Cracking the Code on Slurry Noise: Why Multi-Frequency Excitation is Essential for High-Consistency Pulp Measurement

or process engineers in Southeast Asian paper mills, maintaining a stable control loop is a constant battle against the physics of the fluid itself. With regional mills heavily utilizing recycled fiber and high-consistency eucalyptus pulp, traditional fluid measurement methods frequently fail.

The number one complaint from field engineers regarding pulp loops? Unstable flow meter readings.

The RBHEF-LS Slurry-Type Electromagnetic Flowmeter

This technical article breaks down why this happens and how Multi-Frequency Excitation Technology—as deployed in the RBHEF-LS Slurry Magmeter—solves it permanently.

The Root Cause: Electrochemical Slurry Noise

When a paper mill pumps pulp with a mass fraction of 10% to 11%, the fluid behaves less like water and more like an aggressive, semi-solid paste. Within this paste are millions of rigid cellulose fibers and microscopic debris.

As these solids flow past the flush-mounted electrodes of an electromagnetic flowmeter, they physically strike and scrape the metal surfaces. This friction triggers a chaotic chemical-electrical reaction on the electrode surface, generating high-amplitude, random voltage spikes. This is Slurry Noise.

[Legacy Low-Frequency Magmeter] 

Flow Signal + Severe Fiber Friction Noise ──> Transmitter Confusion ──> Erratic DCS Readings (±50% Fluctuation)

[RBHEF-LS Multi-Frequency Magmeter]

Flow Signal + Severe Fiber Friction Noise ──> Multi-Frequency Decoupling ──> Rock-Solid DCS Line (<±0.5% Drift)

Traditional magmeters utilize low-frequency square wave excitation (typically 6.25Hz to 25Hz). Unfortunately, the frequency of fiber friction noise falls directly into this same spectrum. The transmitter cannot distinguish the noise from the flow signal, leading to the erratic data jumps that disrupt automated PLC/DCS blending.

The Breakthrough: Multi-Frequency Spectrum Isolation

The RBHEF-LS Slurry-Type Electromagnetic Flowmeter solves this by replacing outdated single-frequency drives with a proprietary Multi-Frequency Excitation spectrum.

Technical Metric Standard Low-Frequency Magmeters RBHEF-LS Slurry Magmeter

Excitation Method Single low-frequency square wave Advanced Multi-Frequency Matrix

Signal-to-Noise Ratio (SNR) Poor in fluids >6% consistency Excellent in fluids up to 11–12% consistency

Zero-Point Stability Drifts under heavy slurry friction Ultra-stable due to algorithmic noise cancellation

DCS Output Signal Highly erratic (requires heavy dampening) Real-time, clean, and stable 4–20 mA / HART

By superimposing high-frequency components onto the magnetic field drive, the RBHEF-LS creates a multi-dimensional measurement baseline. The digital signal processor (DSP) inside the transmitter algorithmically isolates the chaotic, wideband slurry noise and discards it, processing only the true flow-induced electromotive force.

Real-World Validation

In a recent 500,000-ton/year recycled fiber pulping project, 28 units of the RBHEF-LS were installed on heavy-slurry lines. Previously, legacy meters on these lines suffered from constant data spiking, forcing operators to run the valves manually. Upon installing the multi-frequency RBHEF-LS meters, flow data fluctuations dropped to under ±0.5%, allowing the mill to run fully automated, optimized closed-loop dosing for the first time.