Cold Cathode Ionization Gauge Multiple Cathodes Wide Pressure Range
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Solution Overview
Problem
Cold cathode ionization gauges (CCIGs) are limited to measuring pressures below 10^-2 Torr and require additional gauges for higher pressure ranges, as they cannot accurately measure pressures up to atmospheric levels due to instability and inaccuracies in discharge current measurements at higher pressures.
Innovation Solution
A CCIG design with a second cathode and an electronic controller that applies different electric potential gradients between the common anode and independent cathodes, allowing for ionization and pressure measurement at both low and high pressures through Townsend and Paschen's Law discharges, using distinct current and impedance measurements to determine pressure across a wide range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single cathode design is used, then the gauge can measure low pressures (below 10^-2 Torr) accurately, but it cannot measure higher pressures up to atmospheric levels due to instability and inaccuracies in discharge current measurements
Solution Approach 1:
The single cathode is divided into multiple cathode segments (first cathode segment, second cathode segment, third cathode segment) with different spacing from the anode. Each segment operates optimally in different pressure ranges, allowing the gauge to measure from 10^-11 Torr to atmospheric pressure (760 Torr) accurately across the entire range.
Solution Approach 2:
Different cathode segments are positioned at different distances from the anode to create local variations in electric field strength and discharge characteristics. The first cathode segment (closer to anode) is optimized for high pressure measurement, while the second and third segments (farther from anode) are optimized for low pressure measurement, with each segment having tailored spacing to achieve optimal performance in its specific pressure range.
2Stability of the object's composition
If the cathode spacing from anode is fixed, then the discharge current measurement is stable at that spacing, but the gauge cannot adapt to different pressure ranges requiring different optimal spacings
Solution Approach 1:
The cathode is segmented into multiple sections with fixed but different spacing from the anode. Each segment maintains stable discharge current characteristics at its specific spacing, while collectively covering a wide pressure range. The segments are electrically connected in parallel to sum their currents for total pressure measurement.
Solution Approach 2:
The system dynamically selects which cathode segments are active based on pressure conditions. At different pressures, different segments contribute differently to the total current measurement, allowing the gauge to adapt to varying pressure ranges while maintaining measurement stability through the fixed spacing design of each segment.
3Adaptability or versatility
If multiple cathodes with different spacings are used, then the gauge can measure a wide pressure range, but the device complexity increases
Solution Approach 1:
Multiple cathode segments with different spacings are merged into a single cathode structure that is electrically connected in parallel. This combining approach allows the gauge to achieve wide pressure range coverage (10^-11 to 760 Torr) while maintaining a relatively simple overall structure, as the segments share common mounting and electrical connection infrastructure rather than requiring completely separate gauge components.
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
Enables accurate pressure measurement from 10^-11 Torr to atmospheric pressure (760 Torr) by stabilizing plasma discharge and reducing measurement inaccuracies, eliminating the need for additional gauges and improving sensitivity and linearity across the pressure range.
Implementation Method 1
A magnetic field is applied along the axis of the electrodes perpendicular to the electric field in order to lengthen free electron paths to sustain a pure electron plasma
Implementation Method 2
A high DC voltage potential difference is applied between the anode electrode and the cathode electrode to create an electronic field between the electrodes
Implementation Method 3
electrons collide with molecules and atoms to create ions
Implementation Method 4
As a result of the crossed electric and magnetic fields, a pure electron plasma builds as a sheath around the anode
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A cold cathode ionization gauge includes multiple cathodes providing different spacings between the cathodes and an anode. The multiple cathodes allow for pressure measurements over wider ranges of pressure. A first cathode with a larger spacing may provide current based on Townsend discharge; whereas, a second cathode having a smaller spacing may provide current based on both Townsend discharge at higher pressures and on Paschen's Law discharge at still higher pressures. A feature on the second cathode may support Paschen's Law discharge. Large resistances between the cathodes and a return to power supply enable control of output profiles to extend the pressure ranges with accurate responses and avoid output minima. Pressure measurements may be made based on currents from respective cathodes dependent on the outputs of the cathodes through the wide pressure range of measurement. The multiple cathodes may also provide measurements that avoid the discontinuities found in current outputs of the respective cathodes.