Flow meters perform different tasks in conditioning systems for gas analysis. The typically quite complex applications require the use of particularly corrosion-resistant materials and high operating reliability. In addition to visual flow measurements, they are also suitable for determining the depletion of the filtration capacity of the filter installed in the conditioning line. Electric limit switches can be mounted to the measuring tube for this purpose. These connect to the control system via suitable switch amplifiers. Types with built-in needle valve further allow for setting a specific flow rate.