Pneumotachograph, Fleisch type
Accession #: 2008018
Description: with heating cable and metal screen diffuser/filter located in the rubber conical connector. The calibration label indicates that 1, 5 and 10 mm water pressure differential are generated for 1.5, 7.5 and 14.19 L/second air flow.
This device is inserted into a pipe in order to measure the flow within it. An assembly of axially orientated narrow tubes is placed in the gas flow. The device is designed with sufficient tubes to maintain laminar flow throughout the dynamic range of the sensor. Two outflow tubes emerging from the side of the pneumotachograph head, are exposed to the pressure of gas either side of the laminar flow assembly. The pressure across these two outlets is directly proportional to the flow passing through the head. It is sensed by connection to a sensitive differential pressure aneroid manometer. In clinical use, pneumotachographs of this type tend to suffer condensation that interferes with the accuracy of the reading so a heater is incorporated. The heater cable is shown bearing a calibration label for the sensor. This kind of pneumotachograph is called a Fleisch. An altrnative, Lilly pneumotachograph uses a large disc of fine mesh as the sensor. Its flow inlet and outlet are conical and permit the gas velocity to be minimised as it passes through the mesh and thus retains a laminar flow charactristsic.
This particular device is mre sophisticated than would normally be tolerated in clinical practice and its use is therefore confined to the laboratory.