Mass Flow Controller Feedback Filtering for Faster Thermal Sensor Response
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Mass flow controllers (MFCs) face challenges in achieving high response speed due to the slow response characteristics of thermal flow rate sensors, which are limited by the heat transport rate of fluids through the sensor tube and heat-generating resistor, resulting in a time constant of about 10 seconds, and existing pressure-based MFCs do not achieve fast response speed feedback control.
Innovation Solution
A flow rate control device with a feedback loop configuration including a flow sensor, a controller, a control valve, a drive circuit, a sensor response adjustment circuit, and filters to adjust the frequency response of the sensor output, where a deviation between the set flow rate and filtered output drives the control valve, enhancing response accuracy by attenuating specific frequency bands and amplifying others outside the feedback loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermal flow rate sensor is used to measure fluid flow, then the sensor provides flow rate measurement capability, but the response speed is slow with a time constant of about 10 seconds due to heat transport limitations
Solution Approach 1:
The patent implements feedback control by feeding back the sensor output signal through the drive circuit to the control valve. This closed-loop feedback mechanism continuously adjusts the control valve based on the difference between the target flow rate and actual measured flow rate, enabling high-precision flow rate control despite the slow sensor response characteristics.
Solution Approach 2:
The patent changes the response characteristics parameter of the sensor output signal by processing it through the drive circuit and sensor response adjustment circuit. By adjusting gain parameters and frequency response characteristics, the system compensates for the inherently slow thermal response of the flow rate sensor, achieving faster effective response without changing the physical sensor itself.
2Adaptability or versatility
If pressure-based MFC is used instead of thermal MFC, then different measurement approach is provided, but fast response speed feedback control is still not achieved
Solution Approach 1:
The patent replaces traditional mechanical pressure-based measurement systems with an electrical signal processing system. By substituting mechanical pressure sensing with electrical sensor output signal processing through the drive circuit and sensor response adjustment circuit, the system achieves faster response speeds while maintaining measurement accuracy.
3Device complexity
If the sensor output signal is directly used for control, then the control system is simple, but the response accuracy is insufficient due to slow sensor response characteristics
Solution Approach 1:
The patent merges the sensor output signal processing functions with the existing drive circuit that controls the control valve. By integrating the sensor response adjustment circuit with the drive circuit, the system achieves improved response accuracy without adding significant complexity, as both circuits work together in a unified feedback control loop.
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
The solution enables a high response accuracy and faster response speed, approximately twice that of existing technologies, by accelerating feedback control and improving the reflection of actual flow rates in display values, even with thermal flow rate sensors.
Implementation Method 1
response characteristics of the thermal MFC are lower than theoretical values predicted from the response characteristics of the thermal flow rate sensor in actual measurement, and only a slow response with a time constant of about 10 seconds can be obtained. This is because a heat transport rate by the fluid such as gas flowing through the flow path is small with respect to a heat capacity of a sensor tube and a heat-generating resistor.
Data Source
AI summary
A flow rate control device having a high response accuracy is provided.A flow rate control device includes a flow sensor measuring a flow rate of a fluid, and a controller adjusting the flow rate where the flow rate of the fluid to be a flow rate set value. The controller includes a control valve changing the flow rate, a drive circuit driving the control valve, a sensor response adjustment circuit adjusting a frequency response of a measured value of the flow sensor, and a first filter attenuating a predetermined frequency band of an output of the sensor response adjustment circuit. The drive circuit, the flow sensor, the sensor response adjustment circuit, and the first filter, configure a feedback loop. A deviation between the flow rate set value and an output of the first filter becomes an input to the drive circuit.