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Stop that interference! [Basic metrology].

Kibble, B*; Robinson, I A (2014) Stop that interference! [Basic metrology]. IEEE Instrum. Meas. Mag., 17 (4). pp. 37-38.

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The esoteric world of setting up and propagating the base SI units with measurements made by relatively simple apparatus to incredible parts-in-a-billion accuracy seems remote and irrelevant to ordinary everyday measurement and control, but the measurements rely on strict adherence to simple basic principles which are relevant right down the measurement chain. For example, many years ago one of us had to set up, maintain and disseminate the SI impedance units, the Farad, Henry and Ohm. This involved learning about the, then new, technique of coaxial measuring circuits as applied to the 1 to 10 kHz frequency range, and their simplicity and beauty was impressive. In these coaxial circuits the terminals of standard capacitors, inductors and resistors are no longer single-conductor binding-posts. They are now coaxial cable sockets and each socket constitutes associated pair of terminals. The inner pin of a socket replaces a binding-post and the screen of the sockets and the interconnecting coaxial cables is continuous with complete conducting screens in which standards are now enclosed. Measures are taken to ensure that whatever current flows through a standard and the inner conductor of each cable, an equal and opposite current flows back through the outer shields. The network of shields should be extended between the primary and secondary windings of instrument supply transformers. Unfortunately this is seldom, if ever, correctly done in commercial instruments and the isolation afforded by the shielding is compromised.

Item Type: Article
Subjects: Electromagnetics
Electromagnetics > Electrical Measurement
Identification number/DOI: 10.1109/MIM.2014.6873730
Last Modified: 02 Feb 2018 13:13
URI: http://eprintspublications.npl.co.uk/id/eprint/6292

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