Instruments incorporating thermionic valves and their characteristics

In the first part of the paper the authors discuss the main valve characteristics which are of importance in instrument design, and describe types of valves specially designed for instrument purposes. The principles are outlined of the various types of valve instruments for the measurement of alternating voltages (including ¿slide-back,¿ peak, grid-leak, and anode-bend voltmeters), and of voltmeters and electrometers for direct voltages; and methods of measuring very small values of current and power are described. Reference is also made to other applications such as harmonic analysis, frequency measurement, and the measurement of physical quantities. The paper concludes with a brief comparison between valve-operated and other types of instrument and indicates possible future lines of development.