High-Temperature Gas Flow Control with External Thermistor Correction
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Solution Overview
Problem
The existing pressure type flow rate control devices for high-temperature gases suffer from reduced accuracy due to temperature measurement errors caused by the thermistor temperature detector's individual variability and temperature gradients within the valve body, leading to significant flow rate control errors, especially at higher temperatures.
Innovation Solution
The solution involves positioning the thermistor temperature detector above the outlet side fluid passage between the valve portion and the restriction mechanism, with a jacket heater used to heat the valve body, and employing a detected value correcting element to correct temperature measurement errors based on temperature characteristics, ensuring accurate flow rate control by minimizing the difference between detected and actual gas temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the temperature detector is positioned closer to the gas passage to improve temperature detection accuracy, then the detected temperature better reflects actual gas temperature, but the device size increases and maintenance accessibility deteriorates
Solution Approach 1:
The patent positions the temperature detector on the outer surface of the valve body rather than inside the gas passage, changing the detection dimension from internal to external. This external positioning maintains adequate maintenance accessibility while the correction table compensates for the temperature gradient to preserve measurement accuracy.
2Temperature
If the thermistor temperature detector is used for high-temperature gas measurement, then the device can operate at elevated temperatures, but individual variability of the thermistor causes significant measurement errors, reducing reliability
Solution Approach 1:
The patent establishes a feedback mechanism where the detected temperature is continuously corrected using the correction table, and this corrected temperature is then used for flow rate control calculations. This feedback loop compensates for individual thermistor variability and maintains reliable flow rate control across the operating temperature range.
3Temperature
If the valve body is heated using a jacket heater to maintain gas temperature, then the gas temperature can be controlled, but the temperature gradient within the valve body increases, worsening temperature measurement accuracy
Solution Approach 1:
The patent performs preliminary correction of the temperature measurement by using the correction table to account for the temperature gradient caused by jacket heating. This preliminary action compensates for the expected measurement error before the temperature data is used for flow rate control, maintaining accuracy despite the presence of temperature gradients.
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 achieves high-accuracy flow rate control for gases at 50 to 500°C with an error of ±1.0% F.S., improving maintenance accessibility and reducing the overall size of the gas supply device by correcting temperature measurement errors and maintaining precise temperature correction.
Implementation Method 1
with a jacket heater used to heat the valve body
Implementation Method 2
the thermistor temperature detector's individual variability and temperature gradients within the valve body
Data Source
AI summary
A pressure type flow rate control device provides flow rate control for gas at 100-500° C. with an error not more than 1.0% F.S. The pressure type flow rate control device includes a valve body with a fluid passage, a valve portion interposed in the passage, a valve drive unit driving the valve portion to open/close the passage, a restriction mechanism on the downstream side of the valve portion in the passage, a temperature detector detecting gas temperature between the valve portion and restriction mechanism, a pressure detector detecting gas pressure between the valve portion and restriction mechanism, and an arithmetic control device controlling flow rate of gas in the restriction mechanism based on values detected by the temperature detector and the pressure detector, wherein the temperature detector is inserted in an attachment hole of the valve body at a position just above an outlet side fluid passage.