Inline Pressure Sensor
Inline Pressure Sensor for high pressure and alcohols
Authors: Bao Nguyen
Affiliations: Oregon State University and OPEnS Lab
Contact email: [email protected]
The first target when choosing a liquid media pressure sensor for the eDNA was being able to handle alcohol in high concentration. The second consideration is the pressure sensor casing (if there is one) would need to be easy to manufacture in the OpenSlab scale. The third consideration is the max pressure that the sensor read is above 15 PSI.
The first pressure sensor was suggested for the eDNA by the lab was the Non-Newtonian developed by Manuel and Luke. Detail about their publication can be found here. The design, use the MS5803-02BA SMD sensor that has up to 24 bits ADC which very accurate in eDNA concern. The pressure casing was printed out of resin, which also has a very high resolution for a watertight fit.
The major drawback of this Non-Newtonian pressure sensor module is the casing material itself. All the resin that is sold by Form-Lab, the SLA printer manufacturer, cannot handle alcohol for a long period of time. The structural integrity of the print will degrade, the part will get swollen up and soften. Different printing material was tried with FDM printer using ASA and nylon, but the quality is not enough for the watertight device under pressure. Moreover, the pressure sensor range of 4.35PSI ~ 15.95PSI is absolute. With 1.0 atm = 14.70 psi, the sensor is only useful to read up to 1.25 PSI gauge pressure in the tubing, below the function target for the eDNA (15PSI).
The alternative for pressure sensor in alcohol is Honeywell ABPDANT030PG0D3. From the specification sheet, the pressure sensor is rated for 0 psi to 30 psi gauge. This sensor comes with a barbed tube made out of polyamide, and adhesive made out of epoxy, silicone gel. Both of these materials are resistance to high concentration to pure ethyl alcohol, and isopropyl alcohol. The first design was to push the barbed tube, through a FET lined PVC pipe, to form an inline pressure sensor. However, this design leaked under pressure at a slow rate.
| Pressure sensor leak under pressure |
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In the next design, a 90-degree elbow tube connector from McMaster-Carr was modified as the sensor mount. This 90-degree connector is made out of Polycarbonate, excellent for pure alcohols. A 3.5mm acetal spacer was added between the connector and the sensor to improve flow. Acetal, also known as Derlin, is excellent for a wide range of chemicals, including pure alcohol. The parts were later glued with epoxy for strength and water seal.
A 0.1 micro Farad surface mount capacitor was solder directly onto the sensor between GND and +3V3 to ensure stability I2C communication. Here is a picture of the sensor mounted on the eDNA. The sensor use 3.3V from the feather M0, and communication via I2C protocol. Note: There are no pulled up resistors on the sensor. Add at most 10k ohm resistor between SCL, SDA and 3V3 to pull up these two lines if there no other pull up in the system.
The code utilizes the Arduino-SSC library which was designed for Honeywell TruStability™ SSC series. However, with some parameter modification, this library and its example code can work for Honeywell ABP pressure sensor series also. The code below has been modified to output correct data for only Honeywell ABPDANT030PG0D3.
setMinPressure, and setMaxPressure is based on the Min/Max pressure on the datasheet for the ABPDANT030PG0D3. The max working pressure for ABPDANT030PG0D3 is 30 psi. If want to see output:
- Unit in psi: ssc.setMaxPressure(30.0);
- Unit in kPa: ssc.setMaxPressure(206.8);
- Unit in mbar: ssc.setMaxPressure(2068.4);
What it would look like in the code:
| Part | Amount | Link | Price |
|---|---|---|---|
| Honeywell ABPDANT030PG0D3 | 1 | Mouser | $15.60 |
| 90-degree barbed connector | 1 | McMasterCarr | $1.91 |
| 0.1 uF 0850 capacitor | 1 | Mouser | $0.10 |
| Or | Digikey | $0.10 | |
| Epoxy | 1 |