Air Flow Meter Research Articles

Dynamic Detection on Airflow for Vehicle Intake System Based-on Hot-Film Anemometry Sensors

The goal of this study is to develop an airflow meter sensor for vehicle intake system detection in internal combustion engines. The study uses micro-electromechanical process technology to develop a hot-film flow meter with an alumina substrate and platinum film heater; the hotline method is used to create a micro airflow anemometry meter sensor relying on variations in resistance of the platinum film corresponding to different wind velocity at the set temperatures. The micro-sensor is less bulky and simpler structure than ordinary meters, and its small size enables it to provide good sensitivity and measurement precision. The alumina plate used in this study is produced by polishing an alumina substrate, a platinum film is then deposited on the plate to complete the micro-heater used in the sensor. Resistance on the sensor side varies as gas flows through the sensor, and the instrument determines airflow velocity on the basis of the changes in resistance caused by gas flow differences. Airflow velocity form 10 m/s to 60 m/s are used to test. Resistance displays a regular slope, indicating the relationship between airflow velocities varies remain predictable throughout the sensing range. Therefore, the sensor can achieve its airflow measurement purpose completely.

Imaging based optofluidic air flow meter with polymer interferometers defined by soft lithography

We present an optofluidic chip with integrated polymer interferometers for measuring both the microfluidic air pressure and flow rate. The chip contains a microfluidic circuit and optical cavities on a polymer which was defined by soft lithography. The pressure can be read out by imaging the interference patterns of the cavities. The air flow rate was then calculated from the differential pressure across a microfluidic Venturi circuit. Air flow rate measurement in the range of 0-2mg/second was demonstrated. This device provides a simple and versatile way for in situ measuring the microscale air pressure and flow on chip.

Non-invasive determination of instantaneous brachial blood flow using the oscillometric method

The oscillometric method has been widely used to measure arterial systolic and diastolic blood pressures, but its potential for arterial blood flow measurements still remains to be explored. The aim of this study was to non-invasively determine arterial blood flow using an oscillometric blood flow measurement system. The system consists of a pneumatic elastic cuff, an air-pumping motor, a releaser valve, a pressure transducer, and an airflow meter. To build a non-linear cuff model, we measured airflow pumped into the pneumatic cuff and cuff pressure using an airflow meter and pressure transducer during the inflation period, respectively. During the deflation period, only the pressure transducer was used to record cuff pressure. Based on the cuff model, the oscillometric blood flow waveform was obtained by integrating the oscillometric pressure waveform. We compared arterial blood flow derived from the maximum amplitude of the oscillometric blood flow waveform with Doppler-measured blood flow calculated with the diameters and blood velocities of the brachial arteries in 32 subjects who underwent diagnostic evaluations for peripheral arterial embolism. A linear correlation coefficient of r = 0.716 was found between the oscillometry- and Doppler-based blood flow measurements in the 32 subjects. These results suggest that blood flow passing through the brachial artery can be quantified non-invasively using the oscillometric approach after appropriate calibration.

Air and oxygen flowmeter confusion

We wish to report an episode of air being administered to a critically ill patient rather than oxygen, due to a mix-up with wall-mounted flowmeters. An elderly gentleman in ventricular tachycardia was anaesthetized in a resuscitation area for emergency cardioversion. Afterwards, what was thought to be high flow oxygen was administered via facemask. Mild hypoxaemia (paO2 ~8kPa) persisted, but the cause was unclear until it was noticed that the mask tubing was connected to a piped air flowmeter. Once this was corrected, hypoxaemia improved and the patient suffered no adverse consequences. While there are standards for the design and colour of gas cylinders and pipeline outlets, there are none for flowmeters.1 In this case the error was caused by the anaesthetist (new to the hospital that week) viewing the flowmeter from the side ( Figure 1a) with another mask dangling from above obscuring the label (Figures 1b and c). Figure 1 (A) and (B) Two flowmeters in the resuscitation room: masks are dangling down and obscuring the flowmeter below. (C) When the mask is moved away, the ‘Air’ label becomes obvious The use of non-interchangeable connectors for anaesthetic gases has reduced the potential for administering the wrong gas, but mistakes like this are clearly happening frequently enough for the UK National Patient Safety Agency to issue guidance on the matter.2 They suggested potential solutions including capping air flowmeters, clearer labelling, and that air flowmeters should only be attached when required. Even they recognized that these are weak barriers based on human or administrative actions, which would be inadequate for the safe delivery of other drugs.3 The universal outlets of oxygen and air flowmeters – whether attached to pipeline supplies in hospitals or cylinders in surgeries and ambulances – both accept oxygen mask tubing, and while this persists we believe that this error will be made repeatedly, potentially to the detriment of many patients.

