Capacitance manometers are electro-mechanical gauges that can measure both pressure and vacuum. The capacitance gauge translates a pressure-modulated movement in a thin diaphragm into an electrical signal proportional to the pressure. The pressure sensor is the thin diaphragm that is exposed to the pressure or vacuum being measured via the inlet tube. An electrode is mounted in the reference cavity behind the diaphragm. Pressure differences between the process and the reference cavity deflect the diaphragm slightly, changing the distance between it and the electrode. Variations in this distance produce variations in the capacitance between the diaphragm and the electrode creating an electrical signal that is proportional to the pressure change. Since differences in the capacitance signal are produced by physical changes within the manometer and not by changes in the gas properties, pressure measurements by the capacitance manometer are independent of the composition of the gas being measured.

These capacitance manometers are temperature controlled to 45°C or 100°C for improved accuracy. Unheated versions are exposed to ambient temperature variations which can degrade the sensor accuracy. These devices have the sensor enclosed in a volume that is maintained at a constant temperature above ambient. This solution improves the manometer’s accuracy and repeatability and lowers instrument drift by reducing or eliminating process contamination within the manometer. Heated manometers are recommended for applications that require maximum accuracy and repeatability, operate above ambient temperature and for those processes that employ hot gases.