

Determining the bulk density of a material to improve accuracy
of material weight calculation
In
the event that an accurate weight calculation is desired,
it will be critical to first know the exact bulk density of the target
material. (An accurate weight calculation is useful when implementing
a continuous
level measurement / inventory management system.)
The bulk density of any given material will vary from delivery to delivery
even if the same grade / specification of material is purchased. Some
suppliers will not say this, but reality will prove otherwise. A program
of sample weighing should be implemented to determine actual bulk density.
To Determine the Bulk Density of a Material:

Construct a sample container. This container can be of any
shape or size and should be made of dimensionally stable material (i.e.
not cardboard).
 Measure the volume of a sample container. This volume
measurement must be very accurate. Do not rely on measurements obtained
by a ruler or caliper as these are typically not of sufficient accuracy.
Rather, it is best to measure the sampling container volume by water
displacement method.
Obtain a graduated cylinder or other laboratoryquality calibrated
liquid dispensing vessel. Record the volume of liquid required to fill
the sampling container.
 Calculate Compensation
Factor. Bulk density
is most frequently measured in pounds per cubic foot. Chances of
obtaining a sample container that measures exactly one cubic foot
is near impossible. Consequently, it will be necessary to calculate
a compensating factor to allow precisely one cubic foot volume
to be ascertained.
Example:

Water displacement determined Sample Container
volume to be 904cc
As we discuss density in lb/ft^{3}, we will need to convert cc to
ft^{3}:
904cc (0.00003531cc/ft^{3}) = 0.03192 ft^{3} 
Calculate Compensation Factor (i.e. how many sample containers
required to total 1.0ft^{3}?)
1ft^{3} = (X)0.03192 ft^{3}
X = 31.328 ft^{3} 
 Weight the sample
of material. Use of an
accurate scale is imperative. Postal scales are convenient, accurate,
and almost all offices have such. Be sure to subtract the weight
of the sampling container from the overall measured weight.
 Apply Compensation Factor to determine bulk
density.
Example:
Total Sample Container with Sample:
Sample Container (empty):
Material only Weight: 
1.275 lb
0.225 lb
1.050 lb 
Apply Compensation Factor: 31.328 ft^{3}(1.050
lb) = 32.9 lb/ft^{3}
Please feel free to give Monitor Technologies
a call (8006016319) or email (monitor@monitortech.com) and let us
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