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Past and present trends in weighing technology

Posted: 14 Nov 2012 ?? ?Print Version ?Bookmark and Share

Keywords:flow meters? weigh feeders? PLC modules?

The weighing landscape is vast, with devices including solids flow meters, weigh feeders, PLC modules, and more. This article takes a look at the past and todayhow products have changed, markets have expanded, and the approval process has become more challenging.

The world of weighing is vast, with devices including solids flow meters, weigh feeders, PLC modules, load cells, belt scales and continuous weighing integrators. This article takes a look at the past and todayhow products have changed, markets have expanded, and the approval process has become more challenging.

Why weigh?
Every industry uses weighing in one way or another. Industrial uses include static weighing, where material does not move as it is weighed by load cells, and dynamic weighing, where material is weighed in motion either by belt scale, weigh feeder, or solids flow meter. A few examples:

In the mining, aggregates and cement industry: belt scales are used for custody transfer as material is sold by weight; weigh feeders control the flow of raw material for recipe blending; belt scales monitor the amount of material being added to stockpiles. In the chemical industry: load cells support bins or hoppers to indicate material level for filling and dosing. In the food and beverage industry: solids flow meters indicate the amount of material added to a mixture. In the water/wastewater industry: weigh feeders control the rate of additives during water purification.

Selecting a weighing system
There are many different weighing solutions based on application requirements. Belt scales are the easiest solution to find C anywhere there is a conveyor belt transporting material, may be a belt scale. If there is moving material and a need to know its rate or speed on the conveyor, a belt scale is the answer.

Weigh feeders are a bit more complex than a belt scale in that they also control the flow of the material. A weigh feeder is a complete weighing solution designed for weighing accuracy and repeatability. Typically, weigh feeders are used to introduce materials into a process out of a bin or hopper.

Solids flow meters, in comparison, can be more of a challenge to apply. They are used where material falls from one process to another by gravity. The key here is falling material. The solids flow meters are placed in pipe and duct systems to indicate flow rates and totalise material flow.

Check weighers monitor the weight of a product to ensure it meets quality or production standards. Platform scales are used for inventory control. Dosing and batching machines ensure that materials are mixed at the right proportions to make food as delicious as possible. These are most of the weighing technology you will find in today's automation plants worldwide. But how did some of these technologies evolve? And what are a few real-world applications?

That was then...
Forty years ago, belt scale demand came largely from North America. This market had long-established industries that were well suited for belt scale applications. Conveyors were built to Conveyor Equipment Manufacturers Association (CEMA) standards and the goal was clear: target the mining, aggregate, and cement business, otherwise known as the "heavy" industries.

Over time, other industries such as food and beverage, chemical, water/wastewater, and more, joined heavy industries in importance. Those industries brought new lists of requirements, which were difficult to meet with products focused on "heavy" industries. From a single belt scale offering all those years ago, Siemens, for example now has eight different versions of belt scales to meet applications: from food-grade wash down to 12,000 tph (13,220 stph) flow rates to hazardous environments.

Solids flow meters
Simply put, solids flow meters monitor the rate of bulk material flow in a process. They continuously measure the impact force of the material under gravity feed conditions and convert this signal into a flow rate used to control the material into a process or blending operation.

Over the years, solids flow meter options have expanded: different products for different applications, different materials of construction for material compatibility, ASME and DIN flanges. All of this adds up to more options, more info, and more solids flow meter applications.

Typical applications include:

???Cement
???Mineral
???Plastics
???Food processing
With the introduction of new flow meter models, these traditional applications have expanded, For example:

The design of a finish mill most commonly consists of a very large diameter steel tube filled with a designated quantity of steel grinding balls. As the mill is rotated at an optimum rpm (revolutions per minute), the grinding balls crush the clinker/gypsum mixture into a fine powder. For peak efficiency, the mill should run with an optimum load. Acoustic sensors may be used to measure the frequency of noise coming from the mill, as there is a relationship between the frequency and amplitude of the sound generated and the loading of the mill. This reading must be instantaneous and not disrupt the material flow.

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