Influence of the length of lead lines on the response of a variable orifice meter: analysis of sensitivity and settling time

Gas flow measurements are pivotal in several medical applications. For instance, mechanical ventilators and applications for respiratory monitoring need flowmeters with strict requirements: they must be accurate, with adequate dynamic response, high sensitivity (especially if used for neonatal purposes), and they must be almost insensitive to the composition of the gas Only few types of flowmeters are may be used in these applications. Among differential pressure flowmeters, characterized by good static and dynamic responses, variable area orifice meters (VAOMs) are gaining large acceptance in applications related to respiratory monitoring, estimation of respiratory function, and mechanical ventilation. VAOMs consist of two main parts: a primary element (basically a restriction), and a secondary element (i.e., a differential pressure transducer). The installation of the primary and the secondary elements can strongly influence the input-output relationship of VAOMs and can introduce relevant bias error. The aim of this study was twofold: i) the experimental assessment of the influence of the lead lines length (LL) on the calibration curve of a variable orifice meter; ii) the experimental analysis of the influence of LL on the step response of the flowmeter in terms of settling time. Results show that the value of LL influences both the static response and the step response: regarding the static response, the sensor sensitivity significantly decreases with LL (e.g., the sensitivity decreases from 5.3 Pa/L·min-1 to 4.0 Pa/L·min-1, when LL increases from 4 cm to 182 cm); concerning the step response, the flowmeter increases the settling time from approximately 20 ms up to 60 ms using LL values of 4 cm and 182 cm, respectively. The findings of this study can be useful to figure out the impact of the LL value on the sensor response; in addition may provide useful information to correct the sensor response if it is used in condition of installation different from the one used during the calibration.

[1]  Sergio Silvestri,et al.  A high sensitivity fiber optic macro-bend based gas flow rate transducer for low flow rates: theory, working principle, and static calibration. , 2013, The Review of scientific instruments.

[2]  G. Bellon,et al.  Infant respiratory function testing , 1997 .

[3]  Huibert Burger,et al.  Correction factors for oxygen and flow-rate effects on neonatal Fleisch and Lilly pneumotachometers , 2003, Pediatric critical care medicine : a journal of the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies.

[4]  Emiliano Schena,et al.  Flow measurement in mechanical ventilation: a review. , 2015, Medical engineering & physics.

[5]  Sergio Silvestri,et al.  Temperature influence on the response at low airflow of a variable orifice flowmeter , 2017, 2017 39th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC).

[6]  Sergio Silvestri,et al.  A novel target-type low pressure drop bidirectional optoelectronic air flow sensor for infant artificial ventilation: measurement principle and static calibration. , 2011, The Review of scientific instruments.

[7]  E. Iso,et al.  Measurement Uncertainty and Probability: Guide to the Expression of Uncertainty in Measurement , 1995 .

[8]  Sergio Silvestri,et al.  An orifice meter for bidirectional air flow measurements: Influence of gas thermo-hygrometric content on static response and bidirectionality , 2013 .

[9]  Sergio Silvestri,et al.  Linearity dependence on oxygen fraction and gas temperature of a novel Fleisch pneumotachograph for neonatal ventilation at low flow rates , 2012 .

[10]  U. Frey,et al.  SERIES "STANDARDS FOR INFANT RESPIRATORY FUNCTION TESTING:ERJ/ATS TASK FORCE" Edited by J. Stocks and J. Gerritsen Number 1 in this series Specifications for equipment used for infant pulmonary function testing , .

[11]  David W. Kaczka,et al.  Four methods of measuring tidal volume during high-frequency oscillatory ventilation , 2006, Critical care medicine.

[12]  R. W. Miller,et al.  Flow Measurement Engineering Handbook , 1983 .

[13]  H. H. Bruun,et al.  Hot-Wire Anemometry: Principles and Signal Analysis , 1996 .

[14]  A.F.P. van Putten,et al.  A silicon bidirectional flow sensor for measuring respiratory flow , 1997, IEEE Transactions on Biomedical Engineering.

[15]  Stephen B. M. Beck,et al.  Experimental study of the pressure drop after fractal-shaped orifices in turbulent pipe flows , 2010 .

[16]  Sergio Silvestri,et al.  A transistor based air flow transducer for thermohygrometric control of neonatal ventilatory applications. , 2008, The Review of scientific instruments.

[17]  Richard Plavka,et al.  Expired tidal volumes measured by hot‐wire anemometer during high‐frequency oscillation in preterm infants , 2006, Pediatric pulmonology.

[18]  Halit Eren,et al.  Measurement, Instrumentation, and Sensors Handbook : Spatial, Mechanical, Thermal, and Radiation Measurement , 2014 .

[19]  Gerald L. Morrison,et al.  Comparison of orifice and slotted plate flowmeters , 1994 .

[20]  S. Turney,et al.  A mathematical model for the ultrasonic measurement of respiratory flow , 2006, Medical and biological engineering.

[21]  P D Sly,et al.  In vitro assessment of an ultrasonic flowmeter for use in ventilated infants. , 2000, The European respiratory journal.

[22]  A. Coates,et al.  A very low dead space pneumotachograph for ventilatory measurements in newborns. , 1990, Journal of applied physiology.

[23]  Emiliano Schena,et al.  Experimental Assessment of a Variable Orifice Flowmeter for Respiratory Monitoring , 2015, J. Sensors.