Capacitance Diaphragm Gauge Reference Cavity Gas Detection
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Solution Overview
Problem
Capacitance diaphragm gauges (CDGs) face accuracy issues due to changes in the reference vacuum cavity pressure, which are difficult to detect, leading to negative zero shifts and diagnostic challenges, as the sealed nature of the cavity prevents detection of gas molecule degradation and differentiation from other phenomena causing similar shifts.
Innovation Solution
An independent pressure transducer with a ring anode, cathode, and magnet is inserted into the reference vacuum cavity, applying a high voltage to ionize gas molecules and measure current flow, activating an alarm when the current exceeds a predetermined magnitude, and optionally removing ionized gas molecules by sputtering them onto the cathode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the reference vacuum cavity is sealed to maintain constant reference pressure, then the zero point stability is improved, but the ability to detect gas molecule degradation is lost
Solution Approach 1:
A pressure transducer is introduced as an intermediary device within the sealed reference vacuum cavity to indirectly detect gas molecule degradation. The transducer measures pressure changes caused by accumulating gas molecules without requiring opening the sealed cavity, thus maintaining zero point stability while enabling detection of degradation.
2Reliability
If getter material is used to absorb gas molecules in the reference vacuum cavity, then the reference pressure stability is improved, but the ability to distinguish actual leaks from other phenomena is lost
Solution Approach 1:
The pressure transducer provides continuous feedback on the pressure within the reference vacuum cavity. By monitoring pressure changes over time and comparing them against expected patterns, the system can distinguish between actual gas leaks (which would show specific pressure increase patterns) and other phenomena such as temperature variations or getter material saturation, thus preserving diagnostic information while maintaining reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This system effectively detects and addresses unacceptable gas molecule quantities in the reference vacuum cavity, preventing accuracy degradation and enabling timely replacement of the CDG, thus maintaining measurement integrity.
Implementation Method 1
A high voltage source applies a voltage between the ring anode and the cathode to ionize gas molecules. A current sensor senses a magnitude of any current flowing between the ring anode and the cathode via ionized gas molecules.
Implementation Method 2
A magnet is positioned with respect to the ring anode such that the magnetic flux of the magnet is generally aligned with the central axis of the ring anode.
Implementation Method 3
The independent pressure transducer causes ionized gas molecules to be sputtered onto the cathode to thereby remove ionized gas molecules from the reference vacuum cavity.
Data Source
AI summary
A system and method detect the presence of an unacceptable quantity of gas molecules in the reference vacuum cavity of a capacitance diaphragm gauge (CDG). An independent pressure transducer has an active portion exposed to the reference vacuum cavity. The transducer includes a ring anode, a cylindrical inner wall surface that forms at least one cathode, and a magnet positioned with respect to the ring anode such that the magnetic flux of the magnet is generally aligned with the central axis of the ring anode. A high voltage source applies a voltage between the ring anode and the cathode. A current sensor senses a magnitude of any current flowing between the ring anode and the cathode via ionized gas molecules. A monitoring unit monitors the magnitude of the current sensed by the current sensor and activates an alarm when the magnitude of the current exceeds an acceptable magnitude.