ISFET Probe In-Situ Reference Electrode Diagnosis

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Solution Overview

Problem

Existing pH-measuring probes, particularly those using glass electrodes, face issues with bio-fouling, fragility, and the need for additional components that generate heat, making them unsuitable for certain industries like biopharmaceuticals and food processing, where reliable and heat-free diagnostics are crucial.

Innovation Solution

An ISFET measuring probe with a measurement circuit that includes an auxiliary electrode and an operational amplifier, allowing for in-situ diagnosis of the reference electrode's condition without removing the probe from the measurement medium, using a minimal number of components and reducing electrical current consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If glass electrodes are used for pH measurement, then measurement capability is achieved, but the electrodes are fragile and generate heat from diagnostic circuits

Engineering Contradiction:

Improvemechanical stabilityVSAvoidheat generation and fragility

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent replaces the mechanical glass electrode system with an ISFET-based measuring probe that uses field effect transistor technology. This substitution eliminates the fragility of glass electrodes while maintaining pH measurement capability through electrochemical detection at the ISFET gate, thereby removing the harmful mechanical and thermal issues associated with glass electrodes.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If additional diagnostic components are added to monitor diaphragm condition, then measurement accuracy is improved, but heat generation increases and device complexity increases

Engineering Contradiction:

Improvediaphragm condition monitoringVSAvoidnumber of additional components

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent implements self-service diagnostics by utilizing the ISFET device itself and existing circuit elements to monitor diaphragm condition. The measuring probe performs self-diagnosis by analyzing electrical characteristics during normal operation, eliminating the need for separate diagnostic components and reducing device complexity while maintaining measurement precision.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent makes existing circuit components multi-functional by using them for both measurement and diagnostic purposes. The same electrical paths and components used for pH measurement are also utilized to assess diaphragm condition, thereby avoiding additional components and reducing overall device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If the probe is removed from measurement medium for diagnosis, then accurate diagnosis can be performed, but measurement time is lost and productivity decreases

Engineering Contradiction:

Improvediagnosis accuracyVSAvoidmeasurement time

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent enables continuous operation by performing diagnostics in-situ within the measurement medium without removing the probe. The measuring probe continuously monitors both pH values and diaphragm condition simultaneously, ensuring uninterrupted measurement and maintaining high productivity while achieving accurate diagnosis through real-time electrical characteristic analysis.

Inventive Principle:

Principle #20Continuity of useful action

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 reliable, heat-free, and cost-effective in-situ diagnosis of the reference electrode's condition, maintaining measurement accuracy and safety by avoiding the need for additional components and minimizing probe removal, suitable for industries where glass electrodes are not preferred.

Implementation Method 1

According to Nernst's equation, a surface potential which depends on the ion concentration in the measurement medium establishes itself in the contact area between the measurement medium and the ion-sensitive layer at the gate of the ISFET

Methodology Applied

Scientific EffectNernst's equation:

Implementation Method 2

In a diagnostic mode, the auxiliary electrode is connected by way of a load resistor to a test voltage in order to measure a first time profile of the voltage on the reference electrode and/or a first time profile of the voltage on the auxiliary electrode

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS10197528B2ISFET measuring probe, measurement circuit for the ISFET measuring probe, and method

Publication Date: 2019.02.05 METTLER TOLEDO GMBH

AI summary

ISFET measuring probe with a housing in which an ISFET and a reference electrode are arranged in such a way that the gate electrode of the ISFET, which is coated with an ion-sensitive layer, and the reference electrode reach into a measurement space into which a measurement medium can be introduced, with the distinguishing feature that an auxiliary electrode is arranged additionally inside the housing and is held inside the measurement space.