Capacitive Volume Sensing

Project Goal: Create a contactless liquid level sensor that can measure levels of tissue staining reagent with high accuracy, resolution and precision

The HE 600 machine automates tissue staining to diagnose diseases such as cancer. It dispenses reagents on top of tissue samples, which are fixed to microscope slides. The reagents are housed in 1-liter reservoirs, which use mechanical signal floats to determine liquid level. The floats are in direct contact with the reagents and so break down easily, putting excess strain on system pumps that need constant replacements. In addition, the floats also often get stuck or corroded, and thus do not accurately measure reagent levels.

This design uses contactless capacitive sensing to constantly measure the liquid level inside the reservoir. The system has a flexible printed circuit board (the sensor) and a small metal box containing the capacitive sensor chip and microcontroller. The entire system is adhered to the outside of the reservoir so that none of the components are in contact with the reagents.

The system provides real-time liquid volume levels via USB connection to a computer station with a graphical user interface. This design is meant to last the lifetime of the HE 600,creating a cost-effective and long-lasting volume measuring system.