Flow Sensor PWM Compensation for Low-Flow HVAC Control
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Solution Overview
Problem
HVAC systems face challenges in accurately measuring and controlling flow rates outside the working range of flow rate sensors, leading to unreliable measurements and difficulty in reaching desired flow setpoints.
Innovation Solution
A system that includes a flow rate sensor and a controller capable of generating a pulse-width modulated signal to calculate a corrected flow rate, allowing the system to operate the valve effectively even when measurements are below the minimum readable flow rate, by determining a minimum valve position threshold and a minimum flow rate threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a flow rate sensor is used to measure flow rates, then flow rate measurement is enabled within the working range, but measurements become unreliable outside the working range (below minimum readable flow)
Solution Approach 1:
The patent introduces an intermediary computational model that mediates between the sensor's limited measurement capability and the control system's need for accurate low-flow data. The model uses PWM signal characteristics (duty cycle, frequency) in conjunction with valve position feedback to estimate actual flow rates when they fall below the sensor's minimum readable threshold, thereby bridging the measurement gap without requiring hardware modification.
Solution Approach 2:
The patent replaces the mechanical/physical measurement limitation of the flow sensor with a computational approach. Instead of relying solely on the sensor's physical detection capabilities, the system substitutes a mathematical model that processes electrical signals (PWM) and feedback data to compute flow rates, effectively replacing the sensor's insufficient measurement function with a software-based solution.
2Reliability
If the flow rate sensor's working range is used as the control range, then reliable measurements are obtained within this range, but the system cannot reach desired flow setpoints below the minimum readable flow
Solution Approach 1:
The patent implements dynamic adaptation of the control system by continuously monitoring the relationship between PWM signals, valve position, and measured flow rates. The computational model dynamically adjusts its estimates based on real-time system state, allowing the control range to extend below the sensor's minimum readable flow while maintaining reliability through continuous validation against actual sensor readings when available.
Solution Approach 2:
The patent employs feedback mechanisms where the controller receives both the measured flow rate from the sensor and the actual valve position, then uses this feedback to refine the computational model's estimates. This closed-loop feedback ensures that even when operating below the sensor's minimum readable flow, the system can accurately determine actual flow rates and adjust valve positioning to achieve desired setpoints.
3Measurement precision
If PWM signal processing is implemented to calculate corrected flow rates, then control accuracy is improved outside the sensor's working range, but system complexity increases
Solution Approach 1:
The patent achieves universality by designing a computational model that serves multiple functions: it accurately calculates flow rates both within and outside the sensor's working range using the same algorithmic framework. The model processes PWM signals and valve position data to provide reliable flow rate estimates across the entire operational range, eliminating the need for separate measurement systems or complex conditional logic while maintaining high precision throughout.
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AI summary
A system for monitoring and controlling flow rate of a fluid through a valve is disclosed. The system includes a flow rate sensor to measure the flow rate of the fluid through the valve, and a controller. The controller is configured to receive the measured flow rate from the flow rate sensor, and determine if the measured flow rate is equal to a predetermined flow rate value. The controller is further configured to, in response to a determination that the measured flow rate is equal to the predetermined flow rate value, determine a minimum valve position threshold (xmin). Additionally, the controller is configured to determine a minimum flow rate threshold (ymin) corresponding to xmin, and configured to generate a PWM signal and calculate a corrected flow rate (ŷf) using the PWM signal. The controller controls a valve operation using ŷf. The PWM signal switches between zero and ymin.