Excitation Circuit for Electromagnetic Flow Meter
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Solution Overview
Problem
Existing electromagnetic flow meters face challenges in achieving both high measurement stability and reduced size, as they often require increased excitation frequency and current, which leads to heat generation and complexity in the drive circuit, making it difficult to balance measurement accuracy with device compactness.
Innovation Solution
The proposed excitation circuit uses a configuration with separate control mechanisms for switching the excitation polarity and constant current control, employing two direct-current voltages and switching control circuits to manage the excitation current, allowing for direct pulse-driving of the excitation coil and reducing the need for a radiator, thus enhancing measurement stability and size reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the excitation frequency is increased to reduce 1/f noise and improve measurement stability, then the signal-to-noise ratio is enhanced, but the excitation current rises over a longer period due to self-inductance, reducing the steady-state period and making stable sampling difficult
Solution Approach 1:
The patent applies preliminary action by pre-charging a capacitor during a first time period before the excitation pulse is applied. This stored charge is then utilized during the excitation period to maintain constant current flow through the excitation coil, eliminating the gradual current rise that normally occurs due to self-inductance and ensuring immediate steady-state operation from the start of excitation.
2Measurement precision
If the excitation current is increased to increase the signal level of the flow rate signal, then the measurement stability is improved, but the heat generation of the power transistor increases, requiring a large radiator
Solution Approach 1:
The patent implements periodic action by cycling between two distinct operational modes: a charging period where energy is stored in a capacitor, and an excitation period where this stored energy is rapidly discharged through the excitation coil. This periodic charging and discharging enables high excitation currents to be achieved without continuous power dissipation, significantly reducing heat generation compared to sustained high-current operation.
Solution Approach 2:
The patent applies discarding and recovering by capturing and storing the electrical energy in a capacitor during the charging phase, then recovering and utilizing this stored energy during the excitation phase. This energy recovery mechanism eliminates the need for continuous power supply during excitation, reducing overall power consumption and heat generation while maintaining high signal levels.
3Measurement precision
If two power supplies with different voltages are used to make the excitation current rise rapidly at increased excitation frequencies, then the measurement stability is improved, but the device complexity increases
Solution Approach 1:
The patent applies dynamics by using a single power supply that dynamically switches between two operational states through electronic control: a charging state where the power supply charges a capacitor, and an excitation state where the capacitor discharges through the excitation coil. This dynamic switching mechanism replaces the need for two separate power supplies with fixed voltages, achieving rapid current rise while simplifying the overall power supply architecture.
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 solution enables a small electromagnetic flow meter with improved measurement stability by eliminating the need for a radiator and simplifying the drive circuit, allowing for increased excitation voltage and current without significant heat generation, thereby enhancing the signal level and frequency of the flow rate signal.
Implementation Method 1
an excitation coil for generating a magnetic field in a direction perpendicular to a direction of fluid flow within a measuring pipe
Implementation Method 2
measuring the flow rate of a fluid flowing in the measuring pipe by detecting an electromotive force generated between the electrodes
Data Source
AI summary
An excitation circuit includes a first switch connected between a third signal line and a first signal line supplied with a first DC voltage, a second switch connected between the third signal line and a second signal line supplied with a second DC voltage higher than the first DC voltage, third to sixth switches that reverses a polarity of a voltage on the third signal line to change a direction of an excitation current, a switching control circuit that switches the first switch at intervals shorter than intervals at which an excitation polarity is switched so that the excitation current has a first target value, and a switching control circuit that turns on the second switch when the absolute value of the excitation current is smaller than a second target value less than or equal to the first target value and that turns off the second switch when the excitation current is larger than the second target value.