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Reference Tables for Platinum‐40% Rhodium/Platinum‐20% Rhodium Thermocouples
1.The following nomenclature is used in this paper. An alloy of, for example, 20 wt% rhodium in platinum is written as Pt‐20Rh. A thermocouple composed of two Pt‐Rh alloys is written, for example, Pt‐40Rh/Pt‐20Rh, which is frequently abbreviated to 40/20, etc. The positive member is always written first and the solidus separates the positive member from the negative member.
2.R. E. Bedford, Rev. Sci. Instr. 35, 1177 (1964).
3.R. C. Jewell, E. G. Knowles, and T. Land, Metal Ind. London 87, 217 (1955).
4.F. R. Caldwell, J. Res. Natl. Bur. Std. 10, 373 (1933).
5.E. D. Zysk, Engelhard Ind. Tech. Bull. 1, 8 (1960).
6.Temperature, Its Measurement and Control in Science and Industry, edited by C. M. Herzfeld and A. I. Dahl (Reinhold Publishing Corporation, New York, 1962), Vol. III, Part II, p. 154, Table 10.
7.E. D. Zysk, Engelhard Ind. Tech. Bull. 5, 69 (1964).
8.Data supplied by Johnson, Matthey and Co. with the purchased wire, 1964.
9.P. D. S. St. Pierre, Bull. Am. Ceram. Soc. 39, 264 (1960).
10.B. E. Walker, C. T. Ewing, and R. R. Miller, Rev. Sci. Instr. 33, 1029 (1962);
10.[and also note Erratum: B. E. Walker, C. T. Ewing, and R. R. Miller, Rev. Sci. Instr. 34, 1456 (1963)].
11.A. A. Rudnitskii and I. I. Tyurin, J. Inorg. Chem. (USSR) 1, 207 (1956) (English transl.).
12.R. E. Bedford, NRC Rept. No. 7930 (1964).
13.C. R. Barber, Proc. Phys. Soc. (London) B63, 492 (1950).
14.H. Shenker, J. I. Lauritzen, R. J. Corruccini, and S. T. Lonberger, Natl. Bur. Std. Circular 561 (1955).
15.The rate of change with temperature of the thermoelectric potential difference of a thermocouple, is given several designations in current literature. In our case, where we are dealing with the materials Pt‐40Rh and Pt‐20Rh, the most appropriate (and preferred) term for is de/dt the Seebeck coefficient of Pt‐40Rh relative to Pt‐20Rh (or the relative Seebeck coefficient of Pt‐40Rh against Pt‐20Rh); this in turn is equal to the difference between the absolute Seebeck coefficients of Pt‐40Rh and Pt‐20Rh. Frequently, however, the term Seebeck coefficient is replaced by thermoelectric power, and de/dt becomes the thermoelectric power of Pt‐40Rh relative to Pt‐20Rh, or simply the thermoelectric power of the thermocouple Pt‐40Rh/ Pt‐20Rh. The synonymous term sensitivity of the thermocouple Pt‐40Rh/Pt‐20Rh is also commonly used. In this paper we denote de/dt by either thermoelectric power or sensitivity.
16.Detailed versions of these tables with entries given at 1 °C and 0.005 mV intervals of the arguments, respectively, are available as APH Rept. No. 1292.
17.W. Heyne, Exptl. Tech. Physik 12, 87 (1964).
18.As in the similar study of 20/5, we must point out that because of the method of monitoring the emf change (wire method at the palladium point) simple additivity of the time increments in Fig. 5 may not be quite valid. Each palladium calibration consumed some of the wire; the legs of the thermocouples were reduced in length by from 5 to 10 cm during these stability tests.
19.We remark that Aa2 produces the somewhat anomalous results here, and that lot Aa gave the least reproducibility between thermocouples (Aa2 being lower than Aa1). It is quite possible that Aa2 is not a typical thermocouple of lot Aa.
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