Technical reports: Liquid presence sensing

Water-based Liquid Detection

At LAIIER we have carried out a series of tests for our Severn sensors to show their performance for a range of liquids and setups. Here, we present a technical report for the Severn sensor when in contact with water-based liquids.

Test A: Tap water sensitivity

Measuring the response of the Severn sensor when in contact with different amounts of tap water. We want to show how precisely the sensor can detect water droplets and how larger quantities affect the sensor reading.

Procedure

Setup for measuring water sensitivity on the Severn sensor

First, the sensitivity of the Severn sensor was tested with tap water. A micropipette was used to drop increments of 0.02, 0.03, 0.04, 0.05, 0.1 and 0.5 ml of tap water onto the sensor at a fixed height.

The Severn sensor was connected to the Severn board in order for serial data to be collected. For every test, the tap water was dispensed at five seconds.

Results and findings

  • As the graph shows, 0.02 ml of tap water can be detected with a clear drop in sensor reading. 
  • Greater amounts of tap water (0.03 ml - 0.5 ml) have an increasingly larger drop in sensor reading.
Graph showing the water sensitivity of the Severn sensor

Test B: Varying water type

Measuring the response of the Severn sensor when in contact with water-based liquids, namely:

  • Distilled water
  • Brackish water (1.5% salt)
  • Saline water (4% salt)
  • Brine water (15.5% salt)

Testing these variations will show how different concentrations of salt affect the sensor reading.

Procedure

Setup for varying water type on the Severn sensor

Salt solutions were made by dissolving sea salt into distilled water at the noted concentrations. A micropipette was used to dispense 0.1 ml of each liquid onto the Severn sensor at a fixed height.

The Severn sensor was connected to the Severn board in order for serial data to be collected. All drops were dispensed at five seconds.

Results and findings

  • The graph shows that all types of salt solutions produced a significant sensor reading drop. 
  • Distilled water can be detected with a slightly smaller drop in reading
Graph showing water-based detection on the Severn sensor

Conclusion

In summary, the Severn sensor can detect as little as 0.02 ml of tap water. As more tap water is dispensed from 0.02 ml to 0.5 ml, the greater the change in sensor reading.

All salt solutions can be detected with a similar signal change while distilled water can be distinguished with a smaller signal change.