 

 II to find C for values of F„+ T' from 70° to 

 200° C. and T'-t from 0° to 25° C, using 

 ^■=6100. With this table or with the slide 

 rule the index correction, /, must be added 

 separately to get the total thermometer correc- 

 tion, AT. 



When processing a large quantity of data it 

 is advantageous to prepare individual graplis 

 or tables which incorporate the constant, Vo, 

 and include the index corrections, /, in the ther- 

 mometer scale. Such individual thermometer 

 correction tables or graphs are easier to use 



60 70 80 90 100 ] 150 



.l,.,,l....l.,..i„,.i„,l„.. i,.j:„i, .,i„j..i ,i . . . I 



PROTECTED THERMOMETER— »JI*- UNPROTECTED THERMOMETER 



,l...,l,,,.l,,,,l,,.,l,,.,l,.,.l. 



r*v.ot r.tv. 



-T — I — I — I — 1 — I — I— r 



41 c 



INDEX 



B i 3 456789 ^"l-'-loe '5 ^ 



I'l I'l r'l Hi)i | ili< | Si l l'|^i / i| J il| ^ft H | li/.|ilil| Uf | M i|ili ^Mfl|W |' l' ' vl '' nl '''|l' W" ' f"l''W I 'l I'l I' l i' i),|i H|i|| l., y i 



.04 .05 06 .08 .10 



.15 .20 



.30 .40 .50 60 .70 .80 .90 1,0 



Figuie 3. — Special slide rule for computing the expansion correction Cfor reversing thermometers (Al = 6100). 



