A common reason for drift on a capacitance manometer is due to condensation on the diaphragm. A capacitance manometer has a thin diaphragm inside. As molecules collide with the diaphragm, it deflects, which is then correlated to a pressure. If there is condensation of the diaphragm, it is already deflected a certain amount, which will cause the unit to measure incorrectly. This can be alleviated by zeroing the unit. Instructions for this can be found in the manual.
Category: Instrumentation Gauging
Sub-Category: Capacitance Manometers