Aerodromograaf, flow sensor, 1905

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An early bi-directional flow sensor.  From “Bijdrage tot de pharmacodynamica der respiratie.” By Evert van Kekem, Published by the University of Utrecht, 1905.

Two small plastic counterbalanced cups were suspended in a white spirit (alcohol?) bath (essentially small water-seal spirometers).  Small tubes (H, H’) lead to each of them from either side of a pitot tube.  Airflow through a pitot tube causes one side to rise and the other to fall.  Which cup rises and which cup falls depends on the direction of airflow.  The motion of the stylus (D) was roughly proportional to the flow rate.

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