Optical Sensor Linearization via Bypass Mode Back-Extrapolation
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Solution Overview
Problem
Current methods for determining the Kt/V value during dialysis, such as online clearance measurement and optical sensing, face challenges due to non-linearity in optical sensors and the need for reference devices, leading to measurement uncertainty and underestimation of urea clearance, especially at high toxin loads.
Innovation Solution
A dialysis machine with a data correction device that linearizes the optical sensor by extrapolating data from a non-linear to a linear domain using shunt intervals and non-linear regression, allowing for extended linear measuring range without additional hardware and enabling accurate Kt/V calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical sensor is used to measure toxin concentration in dialysate, then measurement of dialysis effectiveness is enabled, but measurement precision deteriorates due to non-linear sensor response at high extinction values
Solution Approach 1:
The system performs preliminary actions by repeatedly switching to bypass mode during dialysis therapy to create measurement conditions that generate data points in the linear range of the optical sensor. This preliminary data collection enables subsequent back-extrapolation to correct non-linear measurements, thereby improving measurement precision without requiring hardware modifications.
Solution Approach 2:
The invention creates a virtual reference measurement by mathematically back-extrapolating from linear range measurements to estimate what the sensor reading would be in the non-linear range. This virtual reference curve serves as a correction model that copies the expected linear response, allowing accurate determination of clearance values even when direct measurements fall in the non-linear region.
2Measurement precision
If a reference device with wide linear measuring range is used, then measurement uncertainty is reduced, but device complexity increases
Solution Approach 1:
The optical sensor system performs self-service by using its own measurements in the linear range to generate a correction model that compensates for its non-linear behavior. The system creates its own virtual reference curve through back-extrapolation of its measured data, eliminating the need for external reference devices while maintaining measurement accuracy.
Solution Approach 2:
The invention changes the operational parameters of the optical sensor by repeatedly switching to bypass mode, which alters the flow conditions and creates opportunities to collect data in the linear measurement range. This parameter change enables the system to operate effectively despite the sensor's inherent non-linearity at high extinction values.
3Measurement precision
If bypass mode is repeatedly switched on during dialysis therapy, then linearization of optical sensor is achieved, but duration of action is reduced due to therapy interruption
Solution Approach 1:
The system implements periodic action by switching to bypass mode at regular intervals during dialysis therapy. These periodic bypass activations create repeated opportunities to collect linear range measurement data, which is then used to build and update the back-extrapolation correction model. The periodic nature ensures continuous improvement of linearization accuracy while minimizing overall therapy interruption.
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 approach reduces measurement uncertainty, optimizes Kt/V calculation, and allows for non-invasive determination of blood-side clearance values, even at high extinction levels, by extending the linear measuring range and correcting non-linear sensor data, thereby improving dialysis efficiency monitoring.
Implementation Method 1
The optical sensor 8 comprises at least one photodiode and preferably two photodetectors and is used to determine an absorption property of a dialysate. This preferably concerns the absorbance or extinction, which can be measured when the dialysate contains substances that absorb light.
Data Source
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AI summary
A method for linearizing an optical sensor in a dialysis device includes inserting a sensor into the dialysate-side drainage line, determining the linear range of the optical sensor, back-extrapolating the data from the linear range, and correcting the data from the non-linear range.