A New Oscillometry-Based Method for Estimating the Brachial Arterial Compliance Under Loaded Conditions

We propose a new method for assessing the compliance of a compressed brachial artery using an oscillometry-based approach that is mathematically based on artery and air-cuff models. The cuff dynamics during the inflation period were characterized by simultaneously recording the cuff volume and internal pressure with a pressure transducer and an airflow meter, respectively, which yielded the envelope of the oscillation amplitudes (OAs) in the air cuff. This allowed the change in the arterial volume during each heartbeat at different cuff pressures to be calculated, yielding a changed volume-pressure curve. The oscillometry-derived loaded compliance of the brachial artery (Cosci) can be determined as the dynamic changed volume divided by the pulse pressure. Furthermore, we developed a direct scheme to calibrate the calculated dynamic changed volume. In addition, the proposed C(osci) was validated by comparing it with the compliance of the brachial artery (Cecho) estimated echocardiographically from the brachial arterial blood flow in 32 patients whose lower limbs exhibited numbness or lack of strength. The results showed that Cosci and Cecho were significantly correlated between the cuff pressures levels and the mean arterial pressure, systolic pressure, and diastolic pressure (r=0.616, 0.571, and 0.666, respectively; p<0.0001). This suggests that a useful measure of the loaded compliance can be derived from the pattern of the OA waveform in addition to oscillometry-based blood pressure measurements.

Ultrasonic Airflow Meter in Greenhouse Using Acoustic Reflection against Wall

In this paper, we described an ultrasonic airflow meter in a greenhouse using an acoustic reflection against a wall. The ultrasonic airflow meter is available for measuring the spatial mean wind velocity and direction, which consists of two sound probes and the wall of the greenhouse. Use of sound probes has advantage that the airflow accumulated along sound paths from a loudspeaker to a microphone is obtained in contrast to point measurements. The wind velocity and direction are calculated from time of flights (TOFs) of direct and reflected signals. The wind velocity and direction were measured in a greenhouse of 7.2 m × 29.0 m under factitious winds generated from two large electric fans located at the one side of the greenhouse. In addition, we detected air convection generated from two pairs of fans. These were measured every 20 seconds for 120 minutes. Regarding the measurement; by the proposed airflow meter and a reference; by a conventional one, their mean wind velocities were 0.12 and 0.15 (m/s), respectively. The presented airflow meter using the acoustic reflection against the wall is convenient to measure the wind velocity and direction in large‐size facilities such as the greenhouse.

A Novel Approach to Modeling and Simulation of NTC Thick-Film Segmented Thermistors for Sensor Applications

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper describes the design, modeling, simulation, and fabrication of thick-film segmented thermistors. These thermistors were printed on alumina using negative temperature coefficient 3K3 paste, composed of nanometer powder. Their room temperature resistance was measured versus the number of segments and electrode surface value for the fixed layer thickness and electrode spacing. After that, very large thermistors were printed to serve as both the powerful self-heaters and the heat loss sensors in the thermistor volume air flow meter and anemometer. For an application in AC bridges, impedance Z(f) and insertion loss S21 [dB] of the same largest segmented thermistor were measured using network analyzer HP8752A. Impedance modeling was performed using simple equivalent electrical circuit with circuit parameters estimated by fitting procedure (traditional approach), as well as using a commercial electromagnetic simulation program microwave office (MWO, novel approach). This was followed by the modeling of electrical current distribution over a number of segments done within the MWO. The results obtained from simulations and measurements were mutually compared. </para>

Decrease in functional residual capacity and ventilation homogeneity after neuromuscular blockade in anesthetized preschool children in the lateral position1

While functional residual capacity (FRC) is reduced in children undergoing general anesthesia, the lateral position leads to an increase in FRC compared with the supine position. The impact of neuromuscular blockade remains unknown. We tested the hypothesis that neuromuscular blockade leads to a decrease in FRC and increase in lung clearance index (LCI) while the application of positive endexpiratory pressure (PEEP) of 6 cmH(2)O leads to a restoration in both parameters. After approval of the local Ethics Committee, we studied 18 preschool children (2-6 years) without cardiopulmonary disease, who were scheduled for elective surgery. Anesthesia was standardized using propofol and fentanyl. FRC and LCI were calculated by a blinded observer using a SF6 multibreath washout technique with an ultrasonic transit-time airflow meter (Exhalyzer D). Measurements were taken in the left lateral position (PEEP 3 cmH2O) after 1. intubation with a cuffed tracheal tube, 2. neuromuscular blockade with rocuronium, and 3. the additional application of PEEP (6 cmH2O). Functional residual capacity mean (sd) decreased from 31.6 (4.4) ml.kg(-1) to 27.6 (4.2) ml.kg(-1) (P<0.001) following neuromuscular blockade while the LCI increased from 6.54 (0.6) to 7.0 (0.6) (P<or=0.001). After the application of PEEP (6 cmH2O), FRC increased to 32.4 (5.0) ml.kg(-1) whereas the LCI decreased to 6.58 (0.5) showing no significant changes from baseline measurements. In the lateral position, neuromuscular blockade led to a significant decrease in FRC associated with a small increase in ventilation inhomogeneity. FRC and LCI were restored to baseline levels with the application of PEEP 3 cmH2O that is in addition to a background of PEEP 3 cmH2O giving a total of 6 cmH2O PEEP.

