CPAP breathing machines device selection and design

CPAP or continuous positive airway pressure is a respiratory ventilation method, used primarily for home treatment of sleep apnea syndrome.

Pressure sensor, microprocessors and other devices in the respiratory equipment plays an important role. This article will explore the ventilator system device selection and related design.

CPAP or continuous positive airway pressure is a respiratory ventilation method, used primarily for home treatment of sleep apnea syndrome.

In sleep, the muscles relax, will usually be natural to narrow the cause of upper respiratory tract. This reduces the oxygen content in the blood and cause a wake up from sleep.

Pressure sensor in the respiratory equipment plays an important role, it is responsible for the physical values (for example, airway pressure and flow) converted to differential signal.

Air and oxygen flow sensor-generated signal can help microprocessor control motor, which adjust or maintain patient inspiratory and expiratory pressure required. Typically, these highly cost-effective non-linear sensors are large offset and offset drift, causing the signal exceeds or is lower than proportional to temperature change. Low offset voltage and smaller time and temperature drift of the amplifier is ideal for signal conditioning.

Through the three current phase of at least two phase and for motor driven bridge powered DC bus voltage monitor, you can actually control of DC motors.

On the phase current, there are two methods you can use: high-side or low-side. Direct phase measurement or high side approach requires high speed differential amplifier or current shunt monitor, this method is usually more accurate. Low-side measurement of close to half-bridge grounding and use the more simple amplifier, although less costly, but accuracy is also lower. DC motor driven by discrete FET. It is highly recommended that you use the TI drv series, it offers a thermal protection features integrated drive and bridges, and smaller with higher accuracy and efficiency.

The microprocessor is responsible for the implementation of several actions, including pressure signal sampling and calculation of the airway pressure and flow, in order to communicate with the motor.

To efficient real time completing these operations, the need for high-speed, low-power, highly integrated microprocessor. High-quality DSP can be used for such applications, also for patients with extremely quiet environment.

System block diagram

System block diagram

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