Ion-Sensitive Element Drift Suppression via Periodic Refresh
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Solution Overview
Problem
Measurement devices equipped with ion-sensitive elements, such as ISFETs, experience output variations due to drift over time, which is problematic for applications requiring continuous and accurate pH measurements over long periods, like soil monitoring.
Innovation Solution
Incorporating a reference electrode and a controller that alternates between a measurement state and a refresh state, where the potential difference between the ion-sensitive element and the reference electrode is greater in the refresh state, to reset the surface potential of the ion-sensitive film and suppress output variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous measurement is performed using an ion-sensitive element, then productivity is improved, but output precision deteriorates due to drift
Solution Approach 1:
The patent applies periodic action by alternating between measurement periods and refresh periods. During measurement periods, the ion-sensitive element performs continuous pH measurement. During refresh periods, the surface potential of the ion-sensitive film is reset by applying a larger potential difference. This periodic switching resolves the contradiction by maintaining measurement capability while periodically eliminating drift accumulation, thus preserving output precision over extended continuous operation.
2Duration of action of moving object
If measurement is performed over long periods, then productivity is improved, but measurement precision deteriorates due to drift
Solution Approach 1:
The patent implements periodic refresh cycles during which the surface potential of the ion-sensitive film is reset by applying a larger potential difference between the ion-sensitive element and reference electrode. This periodic action allows the system to maintain measurement capability over extended durations while periodically eliminating drift, thus resolving the contradiction between long measurement duration and maintained precision.
3Measurement precision
If the potential difference is increased to reset surface potential, then measurement precision is improved, but energy consumption increases
Solution Approach 1:
The patent applies the periodic action principle by implementing intermittent refresh cycles rather than continuous high potential difference application. The controller switches between measurement periods (normal operation) and refresh periods (higher potential difference applied). This periodic approach achieves the necessary surface potential reset for precision while minimizing energy consumption by limiting high-power operation to brief refresh intervals.
Solution Approach 2:
The patent applies partial action by providing the larger potential difference only during specific refresh periods when surface potential reset is needed, rather than continuously. This partial application of excessive potential difference achieves the required precision correction while minimizing overall energy consumption compared to continuous high-power operation.
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 effectively moderates the effects of drift, allowing for continuous and accurate pH measurements over extended periods without significant output voltage variations.
Implementation Method 1
a measurement device equipped with an ion-sensitive element outputs electronic signals representing a hydrogen ion index (below referred to as the pH value)
Implementation Method 2
a reference electrode disposed in a state in which a measurement subject is interposed between the reference electrode and the ion-sensitive element
Implementation Method 3
establishing a second state within each period after the first state has been established and before the first state is next established, the second state being a state in which a potential difference between the ion-sensitive element and the reference electrode is greater than a potential difference between the ion-sensitive element and the reference electrode in the first state
Data Source
AI summary
A measurement device including: an ion-sensitive element; a reference electrode disposed in a state in which a measurement subject is interposed between the reference electrode and the ion-sensitive element; and a controller configured to: establish a first state at a predetermined interval, the first state being a state in which a current flows at the ion-sensitive element, and establish a second state within each period after the first state has been established and before the first state is next established, the second state being a state in which a potential difference between the ion-sensitive element and the reference electrode is greater than a potential difference between the ion-sensitive element and the reference electrode in the first state.