An on-line optimisation of a SBR cycle for carbon and nitrogen removal based on on-line pH and OUR: the role of dissolved oxygen control

A pilot plant sequencing batch reactor (SBR) was applied in a wastewater treatment plant treating urban wastewater focused on carbon and nitrogen removal. From an initial predefined step-feed cycle definition, the evolution of the on-line monitored pH and calculated oxygen uptake rate (OUR) were analysed in terms of knowledge extraction. First, the aerobic phases of the SBR cycle were operated using an On/Off dissolved oxygen (DO) control strategy that concluded with a sinusoidal pH profile that made detecting the "ammonia valley" difficult. After changing to fuzzy logic control of the dissolved oxygen and by adding an air flow meter to the pilot plant, the pH evolution and on-line calculated OUR showed a clearer trend during the aerobic phases. Finally, a proposed algorithm for adjusting the aerobic phases of the SBR for carbon and ammonia removal is presented and discussed.

マイクロヒータの信頼性評価と車載用センサへの応用

A heat resistant micro heater consisting of a Pt thin film and a diaphragm was developed for automotive sensors and its reliability was evaluated from the mechanical and thermal points of view. The dominant failure modes for instant overheating and longtime heating were found to be de-lamination of the Pt film and electromigration of Pt, respectively. The life time was estimated to be over 10 years when the average heater temperature was 400°C (the peak temperature was over 600°C). As automotive sensors utilized this micro heater, the developed air flow meter and air quality sensor are described with features and evaluation methods unique to these sensors.

Continuous air rate measurement in flotation cells: a step towards gas distribution management

The distribution (profile) of air to a bank of cells has been shown to influence metallurgy. To facilitate setting a profile a sensor giving a continuous airflow rate signal is introduced. The principle of operation is collection of bubbles in a tube and measurement of pressure drop across a calibrated orifice as the air expels under steady state conditions. Experience with the unit is illustrated, from identifying a malfunctioning airflow meter, to revealing interaction between cells, and demonstrating the ease in establishing a profile down a bank of 16 cells with a multi-sensor unit.

Simultaneous real-time measurements of mastication, swallowing, nasal airflow, and aroma release.

Mastication, swallowing, breath flow, and aroma release were measured simultaneously in vivo using electromyography, electroglottography, a turbine air flow meter, and the MS-Nose, respectively. Signals were synchronized either electronically or by aligning the nasal airflow data with the breath by breath release of acetone. Chewing affected nasal airflow, with the flow fluctuations following the mastication pattern. Data analysis suggested that air was pumped out of the mouth into the throat with each chew, and the mean volume was 26 mL. Aroma release was associated with the pulses of air pumped from the mouth with each chew. During swallowing, there was no nasal airflow, but after swallowing, aroma release was evident. The volume of the retronasal route was estimated at 48 mL when swallowing and 72 mL when samples were chewed. The combination of techniques shows the effects of physiological processes on aroma release.

Apnea.

Apnea.

Application of an array sensor based on plasma-deposited organic film coated quartz crystal resonators to monitoring indoor volatile compounds

The basic response ability of an array sensor based on plasma-deposited organic film-coated quartz crystal resonators (QCRs) was investigated with a view to their use for indoor air monitoring. The array of plasma-deposited organic film-coated QCRs was applied to detect and separate volatile organic compounds (VOCs) including alkanes, aromatic carbons, chlorocarbons, ketones, and alcohols. Continuous monitoring tests were tried in a real room environment (a refreshment area and a smoking area) with an array of plasma-deposited organic film-coated QCRs along with commercial sensors for indoor monitoring, a relative humidity/temperature sensor, a carbon dioxide sensor, and a three-dimensional micro-ultrasonic airflow meter. To provide a comparison commercial VOC detectors based on a photo-ionization detector and a semiconductor for indoor monitoring tests were used. The plasma-deposited organic film-coated QCRs exhibited fast pulse responses to volatile compounds in the room air along the baseline shift correlated with relative humidity changes and more sensitive responses compared with commercial organic gas detectors.

