With the widespread of COVID-19, ventilators have been becoming an important medical source. Inside a ventilator, there is a key component---Differential Pressure Sensor. Maybe we could use this sensor to build up our own ventilator.
To begin with, let’s get to know three common pressure sensors:
Absolute pressure sensor: This sensor measures the pressure relative to perfect vacuum.
Gauge pressure sensor: This sensor measures the pressure relative to atmospheric pressure.
Differential pressure sensor: This sensor measures the difference between two pressures, one connected to each side of the sensor.
Come from Pressure sensor - Wikipedia【https://en.wikipedia.org/wiki/Pressure_sensor】
1.Sample Code Test
Test the sample code, and the following results will be found on the serial monitor: Get Single Measurement Data
Get the Filtered Data
The data error of single measurement is very small, and the pressure difference between the two sides is very close to 0 Pa. After filtering, the data error can be further reduced.
2.Pressure Change Test (Use a syringe to change pressure)
For the sake of convenience, we defined the left nozzle of the sensor as the reference port, the right one as test port. The heat shrink tube will be always connected to the test port in the following tests.
1.Connect the test port with a syringe via a heat shrink tube.
The result will be displayed on the Arduino Serial Plotter. Blue is for temperature, red is for pressure. The measurement interval is 1ms.
The following image presents the temp & pressure change when the syringe is just connected to the test port.
The image below shows the temp & pressure change after the device is kept still for a while.
2. The reference port is exposed to air. Connect the test port with the syringe via a heat shrink tube. Push and pull the syringe continuously, at this time the data changed rapidly, so it can be seen that this sensor has pretty high sensitivity.
The following images show the two different test modes: 1. Push the syringe and then keep still 2. Pull the syringe and then keep still.
(Except for the factor of slightly hand tremor during operation, it can be roughly seen that the sensor can give very stable performance in measurement.)
3.Block the nozzle of reference port with your finger to simulate a certain pressure, and connect the test port with the syringe via a heat shrink tube.
Pull and push the syringe constantly. Then when releasing the syringe plunger, the curve went back to the position of 0pa(since the plunger went back to the original position). When once again, push or pull the syringe plunger for a certain distance, and then keep still, the pressure curve kept to a fixed value gradually.
Push the syringe plunger and then keep still.
Pull the syringe plunger and then keep still.
3.Sensor Readings Accuracy Test
Since I don’t have professional equipment, so I can only use the physical knowledge I learned in school to carry out this measurement: calculate the pressure that should be input to the sensor by the water height difference. Based on the gravity where I stay, 1mm of water height difference equals to 9.8Pa.
Data 1:
Sensor Average Reading vs Water Column Pressure Difference
Exchange the test port and reference port, and do the test again.
Data 2
From the above we can see that both nozzles of the sensor can be used as test port to measure negative pressure.
4.Conclusion
Due to the constrains of measurement tools, methods and environment, the above-mentioned measurement data error is only for reference (the actual error should not be so large). If you are interested, it would be appreciated that you could give your opinion about how to do this test in a better way. Or if possible, we would esteem it a great favour if you test this sensor with professional equipment.
