Flow Sensor Output Compensation for Sub-Minimum Range Valve Control
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Solution Overview
Problem
HVAC systems face challenges in accurately measuring and controlling fluid 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 calculating a corrected flow rate by determining a minimum valve position threshold and a minimum flow rate threshold, using interpolation methods such as polynomial or exponential functions, to compensate for measurements below the sensor's readable range, and controlling valve operations accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If flow rate sensor is used to measure flow rate, then flow rate measurement is obtained, but measurement precision deteriorates when flow rate is 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 measurable parameters (valve position, pressure differential) to infer flow rates in the sub-minimum range, acting as a bridge that translates unreliable sensor readings into reliable control information through mathematical relationships.
Solution Approach 2:
The patent replaces the mechanical/sensor-based measurement system with a computational model-based estimation system for low-flow conditions. Instead of relying on the physical sensor to directly measure sub-minimum flow rates, the system substitutes sensor data with calculations derived from valve position and pressure differential measurements, effectively replacing the sensor's direct measurement function with an indirect computational approach.
2Adaptability or versatility
If flow rate sensor working range is limited, then device complexity is reduced, but adaptability deteriorates for flows outside working range
Solution Approach 1:
The patent makes the control system universal by enabling it to handle both normal-range and sub-minimum flow rates through a single integrated approach. The computational model serves multiple functions: it validates sensor readings in the normal range and provides estimated readings in the sub-minimum range, allowing the same system architecture to adapt to varying flow conditions without requiring additional hardware or complex switching mechanisms.
Solution Approach 2:
The patent changes the operational parameters of the control system by introducing calculated parameters (estimated flow rate, minimum readable flow threshold) that complement the sensor's direct measurements. By monitoring parameter transitions (when measured flow approaches minimum readable flow) and switching between direct sensor usage and model-based estimation, the system adapts to different flow regimes while maintaining manageable complexity through parameter-driven control logic.
3Ease of operation
If valve control is used to achieve desired flow, then flow control capability is improved, but difficulty of detecting and measuring worsens when flow is below sensor range
Solution Approach 1:
The patent implements a feedback mechanism where the computational model continuously monitors the relationship between valve position, pressure differential, and measured flow rate. When the measured flow approaches the minimum readable threshold, the model provides feedback to switch to estimation mode, ensuring continuous accurate flow information is available to the control system regardless of whether the sensor can directly measure the current flow condition.
Solution Approach 2:
The patent performs preliminary action by pre-establishing the computational model and minimum readable flow threshold before actual control operations begin. The system proactively detects when flow is approaching the sensor's minimum range and switches to model-based estimation in advance, preventing measurement gaps rather than reacting to them, thereby maintaining continuous flow awareness throughout the control process.
Data Source
AI summary
A system for monitoring and controlling flow rate of a fluid through a valve, the system including a flow rate sensor configured to measure the flow rate of the fluid through the valve, and a controller in communication with the flow rate sensor. 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. In response to determining equality, the controller is configured to determine a minimum valve position threshold (xmin), and determine a minimum flow rate threshold (ymin) corresponding to xmin. The controller is further configured to calculate a corrected flow rate (ŷf) using xmin, ymin, and an indication of valve position (v). Additionally, the controller is configured to control a valve operation using the corrected flow rate (ŷf).