Abstract
The Type N thermocouple, at its introduction in the early 1980s, was intended to radically improve base-metal thermocouple measurements and would render other base-metal types obsolete, or so it was claimed. Almost 40 years on, Type K persists in being the thermocouple of choice, despite adequate opportunity for the uptake of Type N. The reasons for this may be many; however, recent research at is showing Type N, at least at low temperatures, is not nearly as stable as early claims made out. This study reports on the inhomogeneities in Type N thermoelements, which develop as a function of temperature and time in a selection of mineral-insulated-metal-sheath (MIMS) and bare-wire samples sourced from a range of manufacturers. Measurements were made using a linear-gradient furnace and high-resolution homogeneity scanner. It was found that Type N thermocouples, in both the bare-wire and MIMS format, are susceptible to significant deviations in Seebeck coefficient from the reference functions at temperatures between 100 °C and 950 °C. In fact, use at temperatures below 500 °C can result in measurement errors equal to or worse than for equivalently specified Type K. Consequently, the benefits of using as-supplied Type N, in terms of accuracy and longevity, are only fully realized at temperatures greater than 900 °C. Despite these findings, additional experiments revealed drift rates can be reduced by about a factor of four if thermal preconditioning between 600 °C and 900 °C is used on MIMS Type N, which is similar to the improvements seen for thermally preconditioned MIMS Type K.
Similar content being viewed by others
References
R.E. Bentley, Theory and Practice of Thermoelectric Thermometry, 1st edn. (Springer, New York, 1998)
R.D. Barnard, Thermoelectricity in Metals and Alloys (Taylor and Francis LTD, Milton Park, 1972)
D.D. Pollock, Thermocouples Theory and Properties (CRC Press, Boca Raton, 1991)
G.W. Burns, M.G. Scroger, G.F. Strouse, M.C. Croarkin and W.F. Guthrie, Temperature-electromotive Force Reference Functions and Tables for the Letter-designated Thermocouple Types Based on the ITS-90, (NIST, 1993)
N.A. Burley, R.M. Hess, C.F. Howie and J.A. Coleman, Temperature, its measurement and control in science and industry, vol. 5, part 2, ed. by J. F. Schooley, (Instrument Society of America, 1982), pp. 1159-–1166
F.S. Sibley, N.F. Spooner, B. Hall, Instrum. Technol. 15, 53–55 (1968)
A.W. Fenton, Temperature, its measurement and control in science and industry, vol. 4, part 3, ed. by H. H. Plumb, (Instrument Society of America, 1972), pp. 1973-1990
E.S. Webster, Int. J. Thermophys. 35, 574–595 (2014)
E.S. Webster, D.R. White, H. Edgar, Int. J. Thermophys. 36, 444–466 (2014)
E.S. Webster, Int. J. Thermophys. 38, 135 (2017)
T.G. Kollie, J.L. Horton, K.R. Carr, M.B. Herskovitz, C.A. Mossman, Rev. Sci. Instrum. 46, 1447–1461 (1975)
N.A. Burley, R.L. Powell, G.W. Burns and M.G. Scroger, The Nicrosil versus Nisil thermocouple: Properties and thermoelectric reference data, (NBS, 1978)
C.D. Starr, T.P. Wang, J. Testing Eval. 4, 42–56 (1976)
T.P. Wang, C.D. Starr, ASTM J. 8, 192–198 (1980)
T.P. Wang and C.D. Starr, Temperature, its Measurement and Control in Science and Industry, vol. 5, part 2, ed. by J. F. Schooley, (Instrument Society of America, 1982), pp. 1147–1157
R.E. Bentley, Temperature, its measurement and control in science and industry, vol. 6, part 1, ed. by J. F. Schooley, (Instrument Society of America, 1992), pp. 591–594
J.L. Horton, T.G. Kollie, L.G. Rubin, J. Appl. Phys. 48, 4666–4671 (1977)
N.A. Burley and J.L. Cocking, Temperature, its Measurement and Control in Science and Industry, vol. 5, part 2, ed. by J. F. Schooley, (Instrument Society of America, 1982), pp. 1129–1145
W.H. Christie, R.E. Eby, R.L. Anderson, T.G. Kollie, Appl. Surf. Sci. 3, 329–347 (1979)
R.L. Anderson, J.D. Lyons, T.G. Kollie, W.H. Christie and R. Eby, Temperature, its Measurement and Control in Science and Industry, vol. 5, part 2, ed. by J. F. Schooley, (Instrument Society of America, 1982), pp. 977–1007
R.E. Bentley, T.L. Morgan, J. Phys. E 19, 262–268 (1986)
R.E. Bentley, Temperature, its Measurement and Control in Science and Industry, vol. 6, part 1, ed. by J. F. Schooley, (Instrument Society of America, 1992), pp. 585–590
R.E. Bentley, J. Phys. E 20, 1368–1373 (1987)
E.S. Webster, D.R. White, Metrologia 52, 130–144 (2015)
N.A. Burley, Measurement 8, 36–41 (1990)
G. Coggiola, L. Crovini, A. Mangano, High Temp. High Press. 20, 419–432 (1988)
N.A. Burley, Temperature, its measurement and control in science and industry, vol. 4, part 3, ed. by H. H. Plumb, (Instrument Society of America, 1972), pp. 1677–1695
E.S. Webster, Int. J. Thermophys. 38, 5 (2016)
R.E. Bentley, G.F. Russell, Sens. Actuators A 16, 89–100 (1988)
A. Seeger, G. Schottky, D. Schumacher, Phys. Stat. Sol. 11, 363–370 (1965)
R.E. Bentley, J. Phys. D Appl. Phys. 22, 1902–1907 (1989)
R.E. Bentley, J. Phys. D 22, 1908–1915 (1989)
E.S. Webster, Int. J. Thermophys. 38, 70 (2017)
D.D. Pollock, Temperature, its measurement and control in science and industry, vol. 5, part 2, ed. by J. F. Schooley, (Instrument Society of America, 1982), pp. 1115–1120
Author information
Authors and Affiliations
Corresponding author
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
About this article
Cite this article
Webster, E. A Performance Assessment of Current Formulations of Bare-Wire and Mineral-Insulated-Metal-Sheathed Type N Thermocouples. Int J Thermophys 42, 83 (2021). https://doi.org/10.1007/s10765-021-02831-y
Received:
Accepted:
Published:
DOI: https://doi.org/10.1007/s10765-021-02831-y