Low-cost thermal Σ-Δ air flow sensor

This paper describes the design and optimization of a hot-wire air flowmeter. A low-cost design of the packaging allows good thermal contact with the airflow, as well as good thermal isolation between the hot and cold points. It is a compact solution which allows easy PCB mounting and adaptation to standard-size small air pipes. The design has been optimized for low-cost applications. The sensor is read out by a thermal sigma-delta modulator. The dynamic range of this modulator has been extended by adding a constant power offset to its output. The fractal nature of the modulator response at low-clock frequencies is also experimentally shown.

The Possibility and Importance of Increasing the Accuracy of Constricting Devices for Gases Taking into Account Experience in Investigating a Flowmeter with a Swivel Plate

The results of calibration tests on an air flowmeter instrument with a swivel plate are described. A flowmeter with changeable critical nozzles, calibrated on a test weight flowmeter instrument for gases, is used as the standard means of measurement.

Accuracy and consistency of respiratory inductive plethysmography for overnight tidal volume measurement.

To validate the accuracy and consistency of respiratory inductive plethysmography (RIP) in measuring tidal volume after an overnight sleep, tidal volumes of 18 patients with suspected sleep-disordered breathing and 8 normal volunteers were measured simultaneously with RIP (VTRIP) and with an ultrasonic airflow meter (VTUFM) before and after an unstrained overnight sleep on supine and lateral decubitus. The bias of the VTRIP was expressed as (VTRIP-VTUFM)/ VTUFM.100%, limits of agreement between VTRIP and VTUFM was measured by averaged bias +/- 2 s. Results showed that in normal subjects, the bias of RIP before and after overnight sleep was precise and consistent in both supine (0.7% and -1.6%) and lateral decubitus (3.7% and -0.56%). In these patients, the bias of RIP before and after sleep in supine also remained small (1.9% and 1.7%), but it became larger in lateral decubitus (24.5% and 20.4%) and 11.5% exceeded the limits of agreement observed in the evening. The patients' body mass indices (BMI) were higher than those of normal subjects (median 34.2 vs. 27.8 kg/m2). Pooled data showed that the bias of VTRIP in the morning on lateral decubitus but not on supine was correlated to BMI (Spearman R = 0.32, n = 52, P = 0.02). Thus, we were led to conclude that the accuracy of VTRIP overnight was precise and consistent in normal subjects, but the deviation of VTRIP measured on lateral decubitus in patients especially in those with excessive obesity was greater, thus, the method should not be used for quantitative determination.

A moment-of-momentum flux mass air flow measurement device

A unique air flow rate measurement device has been developed and tested foruse in the Axial Fan Research and Development facility at Michigan StateUniversity. The subject mass air flow meter is located downstream of a widevariety of test fan and component geometries. These can significantly changethe velocity profile entering the metering nozzles. For this reason a pointmeasurement of a characteristic velocity in the nozzle outlet would notprovide a viable experimental technique for the flow rate evaluation. Thisalso negates the option of using a simple nozzle discharge coefficient.An integral measurement technique was therefore implemented. A 90° turningpassage supported on a knife edge pivot was used to create a measurable netmoment-of-momentum flux. The resistive moment provided by a strain gauge forcetransducer was used to infer this net flux. The acceleration of the flow frominlet to outlet of the 90° turn and the larger contribution of theoutlet moment-of-momentum flux provide the desired insensitivity to thenon-uniform inlet flow conditions. A calibrated nozzle was used to determinethe `force-mass flow rate' transfer function.

Methods to calibrate a critical nozzle and flowmeter using reference critical nozzles

Methods to calibrate a critical nozzle and a flowmeter against reference critical nozzles are developed to replace the time-consuming conventional procedures. The discharge coefficient of a critical nozzle at a low Reynolds number was measured in a series connection with a reference nozzle in the upstream position, and its Reynolds number dependence was obtained by changing the reference nozzle. The dependence of similar critical nozzles with negligible machining error measured at low pressures using the series connections and at atmospheric pressure using a constant volume tank system coincide within ±0.04%. The same configuration was employed to measure the stability of the choking flow rate, which revealed premature unchoking phenomenon. The discharge coefficient of a critical nozzle under a reference condition was measured by a combination of three series connections with two reference critical nozzles at the upstream positions. Reynolds number dependence of a critical nozzle was measured using a combination of three series connections with four reference critical nozzles. These two methods require only one pressure gauge whose sensitivity is constant in a narrow range. An air flowmeter was calibrated at various volumetric flow rates against only one critical nozzle by controlling the upstream pressure of the nozzle.

Reduction of Measurement Error in Hot Wire Air Flow Meter due to Heat Conduction Loss through Probe Supports.

Reduction of Measurement Error in Hot Wire Air Flow Meter due to Heat Conduction Loss through Probe Supports.