Abstract

An apparatus for verifying the calibration of a flow meter contains a flow sensor assembly which has a flow tube defining an axial fluid path through the flow sensor assembly; an upstream resistance thermometer in thermal contact with the flow tube; a downstream resistance thermometer in thermal contact with the flow tube, where the two thermometers are operationally connected to a means for producing an output in response to a difference between the heat flows from the first and second resistance thermometers; and means for asymmetrically transferring heat to the first and second resistance thermometers, independently of fluid flow through the flow tube. The calibration of the flow meter's thermal and electronic systems is verified by measuring the flow meter's output in response to a first asymmetric heat transfer, to the upstream and downstream resistance thermometers, when the flow meter is calibrated. The output of the flow meter in response to a second asymmetric transfer, to the upstream and downstream thermometers, is subsequently measured and comparison of the two readings verifies whether the flow meter's thermal and electronic systems remains calibrated.