Four terminal-pair to anything else!

Before the impedance of a device can be measured properly it must first be defined by specifying appropriate electrical conditions at the terminals of the device where the conductors from the measuring instrument connect to it. It is then the business of the metrologist to ensure that these defining conditions, or ones equivalent to them, or ones which lead to a negligible or calculable change to the measurand are fulfilled by the measuring instrument. Instruments are now available which can measure impedances defined as four terminal-pair components at frequencies from a few tens of hertz to a few tens of megahertz over a very wide range of impedances from micro-ohms to many gigaohms. These instruments can be calibrated so that the measurements they make are accurate and traceable to the SI ohm. The purpose of this paper is to describe adapters which convert between a four terminal-pair definition and other simpler, and in some cases, incomplete, terminal definitions. The adapters make either a negligible or a small and measurable contribution to the total impedance being measured.