Temperature influence on the response at low airflow of a variable orifice flowmeter

In mechanical ventilation, in particular when neonates are ventilated, it is crucial to accurately control the amount of the gas delivered to the patients. Mechanical ventilators are equipped with one of more flowmeters. The signal of the flowmeter is used as feedback to control the amount of gas delivered to the patients. Therefore, the accuracy of the flowmeter plays a crucial role in the accurate adjustment of the gas amount delivered by the ventilator. Among several solutions, variable area orifice meters (VAOMs) have several valuable features (e.g., good accuracy, and adequate frequency response), moreover they have the main advantage, with respect to orifice meters, related to the linearity of the response. Despite of their spread in this field, there are not studies focused on the analysis of the air temperature influence on VAOMs response. This study focuses on this topic by investigating the gas temperature influence on the response of a commercial VAOM. Experiments have been performed at low airflow (up to 1.5 L·min^-1) and at four different temperatures (i.e., from 22°C to 38°C) covering the range of interest in the field of artificial ventilation. Results show that the response of the VAOM under test is sensitive to temperature: at constant airflow the higher the temperature the higher the sensor output. This analysis may be useful to add correction to sensor output in order to reject the influence of temperature, so to minimize the measurement error due to this factor.