Interrupted DC Heating for Thermocouple Vacuum Gauge Accuracy
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Solution Overview
Problem
Thermocouple vacuum gauges used in cryopump controllers lack accuracy and complexity due to the need for high-frequency alternating current to heat the sensor wire, making them expensive and difficult to calibrate for pressure measurement in the range of 0.001 to 1 Torr.
Innovation Solution
A thermocouple-type vacuum sensor uses direct current voltage to heat the sensor wire, allowing for sampling of unbiased sensor voltage after stopping the current flow, which simplifies the system and reduces complexity by eliminating the need for high-frequency AC excitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-frequency alternating current is used to heat the sensor wire in a thermocouple vacuum gauge, then accurate pressure measurement is achieved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the high-frequency AC excitation requirement from the system by using DC heating instead, eliminating the need for complex AC signal generation and synchronization circuitry while maintaining measurement capability through periodic sampling
Solution Approach 2:
The patent changes the heating current parameter from high-frequency alternating current to direct current, fundamentally altering the excitation method to simplify the system architecture while achieving equivalent measurement results through DC heating with periodic interruption
2Measurement precision
If high-frequency alternating current is used to heat the sensor wire, then pressure measurement functionality is maintained, but manufacturing cost increases
Solution Approach 1:
The patent employs inexpensive DC voltage sources and simple switching components instead of expensive AC signal generators, using readily available electronic components to reduce manufacturing costs while maintaining measurement functionality
Solution Approach 2:
The patent removes the expensive AC excitation subsystem including function generators and frequency synthesizers, replacing them with simple DC voltage sources and switches, thereby dramatically reducing bill of materials cost
3Stability of the object's composition
If continuous current flow is used to heat the sensor wire, then stable temperature is maintained, but measurement accuracy decreases due to DC offset
Solution Approach 1:
The patent implements periodic interruption of the DC heating current, switching between heating mode and measurement mode in cycles, which eliminates the DC offset in the thermocouple output while maintaining temperature stability through rapid thermal response and controlled duty cycle
Solution Approach 2:
The patent applies preliminary heating to bring the sensor wire to the desired temperature before measurement, then interrupts the heating current specifically during the measurement phase to eliminate offset, separating the heating and measurement functions in time
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 approach provides accurate pressure measurements within the 0.001-10 Torr range with minimal error, reducing costs and complexity by using direct current heating and sampling, suitable for cryopump controllers.
Implementation Method 1
passing a current through a wire, e.g. a nickel wire, so that it gets hot
Implementation Method 2
Thermocouples are based on the Seebeck effect named after Thomas Seebeck, who discovered it in 1821 and which describes the voltage created whenever two dissimilar metals touch
Implementation Method 3
Within this pressure range the thermal conductivity of air increases with increasing pressure and thus can be used to measure the pressure
Data Source
AI summary
A direct current voltage to heat the sensor wire for powering and extracting a signal voltage from a thermocouple-type vacuum sensor. The direct current used produces a DC offset in the sensor output where the heating current flow is stopped for a short interval and the unbiased sensor voltage is then sampled and stored.