Magnetic Flowmeter Current Sampling Circuit Impedance Mismatch

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Solution Overview

Problem

Conventional magnetic flowmeters face accuracy issues due to impedance mismatches in transmission lines, leading to voltage/current wave reflections and standing waves, which affect the accuracy of current generator current samples and the magnetic field generated, thereby impacting flow rate measurements.

Innovation Solution

The magnetic flowmeter incorporates a power amplifier with a low pass filter and a controller that adjusts the relationship between sampling frequency and current pulses, synchronizing or desynchronizing sampling points with remnant signals to minimize the impact of impedance mismatches, ensuring accurate coil current measurements and improved magnetic field control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of stationary object

If the transmission line is long to connect the current generator and sensor section, then the device can operate over longer distances, but impedance mismatch occurs causing voltage/current wave reflections and standing waves that reduce measurement accuracy

Engineering Contradiction:

Improvetransmission line lengthVSAvoidcurrent sample accuracy

Core Design Contradiction:

Length of stationary objectVSMeasurement precision

Solution Approach 1:

The patent implements a feedback mechanism where the current generator samples the coil current through the transmission line and uses this feedback information to adjust its output. The current generator includes a sampling circuit that measures the actual current reaching the coil and compares it with the desired current, then modifies its output to compensate for losses and reflections in the long transmission line, maintaining measurement accuracy despite the impedance mismatch.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the operating parameters by using pulsed current instead of continuous current, and by varying the pulse width and frequency to optimize the magnetic field generation. The current generator switches between different current levels and timing parameters to create the necessary magnetic field while minimizing the impact of transmission line effects on measurement accuracy.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If impedance mismatch is present in the transmission line, then the system can tolerate varying load conditions, but standing waves are generated that adversely affect current sampling accuracy

Engineering Contradiction:

Improveload condition toleranceVSAvoidcurrent measurement accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The current sampling circuit provides real-time feedback on the actual current reaching the coil, allowing the current generator to detect and compensate for standing wave effects. By continuously monitoring the current through the transmission line and adjusting its output accordingly, the system maintains accurate current measurements even when impedance mismatch causes standing waves.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent uses periodic pulsing of the current through the coil rather than continuous current flow. By applying current in controlled pulses and sampling at specific points in the pulse cycle, the system can distinguish between the desired current signal and the standing wave artifacts, improving measurement accuracy while maintaining adaptability to varying load conditions.

Inventive Principle:

Principle #19Periodic 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

This solution enhances the accuracy of flow rate measurements by effectively managing impedance mismatches, reducing errors caused by standing waves and ensuring the magnetic field meets operational parameters, thereby improving the precision of fluid flow measurements.

Implementation Method 1

a coil configured to receive a coil current and produce a magnetic field across the fluid flow that induces an EMF in the fluid flow that is proportional to the flow rate

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

The power amplifier includes a low pass filter that attenuates the unfiltered current pulses to form coil current pulses at a second frequency that form the coil current

Methodology Applied

Scientific EffectElectrical filtering: Filter (electronic)

Data Source

PatentUS11181404B2Magnetic flowmeter with a current sampling circuit sampling coil current pulses at a sampling frequency

Publication Date: 2021.11.23 MICRO MOTION INC

AI summary

A magnetic flowmeter includes a flow tube assembly, an electromotive force (EMF) sensor, a power amplifier, a current sampling circuit, and a controller. The flow tube assembly receives the fluid flow, and includes a coil configured to receive a coil current and induce an EMF in the fluid flow that is proportional to the flow rate. The EMF sensor generates an output indicating the induced EMF. The power amplifier is configured to generate unfiltered current pulses at a first frequency. The power amplifier includes a low pass filter that attenuates the unfiltered current pulses to form coil current pulses at a second frequency that form the coil current. The current sampling circuit samples the coil current pulses at a sampling frequency. The controller is configured to change a relationship between the sampling frequency and the first frequency, and adjust the coil current based on the samples.