Glass Electrode Impedance Measurement With Variable Feedback
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Solution Overview
Problem
Conventional pH measurement apparatuses using glass electrodes face challenges in accurately measuring electrode impedance due to electrode deterioration, leading to reduced measurement accuracy and difficulties in maintaining multiple systems.
Innovation Solution
A measurement apparatus and method that includes a feedback resistor with a variable resistance value, operational amplifiers, and switches to adjust impedance measurement based on electrode conditions, allowing for precise impedance measurement and pH determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional impedance measurement methods are used, then the measurement can be performed with basic circuit components, but the measurement accuracy deteriorates when electrode impedance becomes extremely high
Solution Approach 1:
The feedback resistor is made variable rather than fixed, allowing its resistance value to be dynamically adjusted based on the electrode's impedance characteristics. This enables the measurement circuit to adapt to different impedance ranges, maintaining measurement accuracy even when electrode impedance becomes extremely high, while avoiding the need for multiple fixed resistor configurations
Solution Approach 2:
The resistance value of the feedback resistor is changed as a variable parameter to match the impedance level being measured. By adjusting this key circuit parameter, the measurement system can accurately handle a wide range of impedance values without requiring fundamentally different circuit topologies, thus improving measurement precision without proportionally increasing device complexity
2Measurement precision
If the feedback resistor resistance value is increased to measure high impedance electrodes, then measurement accuracy improves, but the circuit becomes more sensitive to noise and instability
Solution Approach 1:
The variable feedback resistor allows the circuit to dynamically select the appropriate resistance value based on the specific measurement requirements. When measuring high impedance electrodes, the resistor value can be increased to improve accuracy, while for lower impedance measurements, a lower resistance value maintains stability and reduces noise sensitivity, thus resolving the trade-off between precision and reliability
Solution Approach 2:
The operational amplifier with feedback resistor configuration provides negative feedback that stabilizes the measurement circuit. By carefully selecting and adjusting the feedback resistor value, the circuit maintains stability while being able to measure high impedance signals, as the feedback mechanism compensates for potential instability introduced by high resistance values
3Measurement precision
If separate measurement systems are used for pH measurement and impedance measurement, then each measurement can be optimized independently, but the overall system complexity and maintenance burden increase
Solution Approach 1:
The measurement apparatus is designed to perform multiple functions using a unified circuit architecture. The same operational amplifier-based measurement circuit can measure both pH (through potential difference) and impedance (through impedance analysis), eliminating the need for completely separate measurement systems. This multi-functionality reduces overall system complexity while maintaining measurement precision for both parameters
Solution Approach 2:
The pH measurement circuit and impedance measurement circuit are merged into a single integrated measurement system. By combining these functions in one apparatus with shared components like the operational amplifier and feedback resistor, the system achieves both measurement capabilities without the complexity and maintenance burden of completely separate systems, while still optimizing each measurement type
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, even at high impedance values, with the ability to detect electrode deterioration and predict replacement timing, enhancing measurement accuracy and system maintenance efficiency.
Implementation Method 1
When two different solutions are present on both sides of a special glass membrane, an electromotive force proportional to a difference in pH between the two solutions is generated in the glass membrane
Implementation Method 2
a feedback resistor that is a variable resistor having a third terminal connected to the output terminal, and a fourth terminal connected to the first input terminal
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
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.