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METTLER TOLEDO Weigh Module Systems Handbook

(12/99)3-2

Static versus Dynamic

METTLER TOLEDO offers five types of compression systems: Flexmount®, Flexmount

HD™, Centerlign™, Ultramount™, and Value Line weigh modules. Which type should

be used for an application depends on how the load will be applied. Flexmount,

Flexmount HD, and Value Line weigh modules are designed primarily for

static

applications, where minimal lateral forces are present (see Chapters 6, 7, and 10).

Most tanks and hoppers are static loading applications. Centerlign weigh modules are

designed for

dynamic

loading applications, where the weighbridge is subject to high

horizontal shear forces (see Chapter 8). Dynamic loading applications include

conveyors, pipe racks, mixers, and blenders. Ultramount weigh modules are designed

for smaller capacities (up to 100 kg per support point). They can be supplied with a

load pin for static loading applications or with a ball-and-cup assembly for dynamic

loading applications (see Chapter 9).

METTLER TOLEDO also offers Tension weigh modules for applications that require a tank

or other structure to be suspended. These weigh modules are designed for static loading

applications, where there is no side loading (see Chapter 11).

How Many Load Cells?

For an existing installation, the number of weigh modules is determined by the number

of existing supports. If a tank has four legs, you will need to use four weigh modules.

For a new installation, a three-point support system is inherently more stable and

accurate than a four-point support system. If wind, fluid sloshing, or seismic loading is

a factor, the tank might require four supports for additional protection against tipping.

Most tank scale applications use either three or four weigh modules. A METTLER

TOLEDO indicator can sum as many as eight weigh modules, although the weight

distribution and shift adjust would probably be less than ideal.

To calculate the required capacity for each weigh module, divide the gross capacity of

the system by the number of supports. A safety factor should be applied to the gross

capacity in case the weight is underestimated or distributed unevenly. The procedure for

sizing weigh modules is explained in the chapters about the individual types of weigh

modules (Chapters 6 to 11). Environmental factors such as wind loading can also

affect the capacity of the weigh modules required for an application (see Chapter 4).

Field Calibration

Another consideration is how the weigh module system will be calibrated. If you are

adding weigh modules to an existing tank, you might need to modify the tank so that

you can hang certified test weights from it. At a minimum, the tank should be able to

support test weights equal to 20% of the net product weight (programmed capacity).

Several methods of field calibration are described in Chapter 12.

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