Capacitive Infusion Pump Flowmeter for Closed-Loop Low-Rate Accuracy
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Solution Overview
Problem
Conventional infusion pumps lack accurate flow measurement across a broad range of fluid flow rates, especially at low rates, and require direct fluid contact, leading to contamination and high costs.
Innovation Solution
An integrated capacitive flowmeter that measures fluid volume indirectly using a conductive plate and conductor to determine capacitance, allowing for self-calibration and self-adjustment, eliminating the need for direct fluid contact and reducing inaccuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thermal transfer flowmeters are used, then flow measurement is possible, but direct fluid contact causes contamination and high costs
Solution Approach 1:
The patent introduces an intermediary capacitive sensing system that measures fluid flow without direct contact. The flowmeter uses capacitance changes detected by a sensor near the infusion line to infer fluid presence and flow characteristics, eliminating the need for direct thermal contact while maintaining measurement capability through electromagnetic field interaction with the fluid dielectric properties
Solution Approach 2:
The patent replaces the thermal transfer mechanism with a capacitive sensing mechanism. Instead of using thermal conduction between a sensor and fluid, the system uses electrical capacitance measurements that are influenced by the fluid's dielectric constant, substituting a mechanical/thermal contact-based system with an electrical field-based system that avoids contamination
2Adaptability or versatility
If conventional flowmeters are used, then measurement is possible, but the dynamic range is limited to 10:1 while infusion pumps require 10000:1
Solution Approach 1:
The patent implements a dynamic measurement system that adapts to varying flow rates by using the pump's existing cam-driven hammer mechanism to periodically compress the infusion line. The capacitive sensor dynamically tracks capacitance changes during each compression cycle, allowing the system to measure both very low flow rates (single mL/hr) and high flow rates (thousands of mL/hr) with appropriate sensitivity adjustment
Solution Approach 2:
The patent creates a universal flow measurement system that works across the entire infusion pump operating range. The capacitive sensing mechanism combined with the pump's mechanical compression cycle provides a multi-functional approach that can detect fluid presence, measure flow rate, and adapt to different infusion sets, achieving both wide dynamic range and acceptable accuracy across all flow rates
3Measurement precision
If multi-point calibration techniques are used, then different infusion rates can be measured, but calibration remains inconsistent and unstable due to various factors
Solution Approach 1:
The patent implements a self-calibrating system that uses the pump's own mechanical compression characteristics to establish measurement reference points. The capacitive sensor automatically detects the relationship between line compression, fluid displacement, and capacitance changes during normal pump operation, eliminating the need for external calibration equipment and procedures while maintaining consistent measurements across different infusion sets and conditions
4Measurement precision
If conventional flowmeters are used, then flow measurement is possible, but accuracy degrades quickly when flow rate is far from calibration point
Solution Approach 1:
The patent implements a feedback mechanism where the capacitive sensor continuously monitors fluid presence and flow characteristics during pump operation. The system uses real-time capacitance measurements from multiple points in the compression cycle to continuously update and maintain measurement accuracy, providing feedback that compensates for deviations from calibration conditions and maintains precision across varying flow rates
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 system provides accurate flow measurement across a wide range of flow rates, is contamination-resistant, cost-effective, and operates under closed-loop control, reducing the need for frequent calibrations and maintenance.
Implementation Method 1
measure, during the cam motion, a first capacitance between the conductive plate and a conductor opposite the flexible infusion line; determine, based on the measured first capacitance, a volume of the fluid within the flexible infusion line
Data Source
AI summary
An integrated capacitive flowmeter for an infusion pump is disclosed. A conductive plate is attached to a hammer element that moves according to a cam motion in a pumping mechanism of the pump to periodically compress an flexible infusion line loaded in the pumping mechanism. A processor measures a first capacitance between the conductive plate coupled to the hammer element and a conductor opposite the flexible infusion line when the flexible infusion line is loaded between the conductive plate and the conductor in the pumping mechanism. A volume of the fluid within the flexible infusion line during the filling phase is then determined based on the measured capacitance, and a flow rate determined based on the determined volume and a cycle speed of the pump. The speed of the pump can then be adjusted based on a difference between the determined flow rate and a programmed flow rate.