Ion Current Gas Detector Shielding for Faster Stable Sensing
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Solution Overview
Problem
In fast vacuum applications, previous current amplifiers in the lower current range are the slowest link in the signal chain, and conventional measuring resistors used to measure ion current suffer from high parasitic stray capacitances and reduced stability when amplifying ion current, especially with electron multipliers.
Innovation Solution
The implementation of an electrical shield resistor surrounding the measuring resistor, with both resistors having opposing ends connected to the same potential, and the shield resistor having a lower resistance value than the measuring resistor, effectively eliminating parasitic stray capacitances by maintaining a comparable voltage drop across both resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-ohm measuring resistors (around 500 gigaohms) are used to measure ion current, then noise component in the measuring signal is kept low, but parasitic stray capacitances are produced which slow down the response time
Solution Approach 1:
The patent applies equipotentiality by surrounding the measuring resistor with a shield resistor and applying the same potentials to mutually opposed regions of both resistors. This creates a comparable voltage drop across both resistors, eliminating current flow through parasitic capacitances and thereby reducing their harmful effect on response time while maintaining the high resistance needed for low noise measurement
2Power
If conventional current amplifiers are used in the lower current range, then ion current can be amplified, but they are the slowest link in the signal chain
Solution Approach 1:
The patent changes the electrical parameters of the measuring system by introducing a shield resistor with lower resistance value than the measuring resistor. This parameter change creates a different voltage distribution that reduces the time constant of the system, thereby speeding up the response of the current amplifier without sacrificing its amplification capability
3Speed
If electron multipliers are used to amplify ion current, then response time is reduced, but stability decreases
Solution Approach 1:
The shield resistor acts as an intermediary element between the measuring resistor and the surrounding environment. It mediates the electrical field distribution around the measuring resistor, creating a stable potential environment that reduces parasitic capacitance effects. This allows the system to achieve fast response times without the instability associated with electron multipliers
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 configuration enhances the response time and stability of the gas detector by reducing parasitic capacitances and noise in the signal, allowing for more efficient measurement of ion currents without the drawbacks of conventional high-ohm resistors.
Implementation Method 1
an ionizing device (12) for producing ions depending on a gas type (20) to be detected and for producing an ion current depending on the ions
Implementation Method 2
A measurable electrical measuring potential is produced from the amplified current by means of an electrical measuring resistor (16)
Implementation Method 3
the measuring resistor (16) is surrounded at least in part by an electrical shield resistor (RT) and the same potentials up to a deviation of at most 25% are applied in the longitudinal direction of the measuring resistor (16) to mutually opposed regions of the measuring resistor (16) and the shield resistor (RT)
Data Source
AI summary
The disclosure provides a gas detector with an ionizing device for producing ions depending on a gas to be detected. The gas detector includes a catcher for receiving the electrical current produced by the ions, and a measuring device with an electrical measuring resistor. The electrical measuring resistor produces an electrical measuring potential from the current and is surrounded, at least in part, by an electrical shield resistor, denoted by RT. The same potentials, up to a deviation of at most 25%, are applied in the longitudinal direction of the electrical measuring resistor to mutually opposed regions of the electrical measuring resistor and the electrical shield resistor.