Apparatus and method for automatic detection of diaphragm coating or surface contamination for capacitance diaphragm gauges

A contamination detection system for a capacitance diaphragm gauge (CDG), the CDG including a diaphragm and at least one fixed electrode wherein the capacitance between the diaphragm and the at least one fixed electrode is responsive to a pressure applied to the CDG that deflects the diaphragm with respect to the at least one fixed electrode, the system comprising:

• a source of a DC voltage;
• a switch to selectively apply the DC voltage between the diaphragm and the at least one fixed electrode in the CDG, the diaphragm responsive to the applied DC voltage to deflect the diaphragm with respect to the at least one fixed electrode;
• and
• a contamination test controller having an output that selective enables the switch and having an input that receives pressure values responsive to the deflection of the diaphragm with respect to the at least one fixed electrode, the contamination test controller comparing a first pressure value before enabling the switch with a second pressure value while enabling the switch to determine a difference between the first and second pressure values, the contamination test controller determining the presence of unacceptable contamination when the difference in the first and second pressure values is less than a predetermined pressure difference.