Volumetric or gravimetric dosing: key points in 30 seconds
Technical summary:
To choose between volumetric and gravimetric dosing, you must first understand the actual behavior of the powder. Bulk density, its variability, and the production environment directly impact dosing accuracy.
Volumetric dosing consists of delivering a constant volume, generally by counting the number of screw rotations. It is fast and highly repeatable when the product is stable and the hopper level remains constant.
Gravimetric dosing measures the product weight directly and makes it possible to partially compensate for density variations. It is therefore more suitable when weight accuracy is critical or when the product varies.
Why compare volumetric and gravimetric dosing?
The choice between these two technologies is not limited to the machine itself. It directly impacts achievable accuracy, production rate, overall cost, the number of tooling configurations required, and the ability to monitor production.
In the context of industrial powder filling, this choice depends on several key parameters:
- powder behavior
- density variability
- target dose
- required throughput
- expected level of accuracy
- production environment
How do the two technologies work?
Volumetric dosing
Volumetric dosing is achieved by counting the number of screw rotations, or in some cases by timing. Each rotation corresponds to a fixed volume of product.
The resulting weight depends directly on the bulk density. If the density remains stable, repeatability is excellent. However, any variation in density leads to variations in weight.
Maintaining a constant product level in the hopper is essential to ensure stable dosing.
This method performs particularly well at high speeds and is generally well suited for doses below 1 kg.
It also allows the product to be compacted or compressed during filling without losing accuracy, as seen in certain applications such as talc filling.
Gravimetric dosing
Gravimetric dosing is based on direct weight measurement. The cycle typically involves two stages: a fast filling phase followed by a slower fine adjustment phase to reach the target weight.
This approach compensates for variations in bulk density and provides better control over the final weight.
It also allows gross and net weights to be recorded, facilitating production monitoring and quality improvement.
This type of operation is commonly used on dry product filling machines.
What is the difference between volumetric and gravimetric dosing for powders?
Accuracy
Volumetric dosing is highly accurate when density remains stable. However, any variation in density leads to variation in weight.
Gravimetric dosing directly tracks the actual weight and becomes more accurate above a few grams.
Throughput
Volumetric dosing operates at high speed and allows for high production rates.
Gravimetric dosing is slower, as it requires a stabilization phase to reach the target weight.
Product sensitivity
Volumetric dosing is sensitive to density variations caused by humidity, compaction, or particle size distribution.
Gravimetric dosing is more robust, as it adjusts the dosage based on the measured weight.
These effects are common in many applications, especially in fine powder filling.
Tooling and flexibility
Volumetric dosing requires tooling that is well adapted to the product to ensure a consistent flow.
Gravimetric dosing may, in some cases, require fewer tooling configurations, since variations in product distribution have less impact on the final result.
Production monitoring
Gravimetric dosing enables direct recording of gross and net weights, which is a major advantage for traceability and quality control.
In volumetric systems, achieving the same level of monitoring requires additional weighing systems.
Why is bulk density a key parameter?
Bulk density is the key parameter in volumetric dosing. Any variation in density leads to a variation in delivered weight.
This density can change depending on humidity, compaction, or particle size, as detailed in dry product applications.
This is why understanding the real behavior of the powder is essential before selecting a technology.
When should volumetric dosing be used?
Volumetric dosing is particularly suitable when:
- the product is homogeneous
- density is stable
- high throughput is required
- doses are below 1 kg
It is also a good choice when the process requires the product to be compacted or compressed during filling.
When should gravimetric dosing be used?
Gravimetric dosing becomes preferable when:
- product density varies
- weight accuracy is critical
- doses are larger
- production monitoring is required
It is also relevant when legal metrology is required.
Legal metrology: an advantage of gravimetric dosing
Gravimetric dosing can comply with legal metrology, after validation by an organization such as the French National Metrology Laboratory.
This provides a guarantee of quality in certain industries.
Volumetric vs gravimetric: quick comparison
| Criteria | Volumetric | Gravimetric |
|---|---|---|
| Principle | Screw rotation counting | Weight measurement |
| Reference | Volume | Mass |
| Accuracy | Depends on density | Direct weight control |
| Throughput | High | Lower |
| Product sensitivity | High | Lower |
| Production monitoring | Limited | Advanced |
| Legal metrology | No | Yes |
Why are trials essential?
Even with a good understanding of the product, the decision should not be theoretical.
Trials make it possible to validate:
- accuracy
- repeatability
- throughput
- actual powder behavior
- compatibility between product and technology
To secure your project, it is recommended to carry out trials with your product under real conditions.
Conclusion
The choice between volumetric and gravimetric dosing depends primarily on the product and its constraints.
Volumetric dosing is a fast and efficient solution when the powder is stable and throughput is a priority.
Gravimetric dosing becomes more relevant when weight accuracy, product variability, or traceability are key requirements.
In all cases, product characterization and trials remain essential to secure the right technology choice.
Louis Derangère
CEO of MOM Packaging — Industrial automation engineer and expert in precision dosing.