High-precision Electromagnetic Flowmeter with Empty Pipe Detection via Complex Programmable Logic Device-based Waveform Recognition

Summary

This study improves electromagnetic flowmeter accuracy by optimizing excitation waveforms, applying multi-stage filtering, and using Complex Programmable Logic Device (CPLD)-based rectification. A novel waveform-based empty pipe detection method enhances reliability. Experiments show 0.1% accuracy within 0.1-15 m/s, validating industrial applicability.

Abstract

Traditional electromagnetic flowmeters are inherently prone to external interference and uneven velocity distribution during measurement, which severely limits their accuracy. In this study, an improved method is proposed, which optimizes the excitation drive waveform, performs multiple filtering and amplification of the electrode input, and uses a Complex Programmable Logic Device to achieve rapid switching between positive and negative induction signals. This enables smooth rectification and, in combination with software filtering techniques, achieves highly precise performance. Additionally, empty pipe detection is realized by recognizing excitation waveform and input waveform patterns.

Experimental verification shows that the designed electromagnetic flowmeter achieves an accuracy of 0.1% within a flow velocity range of 0.1-15 m/s, with system repeatability errors of less than 1%. The results validate the effectiveness of the proposed method in high-precision flow measurement. The study demonstrates that high-precision detection can be achieved with minimal additional cost, which is important for industry applications.

Introduction

Electromagnetic flowmeters are flow measurement instruments that operate based on Faraday's law of electromagnetic induction. Compared with traditional mechanical flowmeters, electromagnetic flowmeters exhibit superior adaptability to various media and have lower requirements for straight pipe sections¹. When fluid passes through the pipeline, the electromagnetic flowmeter generates a magnetic field and measures the induced voltage difference in the fluid to calculate the flow velocity². Electromagnetic flowmeters are particularly suitable for complex environments like those in the chemical and petroleum industries

Protocol

1. Processing of electrode-induced voltage

1. Take the induced electromotive force from both sides of the sensor as the input signal (Figure 1A).
   ​NOTE: The original voltage signal is extremely weak and severely contaminated by noise, exhibiting a low signal-to-noise ratio (SNR).
2. Apply a 10x differential amplifier to amplify the signal (Figure 1B).
3. Proceed to feed the signal into an active second-order bandpass filter comprising cascaded high-pass and low-pass filter stages. Initially, remove low-frequency components through the high-pass filter, then channel the filtered out....

Results

To ensure standardized experimental conditions and the reliability of results, the experiment utilizes the hydraulic pump shown in Figure 4 to generate a stable standard water flow as the experimental environment. The water flow generated by this hydraulic pump can be approximated as a constant-velocity stream due to its stable power output characteristics, thereby meeting the experimental requirements for uniform fluid delivery. The standard instrument used .......

Discussion

There are various implementations of excitation waveforms in electromagnetic flowmeters, among which square wave excitation and step wave excitation are two commonly used types. Square wave excitation is widely adopted due to its simplicity in implementation¹⁵. However, this method is prone to inducing eddy current effects during the transient phase of excitation switching, which negatively impacts the stability of the measurement signal¹⁶. Additionally, the issue of zero-p.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Electromagnetic flowmeter	ABB	ABB-DN50	As a standard instrument, it is compared with the instrument in this article.
Electromagnetic flowmeter sensor	ABB	ABB-DN50	Used for collecting induced electromotive force.