Mass Flow Controller Temperature Measurement Using Thermal Sensor
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Solution Overview
Problem
Mass flow controllers (MFCs) face temperature-related inaccuracies, such as zero shift, which can be compensated by knowing the gas temperature, but adding a separate temperature sensor increases complexity and cost.
Innovation Solution
Derive gas temperature measurements from the existing thermal mass flow sensor by supplying a constant electrical current, measuring input voltage variations, and calculating adjusted voltages to determine gas temperature, thereby avoiding the need for a separate temperature sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate temperature sensor is added to the MFC to measure gas temperature for compensation, then temperature measurement capability is improved, but device complexity and cost increase
Solution Approach 1:
The thermal mass flow sensor is made to serve dual purposes: measuring both mass flow rate and gas temperature. By supplying constant current to the sensor and measuring input voltage variations, the system extracts temperature information from the existing sensor's electrical characteristics without requiring additional temperature sensing elements.
Solution Approach 2:
The existing thermal mass flow sensor serves itself by providing temperature measurement capability through its own electrical properties. The sensor's input voltage, when supplied with constant current, varies with temperature differential, allowing the sensor to self-diagnose and provide temperature data without external assistance.
2Measurement precision
If a separate temperature sensor is added to the MFC to measure gas temperature for compensation, then temperature measurement capability is improved, but cost increases
Solution Approach 1:
The thermal mass flow sensor is made to serve dual purposes: measuring both mass flow rate and gas temperature. By supplying constant current to the sensor and measuring input voltage variations, the system extracts temperature information from the existing sensor's electrical characteristics without requiring additional temperature sensing elements.
Solution Approach 2:
The existing thermal mass flow sensor serves itself by providing temperature measurement capability through its own electrical properties. The sensor's input voltage, when supplied with constant current, varies with temperature differential, allowing the sensor to self-diagnose and provide temperature data without external assistance.
3Device complexity
If the MFC operates without temperature compensation, then device complexity remains low, but temperature-related inaccuracies such as zero shift increase
Solution Approach 1:
The system uses feedback from the thermal mass flow sensor's electrical characteristics to compensate for temperature-related inaccuracies. By continuously monitoring input voltage variations and calculating temperature, the system adjusts measurements to correct for zero shift and other temperature-dependent errors, improving reliability without adding complex hardware.
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 method improves temperature insensitivity and reduces complexity and cost by using existing sensors to measure and compensate for temperature-related inaccuracies in MFCs.
Implementation Method 1
supplying a substantially constant electrical current to a thermal mass flow sensor... measuring an input voltage of the thermal mass flow sensor to obtain a present input voltage, the input voltage varying with a temperature differential between a pair of sensing elements
Data Source
AI summary
A method and apparatus for measuring the temperature of a gas in a mass flow controller is described. One embodiment derives gas-temperature information from a mass flow sensor of the mass flow controller without relying on a separate temperature sensor. This embodiment supplies a substantially constant electrical current to a thermal mass flow sensor of the mass flow controller, the thermal mass flow sensor being designed to measure a mass flow rate of the gas; measures an input voltage of the thermal mass flow sensor to obtain a present input voltage, the input voltage varying with a temperature differential between a pair of sensing elements of the thermal mass flow sensor; calculates an adjusted input voltage by accounting for a component of the present input voltage that is dependent on the mass flow rate of the gas; and calculates the temperature of the gas based on the adjusted input voltage. In some embodiments, the calculated gas temperature is used to compensate for the variation, with temperature, of an output voltage of the thermal mass flow sensor under a zero-flow condition.