Ultrasonic flow meter with temperature compensation

摘要

The Invention provides a flow meter for measuring a liquid flow rate (V'). The flow meter Includes a well-known ultrasound measurement arrangement (UMA) including two piezoelectric ultrasound transducers (PT1, PT2), and a processor (P) eledrically connected thereto. The processor (P) is in a traditional manner arranged to measure a flow rate (V') based on ultrasonic measurement(s) of transit time difference(s) using the piezoelectric ultrasound transducers (PT1, PT2). In preferred embodiments, the processor (P) is further arranged to correct the measured flow rate (V') for an influence of a temperature (T) of the liquid in the measurement pipe. A measure of the temperature (T) of the liquid is based on a measurement of electrical capacitance, or at least measurement data related to the electrical capacitance of at least one of the two piezoelectric ultrasound transducers (PT1), thus utilizing the temperature dependence of electrical capacitance of the piezoelectric transducer element (PT1). The electrical measurement signal applied to the at least one transducer (PT1) may be a separate dedicated signal, or the temperature (T) may be derived from an electrical response to the electrical signal applied to the at least one transducer (PT1) for determining the ultrasonic transit time difference. The flow meter is capable of providing a high precision flow rate measurement over a wide range of flow rates and temperatures, and still the flow meter is simple and economical to manufacture since the temperature correction is performed without the need for a separate temperature sensor. The flow meter is suited for use in connection with a heat meter, e.g. in embodiments where the flow meter is arranged to transmit data related to the liquid temperature (T) to a heat calculation unit of the heat meter.