Positive displacement meters are devices used to measure the flow of liquids or gases by capturing a fixed volume of the substance and then counting how many times this volume is filled and emptied. This method ensures accurate measurements, making them ideal for applications where precision is crucial, such as in the oil and gas industry or water supply systems. These meters operate by using mechanical components, such as gears or pistons, that move in response to the flow. As the fluid passes through the meter, it displaces these components, allowing for a direct measurement of the volume. Common types include gear meters and diaphragm meters.