INTRODUCTION

All fluid meters consist of two distinct parts, each of which has different functions to perform. The first part is the primary element, which is in contact with the fluid, resulting in some form of interaction. The second part or the secondary element usually translates the interaction between fluid and primary elements into a digital readout, a chart recording or an electrical signal which can be computed into engineering units such as volume, weight, or rate of flow.

Flow meters may be classified in two very general divisions: positive displacement meters and inferential meters. Inferential meters refer to those primary elements through which the fluid passes in a continuous stream. The flowing velocity and/or quantity of flow is, obtained from the interactions of the fluid stream and the primary elements by known physical laws supplemented by empirical relations. This section is devoted primarily to inferential meters. Positive displacement meters refer to those primary elements through which the fluid passes in successive and isolated quantities by alternately filling and emptying measuring chambers of known volume. Positive displacement meters are covered in Gas Measurement Manual, Part 2.