Labs Idea #13: Spirometer
A spirometer is used for lung function testing. The exhaled air volume is plotted against time to identify lung diseases such as COPD, asthma and others. It is a simple, quick, and painless way to check lungs and airways. Traditional analog sensing technologies with paddle wheels or turbines could be substituted by digital low cost sensing technologies, whithout sacrificing accuracy specifications. To meet accuracy requirements Sensirion's thermal flow sensor calibrated for differential pressure provides an attractive solution at lower cost than many ultrasonic sensors.
Sensirion's differential pressure sensor is a semiconductor MEMS version of the traditional hot wire anemometer. The sensing principle is based on thermal conductivity of the gas flowing over the sensor surface (Figure 1).
As opposed to diaphragm based differential pressure sensors, Sensirion's CMOSens differential pressure sensor characteristic shows high sensitivity especially at low differential pressures (Figure 2). This allows to reliably measure ultra-low flows or differential pressures.
To measure the exhaled air flow the differential pressure sensor was attached to a spirometer tube in bypass configuration (Figure 3).
For easy cleaning of the flow tube this spirometer design study using Sensirion's SDP3x differential pressure sensor is detachable from the spirometer tube (Figure 4).
The measurement results demonstrate that Sensirion's differential pressure sensor can be used as a flow sensor in spirometers due to its high sensitivity even at lowest flows (Figure 5).
- Sensirion's SDP3x differential pressure sensor in bypass configuration proves to be highly sensitive for pulmonary function testing.
- Sensor is detachable from the flow tube housing, making the spirometer body fully washable.