The manometer senses atmospheric pressure on one end, and a chamber pressure at the other. Steel wire is wrapped around the aluminum bottle, and when electricity is applied to the wire, heat is generated and conducted through the aluminum bottle to the air contained inside. As the temperature rises, so does the chamber pressure. When the liquid level drops below the sensor, electricity is applied to the wire coil until the chamber pressure equilibrates with the atmospheric pressure, and the liquid level rises above the sensor. A solid state thermocouple is attached to the aluminum container, whose voltage is a function of temperature.
Additional circuitry allows for zeroing the sensor, and amplifying and filtering the voltage signal.
The device is calibrated using the specific gravity of the manometer fluid, and measuring the temperature difference for two different fluid heights at a constant atmospheric pressure. The thermocouple voltage can be read by RTX and filtered, converted, and scaled into an appropriate pressure reading. A VB interface facilitates the displaying and saving of data. For manometers, a change in pressure causes a change in fluid height. Inclining the fluid tube amplifies the changes in pressure by causing the fluid to move a large distance to achieve a small height difference.