Identify one key characteristic of positive displacement flow meters.

Positive displacement flow meters are characterized by their method of operation, which involves capturing a fixed volume of fluid and then mechanically displacing it to measure flow. This design allows for accurate flow measurement regardless of the fluid's density, viscosity, or temperature, making positive displacement meters highly reliable for various applications.

In contrast, measuring flow using electromagnetic sensors involves a completely different mechanism, which is not applicable here. Relying on temperature variations pertains to specific types of flow meter technologies that utilize temperature to gauge flow, which again does not align with the defining feature of positive displacement. Similarly, the measurement of pressure and temperature simultaneously relates to other types of instruments designed to analyze fluid properties, rather than flow measurement specifically associated with positive displacement meters.