Inductive Conductivity Input Circuit with Direct Coupling
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Solution Overview
Problem
Existing inductive conductivity measurement circuits face challenges with low precision, complexity, and high costs, along with difficulties in detecting open-circuit failures in coils and cables, which affect the reliability and adaptability of conductivity measurements across different ranges.
Innovation Solution
A simplified input circuit design featuring two feedback loops with stable components like resistors and operational amplifiers, allowing direct compensation of DC offsets and enabling detection of open-circuit failures through a DC test current and voltage level detection, without the need for complex components or calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current-compensation method with feedback circuit is used to increase measurement precision, then measurement precision is improved, but device complexity increases due to many complex and expensive components
Solution Approach 1:
The patent extracts and eliminates complex components (tuned filter amplifier, in-phase detector, switching multiplier, numerous amplifiers) from the measurement circuit while retaining the essential feedback compensation functionality through a simplified operational amplifier-based circuit configuration
Solution Approach 2:
The patent replaces complex electronic component assemblies with a simplified operational amplifier circuit that achieves the same current compensation and feedback control functions through fewer, more integrated electronic elements
2Measurement precision
If complex components like tuned filter amplifier and in-phase detector are used to achieve high precision, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive, complex components with more affordable operational amplifiers and basic passive components (resistors, capacitors) that achieve comparable measurement precision at lower cost
Solution Approach 2:
The patent changes the circuit configuration parameters by using operational amplifiers with feedback networks instead of complex tuned filters and detectors, maintaining precision while reducing component cost
3Object-generated harmful factors
If DC-blocking capacitor is used to separate induction coil from operational amplifier, then DC offset is eliminated, but measurement precision deteriorates due to AC current attenuation
Solution Approach 1:
The patent removes the DC-blocking capacitor from the circuit by implementing direct coupling between the induction coil and operational amplifier, then eliminates DC offset through a different mechanism (feedback circuit with virtual ground)
Solution Approach 2:
The patent introduces a feedback circuit with virtual ground as an intermediary mechanism that eliminates DC offset without blocking AC signal transmission, replacing the capacitor's DC-blocking function with an active electronic solution
4Productivity
If conventional measurement circuits are used, then basic measurement function is achieved, but reliability is reduced due to inability to detect open-circuit failures
Solution Approach 1:
The patent incorporates a DC test current source that continuously monitors coil and cable integrity before and during measurements, detecting open-circuit failures in advance or in real-time
Solution Approach 2:
The patent uses feedback through the operational amplifier's virtual ground configuration to detect changes in circuit impedance that indicate open-circuit failures in coils or cables, providing continuous reliability monitoring
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 design achieves high accuracy, reliability, and adaptability in conductivity measurements, particularly at low conductivity levels, while being cost-effective and capable of detecting sensor failures, thus enhancing the measurement process.
Implementation Method 1
By supplying an alternating current to the excitation coil an alternating magnetic flux is generated in the magnetic ring carrying the excitation coil, which, in turn, generates an induction current through the loop in the measured liquid
Implementation Method 2
The induction current generated in the loop represents the current loop which passes through both the excitation-side magnetic ring and the pickup-side magnetic ring. This current loop generates an AC magnetic flux in the magnetic ring, which generates in the induction coil an induced current, which in turn produces an induced electrical voltage at the induction coil
Data Source
Figure 1
AI summary
The present invention discloses an input circuit for electromagnetic (inductive) measurements of the conductivity of liquids. The input circuit and the induction coil are directly coupled, and the arrangement includes a current-voltage converting circuit which accomplishes the transformation from current to voltage in the induction coil, and ensures the terminal voltage to be zero. Also there is an anti-saturation circuit which is composed of an integrating circuit and a voltage dividing circuit and serves to prevent saturation in the operational amplifier which is used for the current-voltage transformation. The circuit further includes features for the detection of an open-circuit failure of the sensor coil or cable. As a result, the present circuit is distinguished by high precision, low cost and good reliability.