Keywords
AC bridge
balanced-ratiometric mesurement method
hybrid method
Abstract
The paper article describes the circuit of an automatic AC bridge for high precision temperature measurements using a standard platinum SPRT sensor. An original method for measuring the impedance parameters of SPRT sensor which allows to carry out the measurement process without loss of accuracy, is described in detail. This measurement method is proposed to name as hybrid method. It is a combination of a balanced method for rough compensation of the circuit and a ratiometric method which accurately measures the ratio of two values of the imbalance signal, before and after its known change. With this method, the measuring circuit also does not require a circuit to compensate for the reactive component of the SPRT sensor impedance. The inductive voltage divider with lower number of digits is needed only for the coarse compensation. This circuit is simpler and at lower cost of the hardware resources allows to achieve the same accuracy as the most accurate thermometric bridges with fully balanced circuits.
References
Report to the CIPM on the implications of changing the definition of the base unit kelvin. Prepared by the task group TG-SI of the CCT. J. Fisher (chairman), S. Gerasimov, K.D. Hill, at al. 02 May (2007) http://www.temperatures.ru/pdf/Kelvin_
CIPM.pdf
Hill J.J., Miller A.P., An A.C. Double bridge with inductively coupled ratio arms for platinum resistance thermometry. Proc. IEE, 110 (2), 453 (1963)
Gibbings D.L., An alternating current analogue of the Kelvin double bridge, Proc. IEE, 109C, 307 (1962)
Foord T.R., Langlands R.C., Binnie A.J., Transformer-ratio bridge network with precise lead compensation, Proc. IEE, 110 (9), p. 1693 – 1700 (1963)
Cutkosky R., An automatic resistance termometer bridge. IEEE Transactions on Instr. and Measur. IM – 29 (4), p. 330 – 333 (1980)
Knight R.B., Precision bridge for resistance thermometry using a single inductive current divider. Euromeas-77; Europe conference on precise electrical measurements, London, p. 132-134 (1977)
Grinevich F.B., Surdu M.N., High-precision variational measuring systems of alternating current, Kiev: Nauk. dumka, 192 p. (1989), (Rus.)
Tretiak I.V., Variational methods of correction of alternating current transformating bridge errors. Abstract of a thesis Ph.D, NAS of Ukraine, Institute of Electrodynamics. Kiev, 18 p. (1991) (Rus.)
Grinevich F.B., Surdu M.N., Mikhal A.A., Shvets T.V., Kromplias B.A., Meleshchuk D.V., Precision bridge of alternating current for operation in 125-925 Hz frequency range. Tekhnichna Elektrodynamika. Thematic issue “Problems of modern electrotechnics”, 3, 76–78 (2000) (Rus.)
Mikhal A.A., Warsza Z.L., Electromagnetic Protection in High Precision Tri-axial Thermometric AC Bridge., R. Szewczyk et al. (eds.), Progress in Automation, Robotics and Measuring Techniques, vol. 3, Measuring Techniques and Systems, Advances in Intelligent Systems and Computing 352, 147 -156 (2015) Springer International DOI: 10.1007/978-3-319-15835-8_17
Mikhal A.A., Warsza Z.L., Simple Methods to Measure the Additive Error and Integral Nonlinearity of Precision Thermometric Bridges., R. Szewczyk et al. (eds.), Progress in Automation, Robotics and Measuring Techniques, vol. 3, Measuring Techniques and Systems, Advances in Intelligent Systems and Computing 352, 157 -170 (2015) Springer International DOI: 10.1007/978-3-319-15835-8_18
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