Better Magnetic Flow Meter Sensors Increase Productivity

Based on many plant visits and discussions with Emerson customers, I have concluded that handling slurries is one of the biggest problems for operators and reliability teams. The most frequently mentioned issues are clogging and erosion, which certainly take their toll, but there is also a more subtle challenge related to measuring flow.

Why slurries cause this problem and what companies can do about it are the main point of my article in the January-February issue of Control Engineering, Better Magnetic Flow Meter Sensors Increase Productivity, Cut Downtime. The situation isn’t all that difficult to solve when using a flow meter technology designed especially to handle the effects of slurries.

Magnetic flow meters (aka, magmeters) are popular for slurry applications because they have no internal obstructions, no impulse lines, and they work well with water-based solutions, which matches most slurries. But not all magmeters are created equal.

Unstable and inaccurate magmeter readings often occur due to entrained debris in the fluid impacting the electrode sensors and causing millivolt spikes, which are then interpreted as flow spikes. Fiberglass pipe is often used in brine or chemical services, and it tends to create a lot of static current in the application, which like the particle impingement problem, affects measurement integrity. When using a standard magmeter, these noise signals measured by the electrodes struggle to separate from the flow signal consistently and accurately.


So, all those little particles banging around in the fluid can cause many types of mischief. If the flow reading is destabilized, other equipment involved in that part of the process can struggle to compensate, so operators may try to create workarounds to minimize the effects, but these create a different set of problems.

The traditional method of compensation for this type of noise is extending dampening time of the flow signal, which is done in the transmitter. Due to the nature of these slurry signals, it is not unusual to see damping times of 30 to 60 seconds. This technique produces a stable flow rate value, but it is not good for real-time control. For many flow processes, the process deadtime is often less than one second, so damping to this large an extent means control is responding to a change that occurred multiple cycles earlier, which can lead to unstable operation of the control system.

The better approach is to use a magmeter that is more resistant to the basic problem. Emerson’s Rosemount 8782 Transmitter for Slurry Applications can be paired with multiple Rosemount Magnetic Flow Meter sensors covering a range of sizes and configurations. Incorporating Emerson’s latest advanced signal processing, the 8782 is able to stabilize noisy process flow signals without having to compromise on responsiveness, and the ability to control a flow loop automatically.

Using this type of cutting-edge technology in a configurable and customizable manner provides low variability of flow readings, empowering personnel to run their plants closer to operating limits. It also provides improved automatic closed-loop control, better process stability, and increased throughput—along with less equipment wear and tear across a wide range of flow regimes, profiles, and ranges.

Visit the Emerson Flow Measurement pages at You can also connect and interact with other engineers in the Chemical Processing and Pulp & Paper Groups at the Emerson Exchange 365 community.

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