Thermal, Flow Measuring Device with Diagnostic Function

Thermal flow measuring device (1), especially for determining and/or monitoring the mass flow (ΦM) and/or the flow velocity (vF) of a flowable medium (3) through a pipeline (2), comprising at least three sensor elements (4a,4b,4c) and an electronics unit (9), wherein each of the at least three sensor elements (4a,4b,4c) is at least partially and/or at times in thermal contact with the medium (3), and includes a heatable temperature sensor (5a,5b,5c), and wherein the electronics unit (9) is embodied to heat each of the three sensor elements (4a,4b,4c) with a heating power (P1,P2,P3), to register their temperatures (T1,T2,T3), to heat at least two of the at least three sensor elements (4a,4b,4c) simultaneously, to ascertain the mass flow (ΦM) and/or the flow velocity (vF) of the medium (3), from a pairwise comparison of the temperatures (T1,T2,T3) and/or heating powers (P1,P2,P3) of the at least three sensor elements (4a,4b,4c) and/or at least one variable derived from at least one of the temperatures (T1,T2,T3) and/or heating powers (P1,P2,P3), to provide information concerning a change of the thermal resistance of at least one of the at least three sensor elements (4a,4b,4c), from a response to an abrupt change ΔP of the heating power supplied to at least one of the at least three sensor elements, to provide information concerning a change of the inner thermal resistance of the at least one sensor element, and in the case that a change of the inner and/or outer thermal resistance occurs in the case of at least one of the at least three sensor elements (4a,4b,4c), to perform a correction of the measured value for the mass flow (ΦM) and/or the flow velocity (vF) and/or to generate and to output a report concerning the state of the at least one sensor element mass flow (ΦM) and/or the flow velocity (vF).