Rice Lake BCi Belt Scale - Installation & Operation Manual Version 2.00 - Manual (Page 56)

50 BCi Installation & Operation Manual
Material Testing
Material testing is the only known way to establish repeatability and traceable accuracy of a conveyor belt scale
system. Normally three or more successive material tests are required to achieve acceptance accuracy and
demonstrate repeatability of the belt scale system. Once the material test is complete, one or more methods of
simulated testing is also done to ensure accuracy. Material tests should be done at least every six months.
Material tests should also be done immediately following any type of conveyor maintenance that may affect the
scale.
The test itself consists of passing previously weighed - or material to be weighed, over the belt conveyor scale.
Care must be taken to see that all material is weighed both on the reference scale and on the belt conveyor scale.
The two weights are compared, the differences figured, and the error is percentage computed.
The following steps are involved in doing a material test.
1. The reference scale (track scale, truck scale, dumper scale, hopper scale, etc) is checked to determine
that it is in compliance with the applicable regulatory agency or Handbook 44 and must not leak or be
overloaded to the point that material will be lost. According to Handbook 44 instructions, the test shall
not be less than 1000 scale divisions, must run at least three revolutions of the belt scale and must run for
at least 30 minutes or more (below 41
° F, the belt should be run longer).
2. After running the belt empty (to warm up the belt), a reading is taken from the integrator.
3. The belt is run for a period of time equal to that required to deliver the minimum totalized load,
approximately 10 minutes and the reading is again taken. It should not vary more than +/- increment of
the scale. If the reading varies more, the zero must be adjusted. This process is repeated until an
acceptable zero condition is achieved.
4. After taking the integrator reading, material is introduced onto the scale belt and the rate of flow should
be carefully watched to rise to better than 35% of the rated capacity. The ideal operating and weighing
range is 50 to 85% of the rated capacity. A rule of thumb is if the time the scale is operated under 35% of
rated capacity, after the infeed is opened and closed, doesn’t exceed 10% of the running time, acceptable
weighing is present.
5. After the weighing has been completed, the belt should be running and empty (do not stop the belt).
6. The reading is taken from the master totalizer again. The “start” figure is subtracted from the “stop”
figure, which shows tons (or pounds) weighed. This figure is compared with the printer. The printer may
show +/- increment difference.
7. Compute the percent error. If the belt conveyor scale is out of tolerance, adjust the span by the computed
error. Repeat the material test again, steps 4-6. If the scale is in tolerance, the accuracy is established; and
proceed to step 8. If not, compute the error and again, adjust the belt conveyor span. If the accuracy
tolerance cannot be obtained, determine the problem before proceeding.
8. Conduct a final material test following steps 4-7 (do not adjust the span). If the belt scale is in tolerance,
its repeatability is established. Note: on the initial verification, two additional test are required, total
three to establish repeatability.
There are several advantages and disadvantages to material testing. They are listed in the following table.
Advantages of Material Testing Disadvantages of Material Testing
This is the only method that can establish traceable
conveyor scale accuracy. Requires availability of accurate static scale.
It readily permits testing at several feed rates to test
linearity. Requires accumulation, transportation to static scales, and
static weighing of the test load material.
It tests the entire system; electronics, scale carriage, and
the conveyor effects.
Table 5-1. Advantages and Disadvantages to Material Testing