Electric Field sensing (aka Capacitive sensing)

Will this be applicable to liquids which foam? Maybe via a window in the tank. If it is you have a winner on your hands.

I worked for a medical equipment manufacturer a few years ago. We were using a moving metal diaphragm in a disposable fluid management device (cartridge). The capacitive sensor was mounted in the equipment which held the disposable cartridge. The cartridge/equipment system performed many tasks. One was to regulate fluid pressure and/or vaccuum/suction (negative pressure) level.

When the cartidge was clamped securely and accurately positioned in the machine, the capacitive sensor could be calibrated. First, the fluid was exposed to current room air pressure. Secondly, a known fluid pressure was entered and measured by hanging an IV bag at a known height above the cartridge. A PC then completed the calibration by comparing the two measurements. The movement of the diaphragm towards the sensor (positive pressure) or away from the sensor (negative pressure) was then translated by the PC and displayed on screen as fluid pressure (mm of Hg, or whatever units desired).

We had a lot of problems with consistency and calibration, due, in part, to the limited range of the sensor we were using. A sensor with a higher capacity or range would have made this system work much better.

Could have important applications in homeland security. But I'm kinda skeptical about the existence of dielectric constants less than one!

Can you change the sensitivity range of the cap.sensor? Say you wanted a range of 10 mm and also through a plastic material, is that possible?

Also, if this were to be used in an application where the sensor would activate upon recognition of a hand(skin), can you eliminate false detection (i.e. water, anything but a hand or gloved hand)???

What is that supply current being drawn for constant operation to sense objects?

Can it detect contamination [glass or plastic] in a food product? Garthh