一、Role of ventilator flow sensor
1.The principle of the ventilator is to use the pressure difference to form a breathing process. How to control this process, we should use our flow sensor, flow sensor used is a very long time, it will be used in the breathing machine, mainly will be inhaled and exhaled gas gathering into electrical signal, sent to the measuring data processing in the chip, the data is breathing volume, minute ventilation, ventilation rate, etc.
According to different ventilator function and design, the flow sensor readings provide not only show that control of the breathing machine, alarm, also plays a decisive role, such as flow sensor to measure the real value of feed to electronic control parts compared with the setting of the panel, using the servo valve to adjust the control error inhaled and exhaled gas flow; Signals generated by air and oxygen flow sensors at the front end of the inspiratory system help the microprocessor control the valve to provide the oxygen concentration required by the patient. The detection values of flow velocity and flow also directly affect the switching of expiratory and inspiratory phases, the alarm of the upper and lower limits of minute ventilation, the sensitivity of flow triggering, the real-time waveform of airflow and the monitoring display of P-V-ring, etc. The performance of flow sensor directly affects the accuracy and reliability of ventilator parameters.
二、Principle and application of ventilator flow sensors
Ultrasonic type flow sensor: the so-called ultrasonic wave refers to the frequency higher than 20kHz, the human ear can not hear the mechanical wave. It has good directionality, strong penetrating power, and will produce significant reflection when encountering magazine or object interface. When an ultrasonic wave propagates in a moving fluid, it carries information about the velocity of the fluid. These physical properties of the ultrasonic wave can be used to calculate the flow velocity of the fluid.
Ultrasonic sensors are divided into ultrasonic transmitter and ultrasonic receiver. The ultrasonic transmitter uses the inverse piezoelectric effect of piezoelectric materials, that is, when the ultrasonic electrical signal is applied to it, it will produce ultrasonic waves; The ultrasonic receiver makes use of the piezoelectric effect of piezoelectric materials, that is, when an external force is applied to the material, it produces a charge output. That is, the ultrasonic transmitter converts electrical energy into ultrasonic energy and sends it to the measured current body, and the ultrasonic receiver receives the ultrasonic signal and converts it into electrical signal output. According to the detection method, it can be divided into different types of ultrasonic sensors, such as propagation velocity acoustic time difference method, Doppler method, beam shift method, and noise method. At present, the ultrasonic flow sensors used in ventilators are mainly sound time difference method and Doppler method.