COMPACT ULTRASONIC FLOWMETER WITH IMPROVED ANTENNA PERFORMANCE

An ultrasonic flow meter for measuring a flow rate of a fluid. The flow meter has a flow tube (FT), and a flow meter housing (H) associated with the flow tube (FT). A printed circuit board (PB) is arranged in the housing (H) and including a processor for controlling operations of the flow meter, a meter circuit, and a radio circuit for generating a radio signal with data indicative of a measured flow rate of the fluid. A lid (LD) may serve to close off the housing (H). An insert (I) in the housing(H) has a wall (W) and a bottom (B) forming a container (CD) for a desiccant. A front part (FP) serves as a lid for the container (CD) for the desiccant. An antenna element (AE) is mounted on a peripheral part (PP) of the insert (I) and being configured to radiate radio waves in response to the radio signal. The insert (I) has spacing elements (RB) on which the antenna element (AE) is mounted so that at least a minimum distance (D) to an inner part of a wall (W) of the container (CD) for the desiccant is provided, so as to reduce influence of at least one property of the desiccant on an impedance matching between the antenna element (AE) and the radio circuit. Hereby, with a distance (D) of such as 4-6 mm, it has been found to cause antenna performance to be generally independent of the desiccant, e.g. the position of the desiccant in the container (CD), thus causing the flow meter to have a stable radio communication with a high output which is independent on its orientation during operation. This further allows the flow meter to be suited for low-cost mass production.