Multi Load Cells Apply to Variable Belt Scale with Three Measured Values

I. Working principle of variable belt scale with three-groups measured values
Taking the variable belt scale as an example whose full suspension scale rack is supported by four beam load cells, the belt scale divides four load cells into four independent signals which then enter the digital transmitter on site, the digital transmitter converts weighing analog signal into digital signal and convey it to the load cell controller. By grouping the four independent weighing signals respectively and combining the signal of speed load cell, the load cell controller would calculate the cumulative and instantaneous flow of three groups of feeding medium, namely one group of main value and two groups of auxiliary value.
The main value is produced by the full suspension belt scale rack which is supported by four beam load cells (see figure 1).

The other two groups of auxiliary value are respectively produced by single lever scale rack which is supported by load cells A and B (load cells C and D are used as pivot point at this time, see as figure 2).

And the single lever scale rack which is supported by load cells C and D (load cells A and B are used as pivot point at this time, see as figure 3).

The load cell controller displays the main value normally. As the two groups of auxiliary value are calibrated with the main value at a same time, the two groups of auxiliary value are compared online in real time. If there's a huge measurement difference that exceeds the setting range, then output signal of the load cells formed the two groups of auxiliary value would be compared respectively. The load cell whose errors exceed the setting range produces the faulted group of auxiliary value.
Meanwhile, the normal group of auxiliary value will be selected to replace the display of main value, thus ensuring that the belt scale can still weigh even when one load cell breaks or operates abnormally, improving the operation reliability and measurement accuracy of the belt scale.

II. Working principle of material feeder/coal feeder with three-groups measured values
Material feeder/coal feeder with three-groups measured values adopts two groups of full suspension type single roller scale rack (load cell AB and load cell CD), each group of full suspension type single roller scale rack is supported by two load cell modules, and two groups of full suspension type scale rack are supported by four load cells in total. Four load cells are divided into four independent signals to enter the digital transmitter on site, the digital load cell transmitter converts weighing analog signal into digital signal and convey it to the load cell instrument. By grouping the four independent weighing signals respectively and combining the signal of speed load cell, the load cell instrument would calculate the cumulative and instantaneous flow of three groups of feeding medium, namely one group of main value and two groups of auxiliary value.
For main value, two groups of single roller scale rack forms a double-roller scale rack which has a long weighing range and high measurement accuracy. When the belt scale works normally, the main value shows the measurement. For auxiliary value, it's composed of a group of single roller scale rack independently. Comparing the auxiliary value of each group of single roller scale rack obtained by software, if there's a huge measurement difference that exceeds the setting range, then load cells output signal of the single roller scale rack formed the two groups of auxiliary value would be compared respectively. The load cell whose errors exceed the setting range produces the faulted group of auxiliary value.
Meanwhile, the normal group of auxiliary value will be selected to replace the display of main value, thus ensuring that the weighing feeder/coal feeder can still weigh even when one load cell breaks, greatly improving the operation reliability and measurement accuracy of the weighing feeder/coal feeder while avoiding the economy losses caused by load cell fault and inaccurate measurement.

III. Application of Variable Belt Scale with Three Measured Values
The commercial variable belt scale with three-groups measured values is widely used in important fields, such as the wharf loading/unloading, coal mine loading, measurement of coal quality in power plant, and it has been well received by users due to its superior performance. In the application of a variable belt scale with three-groups measured values, users can not only find the fault of load cell timely in its operation, but also find out the abnormalities in load cells (material hopper at the scale rack, supporting deformation, structural change, bolt loosening). What's more, the belt scale can still weighs normally and the feeding system doesn't need to stop, thus avoiding the great economic loss caused by inaccurate measurement due to faults or abnormalities of load cells.
The test data of variable belt scale at site:

• Belt length: 99.475m
• Belt speed: 2.715m/s
• Belt width: 800mm
• Belt tilt angle: 16 degrees
• Conveying capacity: 500 ton/h

The belt scale rack adopts four-roller scale frame structure supported by four load cells, and the instrument adopts PLR 3 measured values load cell controller.
1. Zero point test:

Main value	Auxiliary value 1	Auxiliary value 2
0.000 ton	0.001 ton	-0.000 ton
0.002 ton	0.002 ton	-0.001 ton
0.001 ton	0.001 ton	-0.002 ton

2. Material test:

Material value	Main value	Auxiliary value 1	Auxiliary value 2
9.939 ton	9.944 ton	9.950 ton	9.939 ton
9.947 ton	9.948 ton	9.951 ton	9.945 ton
9.942 ton	9.945 ton	9.950 ton	9.940 ton

In a word, weighing technology of variable belt scale with three-groups measured values solves the long-term problem of belt scale, namely it's difficult to find out the faults of load cell, it also solve the influence of abnormal load cell on measurement, thus improving the reliability and measurement accuracy of belt scale and bringing convenience to the production management of all trades and professions, better meeting customers' needs.