Saccomandi Paola, Schena Emiliano, Silvestri Sergio
Faculty of Biomedical Engineering, University Campus Bio-Medico, Rome, Italy.
Rev Sci Instrum. 2011 Feb;82(2):024301. doi: 10.1063/1.3549624.
An optoelectronic target-type volumetric air flow-rate transducer for bidirectional measurements is presented. The sensor is composed of a T-shaped target and two nominally identical LED-photodiode couples which are operated in differential mode. The sensitive surfaces of the photodiodes are differentially shadowed by the deflection of the target, which in turn depends on the gas flow-rate. The principle of operation is described in mathematical terms and the design parameters have been optimized in order to obtain the highest sensitivity along with minimal pressure drop and reduced dimensions. The sensor is placed in a 20 mm diameter hose and was tested with air flow-rate in the typical temperature range of mechanical ventilation between 20 and 40 °C. The theoretical model was validated through experiments carried out in the volumetric flow range from -7.0 to +7.0 l min(-1). The nonlinear behavior allows sensitivities equal to 0.6 V l(-1) min for flow rates ranging from -2.0 to +2.0 l min(-1), equal to 2.0 V l(-1) min for flow rates ranging from -3.0 to -2.0 l min(-1) and from +2.0 to +3.0 l min(-1), up to 5.7 V l(-1) min at higher flow rates ranging from -7.0 to -3.0 l min(-1) and from +3.0 to +7.0 l min(-1). The linear range extends from 3.0 to 7.0 l min(-1) with constant sensitivity equal to 5.7 V l(-1) min. The sensor is able to detect a flow-rate equal to 1.0 l min(-1) with a sensitivity of about 400 mV l(-1) min. The differential nature of the output minimizes the influence of the LEDs' power supply variations and allows to obtain a repeatability in the order of 3% of full scale output. The small pressure drop produced by the sensor placed in-line the fluid stream, of about 2.4 Pa at 7 l min(-1), corresponds to a negligible fluid dynamic resistance lower than 0.34 Pa l(-1) min.
本文介绍了一种用于双向测量的光电靶式体积流量传感器。该传感器由一个T形靶和两个名义上相同的LED - 光电二极管对组成，它们以差分模式工作。光电二极管的敏感表面因靶的偏转而产生差分阴影，而靶的偏转又取决于气体流量。文中用数学术语描述了其工作原理，并对设计参数进行了优化，以获得最高灵敏度，同时使压降最小且尺寸减小。该传感器放置在直径为20 mm的软管中，并在机械通气的典型温度范围20至40°C下，对空气流量进行了测试。通过在 - 7.0至 + 7.0 l min⁻¹的体积流量范围内进行实验，验证了理论模型。对于 - 2.0至 + 2.0 l min⁻¹的流量，非线性行为使得灵敏度等于0.6 V l⁻¹ min；对于 - 3.0至 - 2.0 l min⁻¹和 + 2.0至 + 3.0 l min⁻¹的流量，灵敏度等于2.0 V l⁻¹ min；对于 - 7.0至 - 3.0 l min⁻¹和 + 3.至 + 7.0 l min⁻¹的较高流量，灵敏度高达5.7 V l⁻¹ min。线性范围从3.0至7.0 l min⁻¹，恒定灵敏度等于5.7 V l⁻¹ min。该传感器能够检测到等于1.0 l min⁻¹的流量，灵敏度约为400 mV l⁻¹ min。输出的差分特性使LED电源变化的影响最小化，并允许获得满量程输出约3%的重复性。置于流体流中的传感器产生的小压降，在7 l min⁻¹时约为2.4 Pa，对应于低于0.34 Pa l⁻¹ min的可忽略不计的流体动态阻力。
