Variable Feedback Resistance for Glass-Electrode Impedance Measurement
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Solution Overview
Problem
Conventional pH measurement apparatuses using glass electrodes face challenges in accurately measuring impedance due to electrode deterioration, leading to reduced measurement accuracy and difficulty in maintaining multiple systems.
Innovation Solution
A measurement apparatus and method that includes a feedback resistor as a variable resistor, operational amplifier, and switches to adjust resistance values based on electrode impedance, allowing for precise impedance measurement and pH determination, even with high impedance electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a glass electrode is used for pH measurement, then pH measurement capability is provided, but measurement accuracy deteriorates due to electrode deterioration and impedance variation
Solution Approach 1:
The system performs preliminary impedance measurement of the electrode before pH measurement to detect electrode deterioration in advance. By measuring impedance as a preliminary check, the system can identify electrode degradation trends and alert users before measurement accuracy is significantly compromised, thus maintaining reliable pH measurement capability.
Solution Approach 2:
The system continuously monitors electrode impedance and provides feedback about electrode condition. This feedback mechanism allows the system to track electrode deterioration over time, notify users when replacement is needed, and maintain measurement accuracy by ensuring the electrode is in acceptable condition before use.
2Measurement precision
If impedance measurement capability is added to the pH measurement apparatus, then electrode monitoring is improved, but device complexity increases
Solution Approach 1:
The impedance measurement function is merged with the existing pH measurement apparatus by utilizing the same operational amplifier and feedback resistor circuitry. The system combines both measurement capabilities in a single integrated device, sharing common components such as the operational amplifier, feedback resistor, and microcontroller, thereby avoiding the need for separate impedance measurement equipment and reducing overall system complexity.
Solution Approach 2:
The operational amplifier and feedback resistor circuit are designed to serve multiple functions: both pH measurement and impedance measurement. The same hardware infrastructure is used for dual purposes, making the apparatus multi-functional and reducing the need for additional dedicated components for impedance monitoring.
3Ease of manufacture
If a fixed resistance feedback resistor is used, then circuit simplicity is maintained, but measurement adaptability deteriorates for electrodes with varying impedance
Solution Approach 1:
The feedback resistor is changed from a fixed value to a variable/resistive network that can dynamically adjust its resistance. This dynamic adjustment capability allows the circuit to adapt to electrodes with different impedance values, ensuring accurate measurements across a wide range of electrode conditions while maintaining relatively simple circuit architecture through programmable control.
Solution Approach 2:
The resistance value of the feedback resistor is made changeable through a resistive network with multiple taps or switched resistor configuration. By changing the resistance parameter of the feedback element, the system can optimize the measurement range and maintain accuracy for electrodes with varying impedance characteristics without requiring completely different circuit designs.
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
Enables accurate and simple impedance measurement of glass electrodes, correcting for temperature and electrode deterioration, and predicting replacement timing, thereby enhancing measurement accuracy and system maintenance efficiency.
Implementation Method 1
measure the impedance of an electrode to be measured... based on a voltage applied to the second terminal, the potential of the output terminal, and a resistance value of the feedback resistor
Data Source
AI summary
The impedance of an electrode can be measured more simply and accurately, in a pH measurement apparatus using a glass electrode. A measurement apparatus (10) includes a measurement unit (161) that measures the impedance of an electrode to be measured having first and second terminals, and a controller (11). The measurement unit (161) includes an operational amplifier having first and second input terminals and an output terminal, and a feedback resistor, which is a variable resistor, having a third terminal connected to the output terminal, and a fourth terminal connected to the first input terminal. The controller (11) acquires, in a state of the first input terminal connected to the first terminal, a measurement value of the impedance of the electrode to be measured, based on a voltage applied to the second terminal, the potential of the output terminal, and a resistance value of the feedback resistor.