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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 laboratory-quality 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.


Calculate Compensation Factor

Water displacement determined Sample Container volume to be 904cc
As we discuss density in lb/ft3, we will need to convert cc to ft3:
904cc (0.00003531cc/ft3) = 0.03192 ft3

Calculate Compensation Factor (i.e. how many sample containers required to total 1.0ft3?)
1ft3 = (X)0.03192 ft3
X = 31.328 ft3

- 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.


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 ft3(1.050 lb) = 32.9 lb/ft3

Please feel free to give Monitor Technologies a call (800-601-6319) or e-mail ( and let us put our creative solutions to work for you!




Spotlight: RF Capacitance Level Sensor
TrueCap Level SensorsTrueCap Light  
TrueCap® MK-2
Advanced RF Capacitance Level Probe

The TrueCap® Model MK-2 RF Capacitance point level probe is designed to provide a superior and stable sensitivity threshold making it suitable for a variety of powder / bulk solids and some liquid or slurry applications.

Advanced features of the Model MK-2 include:
> Automatic immunity to material build-up on the probe by its driven shield design
> Push-button calibration
> Enhanced temperature compensation
> Maximized reliability via smart sensing algorithms like “self-validating” fail-safe protection
> Visible status LED on ordinary location units
> Versatility through a variety of configuration options including: hazardous location version, split architecture design, quick-connect process connection, stub probe, cable extensions, solid extensions, Nylon® probes, Ryton® - equiv. probes, etc.

A practical application for the TrueCap would be to use this level sensor where a residual material build-up on a different sensor would cause a false material level indication.

Principle of Operation for the TrueCap RF Capacitance Level Probe:
The vessel wall and the active probe element establish an impedance reference between each other when exposed to air which has a dielectric constant of 1. When materials with a dielectric constant greater than 1 are in close proximity to the probe, the impedance of the sensing field between the sensor and the vessel wall will change. Once the amount of change exceeds a threshold that was electronically determined during the calibration process, an output relay will either be energized or de-energized depending upon the position of the fail-safe selector on the probe’s electronic circuit board. A change of as little as .5 pico-farad is all that is necessary for the probe to sense the presence of material.

Click here for more information on the TrueCap MK-2 Level Sensor or contact Monitor Technologies LLC at
Tel.: 800-766-6486 in the USA and
Tel.: 630-365-9403 worldwide.


>>Download TrueCap Product Bulletin #413

>>Click here to learn more about other Point Level Switches from Monitor Technologies


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