Electromagnetic Flowmeter Shield Case for Noise Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitance-type electromagnetic flowmeters face issues with measurement accuracy and stability due to noise entry in wiring between the signal amplification circuit and electrodes, leading to signal attenuation and common-mode noise problems.
Innovation Solution
The electromagnetic flowmeter design includes a preamplifier circuit with operational amplifiers sealed in a single IC package, a subtracter circuit, and a shield case to surround the amplifiers and electrodes, with a differential amplification circuit configuration that sets the amplification factor greater than 1 to improve common-mode rejection ratio and suppress common-mode noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If capacitance-type electromagnetic flowmeters are configured with non-contact electrodes, then electrode durability and ease of maintenance are improved, but measurement accuracy and stability deteriorate due to high impedance and noise entry
Solution Approach 1:
A shield case is introduced as an intermediary component between the electrodes and the external environment. The shield case surrounds the electrodes and signal wiring, acting as a barrier that blocks noise from entering the high-impedance signal paths, thereby improving measurement accuracy while maintaining the non-contact electrode configuration
Solution Approach 2:
The patent converts the harmful effect of high impedance (which makes the system susceptible to noise) into a benefit by using the shield case to create a controlled electromagnetic environment. The shield case transforms the vulnerable high-impedance configuration into a noise-resistant system by providing electromagnetic shielding
2Object-affected harmful factors
If shielded cables are used to connect electrodes to the signal amplification circuit, then noise entry is reduced, but signal attenuation increases due to capacitance between core wire and shield conductor
Solution Approach 1:
The shield case serves as an intermediary that provides electromagnetic shielding without requiring long shielded cables. By placing the shield case close to the electrodes and signal circuitry, the patent reduces the length of signal paths while maintaining noise protection, thereby minimizing signal attenuation caused by cable capacitance
3Measurement precision
If preamplifiers are connected between detection electrodes and differential amplification circuit, then signal attenuation in shielded cables is reduced, but device complexity and production cost increase
Solution Approach 1:
The patent combines the shield case with the existing housing structure of the flowmeter, merging two functions (shielding and structural support) into a single integrated component. This approach provides noise protection without adding separate preamplifier stages, thereby maintaining signal quality while avoiding increased device complexity and production cost
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 configuration enhances the accuracy and stability of flow rate measurements by effectively removing common-mode noise and reducing the impact of noise and temperature variations, while also simplifying the shield case design and reducing production costs.
Implementation Method 1
an exciting coil (Lex) and a pair of electrodes (Ea, Eb). The exciting coil generates a magnetic field in a direction perpendicular to a direction in which a fluid flows in a measurement pipe
Implementation Method 2
In the capacitance-type electromagnetic flowmeters, instead of bringing the electrodes disposed at the measurement pipe to be in contact with a measurement-target fluid, an electromotive force generated by the measurement-target fluid is detected based on capacitances formed between the measurement-target fluid and the electrodes
Data Source
AI summary
An electromagnetic flowmeter includes a board having a preamplifier circuit and a shield case mounted thereon. The preamplifier circuit amplifies an electromotive force generated between first and second electrodes disposed to be perpendicular to a magnetic field generated by an exciting coil on a measurement pipe. The preamplifier circuit includes first and second operational amplifiers, a first wiring connecting the first electrode and a non-inverting input terminal of the first operational amplifier, a second wiring connecting the second electrode and a non-inverting input terminal of the second operational amplifier, a first resistor connecting an output terminal and an inverting input terminal of the first operational amplifier, a second resistor connecting an output terminal and an inverting input terminal of the second operational amplifier, and a third resistor connecting the inverting terminals of the first and second operational amplifiers.